Merge remote-tracking branch 'origin/master' into source-path

configure.ac

@@ -184,7 +184,7 @@ fi
 
 # Look for OpenSSL, a required dependency. FIXME: this is only (maybe)
 # used by S3BinaryCacheStore.
-PKG_CHECK_MODULES([OPENSSL], [libcrypto], [CXXFLAGS="$OPENSSL_CFLAGS $CXXFLAGS"])
+PKG_CHECK_MODULES([OPENSSL], [libcrypto >= 1.1.1], [CXXFLAGS="$OPENSSL_CFLAGS $CXXFLAGS"])
 
 
 # Look for libarchive.

doc/manual/src/command-ref/opt-common.md

@@ -203,10 +203,9 @@ Most Nix commands accept the following command-line options:
     instead.
 
   - <span id="opt-I">[`-I`](#opt-I)</span> *path*\
-    Add a path to the Nix expression search path. This option may be
+    Add an entry to the [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path).
-    given multiple times. See the `NIX_PATH` environment variable for
+    This option may be given multiple times.
-    information on the semantics of the Nix search path. Paths added
+    Paths added through `-I` take precedence over [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH).
-    through `-I` take precedence over `NIX_PATH`.
 
   - <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*\
     Set the Nix configuration option *name* to *value*. This overrides

doc/manual/src/glossary.md

@@ -127,7 +127,7 @@
     builder can rely on external inputs such as the network or the
     system time) but the Nix model assumes it.
 
-  - Nix database{#gloss-nix-database}\
+  - [Nix database]{#gloss-nix-database}\
     An SQlite database to track [reference]s between [store object]s.
     This is an implementation detail of the [local store].
 

doc/manual/src/installation/installing-binary.md

@@ -136,7 +136,7 @@ which you may remove.
 
 ### macOS
 
-1. Edit `/etc/zshrc` and `/etc/bashrc` to remove the lines sourcing
+1. Edit `/etc/zshrc`, `/etc/bashrc`, and `/etc/bash.bashrc` to remove the lines sourcing
    `nix-daemon.sh`, which should look like this:
 
    ```bash
@@ -153,6 +153,7 @@ which you may remove.
    ```console
    sudo mv /etc/zshrc.backup-before-nix /etc/zshrc
    sudo mv /etc/bashrc.backup-before-nix /etc/bashrc
+   sudo mv /etc/bash.bashrc.backup-before-nix /etc/bash.bashrc
    ```
 
    This will stop shells from sourcing the file and bringing everything you

perl/lib/Nix/Store.xs

@@ -27,8 +27,6 @@ static ref<Store> store()
     if (!_store) {
         try {
             initLibStore();
-            loadConfFile();
-            settings.lockCPU = false;
             _store = openStore();
         } catch (Error & e) {
             croak("%s", e.what());
@@ -295,7 +293,13 @@ SV * makeFixedOutputPath(int recursive, char * algo, char * hash, char * name)
         try {
             auto h = Hash::parseAny(hash, parseHashType(algo));
             auto method = recursive ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat;
-            auto path = store()->makeFixedOutputPath(method, h, name);
+            auto path = store()->makeFixedOutputPath(name, FixedOutputInfo {
+                .hash = {
+                    .method = method,
+                    .hash = h,
+                },
+                .references = {},
+            });
             XPUSHs(sv_2mortal(newSVpv(store()->printStorePath(path).c_str(), 0)));
         } catch (Error & e) {
             croak("%s", e.what());

src/build-remote/build-remote.cc

@@ -311,8 +311,9 @@ connected:
                 auto thisOutputId = DrvOutput{ thisOutputHash, outputName };
                 if (!store->queryRealisation(thisOutputId)) {
                     debug("missing output %s", outputName);
-                    assert(result.builtOutputs.count(thisOutputId));
+                    auto i = result.builtOutputs.find(outputName);
-                    auto newRealisation = result.builtOutputs.at(thisOutputId);
+                    assert(i != result.builtOutputs.end());
+                    auto & newRealisation = i->second;
                     missingRealisations.insert(newRealisation);
                     missingPaths.insert(newRealisation.outPath);
                 }

src/libcmd/installable-flake.cc

@@ -106,10 +106,10 @@ DerivedPathsWithInfo InstallableFlake::toDerivedPaths()
         }
 
         else if (v.type() == nString) {
-            PathSet context;
+            NixStringContext context;
             auto s = state->forceString(v, context, noPos, fmt("while evaluating the flake output attribute '%s'", attrPath));
             auto storePath = state->store->maybeParseStorePath(s);
-            if (storePath && context.count(std::string(s))) {
+            if (storePath && context.count(NixStringContextElem::Opaque { .path = *storePath })) {
                 return {{
                     .path = DerivedPath::Opaque {
                         .path = std::move(*storePath),

src/libcmd/installables.cc

@@ -593,8 +593,8 @@ std::vector<std::pair<ref<Installable>, BuiltPathWithResult>> Installable::build
                 std::visit(overloaded {
                     [&](const DerivedPath::Built & bfd) {
                         std::map<std::string, StorePath> outputs;
-                        for (auto & path : buildResult.builtOutputs)
+                        for (auto & [outputName, realisation] : buildResult.builtOutputs)
-                            outputs.emplace(path.first.outputName, path.second.outPath);
+                            outputs.emplace(outputName, realisation.outPath);
                         res.push_back({aux.installable, {
                             .path = BuiltPath::Built { bfd.drvPath, outputs },
                             .info = aux.info,

src/libcmd/repl.cc

@@ -593,7 +593,7 @@ bool NixRepl::processLine(std::string line)
 
         const auto [path, line] = [&] () -> std::pair<SourcePath, uint32_t> {
             if (v.type() == nPath || v.type() == nString) {
-                PathSet context;
+                NixStringContext context;
                 auto path = state->coerceToPath(noPos, v, context, "while evaluating the filename to edit");
                 return {path, 0};
             } else if (v.isLambda()) {
@@ -936,7 +936,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
         if (isDrv) {
             str << "«derivation ";
             Bindings::iterator i = v.attrs->find(state->sDrvPath);
-            PathSet context;
+            NixStringContext context;
             if (i != v.attrs->end())
                 str << state->store->printStorePath(state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the drvPath of a derivation"));
             else

src/libexpr/attr-path.cc

@@ -118,7 +118,7 @@ std::pair<SourcePath, uint32_t> findPackageFilename(EvalState & state, Value & v
 
     // FIXME: is it possible to extract the Pos object instead of doing this
     //        toString + parsing?
-    PathSet context;
+    NixStringContext context;
     auto path = state.coerceToPath(noPos, *v2, context, "while evaluating the 'meta.position' attribute of a derivation");
 
     auto fn = path.path.abs();

src/libexpr/eval-cache.cc

@@ -47,7 +47,7 @@ struct AttrDb
     {
         auto state(_state->lock());
 
-        Path cacheDir = getCacheDir() + "/nix/eval-cache-v4";
+        Path cacheDir = getCacheDir() + "/nix/eval-cache-v5";
         createDirs(cacheDir);
 
         Path dbPath = cacheDir + "/" + fingerprint.to_string(Base16, false) + ".sqlite";
@@ -300,7 +300,7 @@ struct AttrDb
                 NixStringContext context;
                 if (!queryAttribute.isNull(3))
                     for (auto & s : tokenizeString<std::vector<std::string>>(queryAttribute.getStr(3), ";"))
-                        context.push_back(NixStringContextElem::parse(cfg, s));
+                        context.insert(NixStringContextElem::parse(s));
                 return {{rowId, string_t{queryAttribute.getStr(2), context}}};
             }
             case AttrType::Bool:
@@ -621,9 +621,11 @@ string_t AttrCursor::getStringWithContext()
 
     auto & v = forceValue();
 
-    if (v.type() == nString)
+    if (v.type() == nString) {
-        return {v.string.s, v.getContext(*root->state.store)};
+        NixStringContext context;
-    else if (v.type() == nPath)
+        copyContext(v, context);
+        return {v.string.s, std::move(context)};
+    } else if (v.type() == nPath)
         return {v.path().to_string(), {}};
     else
         root->state.error("'%s' is not a string but %s", getAttrPathStr()).debugThrow<TypeError>();

src/libexpr/eval.cc

@@ -610,8 +610,7 @@ void EvalState::allowAndSetStorePathString(const StorePath & storePath, Value &
 {
     allowPath(storePath);
 
-    auto path = store->printStorePath(storePath);
+    mkStorePathString(storePath, v);
-    v.mkString(path, PathSet({path}));
 }
 
 SourcePath EvalState::checkSourcePath(const SourcePath & path_)
@@ -693,7 +692,7 @@ void EvalState::checkURI(const std::string & uri)
 }
 
 
-Path EvalState::toRealPath(const Path & path, const PathSet & context)
+Path EvalState::toRealPath(const Path & path, const NixStringContext & context)
 {
     // FIXME: check whether 'path' is in 'context'.
     return
@@ -945,25 +944,25 @@ void Value::mkString(std::string_view s)
 }
 
 
-static void copyContextToValue(Value & v, const PathSet & context)
+static void copyContextToValue(Value & v, const NixStringContext & context)
 {
     if (!context.empty()) {
         size_t n = 0;
         v.string.context = (const char * *)
             allocBytes((context.size() + 1) * sizeof(char *));
         for (auto & i : context)
-            v.string.context[n++] = dupString(i.c_str());
+            v.string.context[n++] = dupString(i.to_string().c_str());
         v.string.context[n] = 0;
     }
 }
 
-void Value::mkString(std::string_view s, const PathSet & context)
+void Value::mkString(std::string_view s, const NixStringContext & context)
 {
     mkString(s);
     copyContextToValue(*this, context);
 }
 
-void Value::mkStringMove(const char * s, const PathSet & context)
+void Value::mkStringMove(const char * s, const NixStringContext & context)
 {
     mkString(s);
     copyContextToValue(*this, context);
@@ -1039,6 +1038,16 @@ void EvalState::mkPos(Value & v, PosIdx p)
 }
 
 
+void EvalState::mkStorePathString(const StorePath & p, Value & v)
+{
+    v.mkString(
+        store->printStorePath(p),
+        NixStringContext {
+            NixStringContextElem::Opaque { .path = p },
+        });
+}
+
+
 /* Create a thunk for the delayed computation of the given expression
    in the given environment.  But if the expression is a variable,
    then look it up right away.  This significantly reduces the number
@@ -1901,7 +1910,7 @@ void EvalState::concatLists(Value & v, size_t nrLists, Value * * lists, const Po
 
 void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     std::vector<BackedStringView> s;
     size_t sSize = 0;
     NixInt n = 0;
@@ -2110,26 +2119,15 @@ std::string_view EvalState::forceString(Value & v, const PosIdx pos, std::string
 }
 
 
-void copyContext(const Value & v, PathSet & context)
+void copyContext(const Value & v, NixStringContext & context)
 {
     if (v.string.context)
         for (const char * * p = v.string.context; *p; ++p)
-            context.insert(*p);
+            context.insert(NixStringContextElem::parse(*p));
 }
 
 
-NixStringContext Value::getContext(const Store & store)
+std::string_view EvalState::forceString(Value & v, NixStringContext & context, const PosIdx pos, std::string_view errorCtx)
-{
-    NixStringContext res;
-    assert(internalType == tString);
-    if (string.context)
-        for (const char * * p = string.context; *p; ++p)
-            res.push_back(NixStringContextElem::parse(store, *p));
-    return res;
-}
-
-
-std::string_view EvalState::forceString(Value & v, PathSet & context, const PosIdx pos, std::string_view errorCtx)
 {
     auto s = forceString(v, pos, errorCtx);
     copyContext(v, context);
@@ -2159,7 +2157,7 @@ bool EvalState::isDerivation(Value & v)
 
 
 std::optional<std::string> EvalState::tryAttrsToString(const PosIdx pos, Value & v,
-    PathSet & context, bool coerceMore, bool copyToStore)
+    NixStringContext & context, bool coerceMore, bool copyToStore)
 {
     auto i = v.attrs->find(sToString);
     if (i != v.attrs->end()) {
@@ -2176,7 +2174,7 @@ std::optional<std::string> EvalState::tryAttrsToString(const PosIdx pos, Value &
 BackedStringView EvalState::coerceToString(
     const PosIdx pos,
     Value & v,
-    PathSet & context,
+    NixStringContext & context,
     std::string_view errorCtx,
     bool coerceMore,
     bool copyToStore,
@@ -2258,7 +2256,7 @@ BackedStringView EvalState::coerceToString(
 }
 
 
-StorePath EvalState::copyPathToStore(PathSet & context, const SourcePath & path)
+StorePath EvalState::copyPathToStore(NixStringContext & context, const SourcePath & path)
 {
     if (nix::isDerivation(path.path.abs()))
         error("file names are not allowed to end in '%1%'", drvExtension).debugThrow<EvalError>();
@@ -2275,12 +2273,14 @@ StorePath EvalState::copyPathToStore(PathSet & context, const SourcePath & path)
             return dstPath;
         }();
 
-    context.insert(store->printStorePath(dstPath));
+    context.insert(NixStringContextElem::Opaque {
+        .path = dstPath
+    });
     return dstPath;
 }
 
 
-SourcePath EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
+SourcePath EvalState::coerceToPath(const PosIdx pos, Value & v, NixStringContext & context, std::string_view errorCtx)
 {
     auto path = coerceToString(pos, v, context, errorCtx, false, false, true).toOwned();
     if (path == "" || path[0] != '/')
@@ -2289,7 +2289,7 @@ SourcePath EvalState::coerceToPath(const PosIdx pos, Value & v, PathSet & contex
 }
 
 
-StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx)
+StorePath EvalState::coerceToStorePath(const PosIdx pos, Value & v, NixStringContext & context, std::string_view errorCtx)
 {
     auto path = coerceToString(pos, v, context, errorCtx, false, false, true).toOwned();
     if (auto storePath = store->maybeParseStorePath(path))
@@ -2496,7 +2496,7 @@ void EvalState::printStats()
 }
 
 
-std::string ExternalValueBase::coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const
+std::string ExternalValueBase::coerceToString(const Pos & pos, NixStringContext & context, bool copyMore, bool copyToStore) const
 {
     throw TypeError({
         .msg = hintfmt("cannot coerce %1% to a string", showType())

src/libexpr/eval.hh

@@ -57,7 +57,7 @@ void printEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env &
 
 std::unique_ptr<ValMap> mapStaticEnvBindings(const SymbolTable & st, const StaticEnv & se, const Env & env);
 
-void copyContext(const Value & v, PathSet & context);
+void copyContext(const Value & v, NixStringContext & context);
 
 
 std::string printValue(const EvalState & state, const Value & v);
@@ -330,7 +330,7 @@ public:
      * intended to distinguish between import-from-derivation and
      * sources stored in the actual /nix/store.
      */
-    Path toRealPath(const Path & path, const PathSet & context);
+    Path toRealPath(const Path & path, const NixStringContext & context);
 
     /**
      * Parse a Nix expression from the specified file.
@@ -426,7 +426,7 @@ public:
      */
     void forceFunction(Value & v, const PosIdx pos, std::string_view errorCtx);
     std::string_view forceString(Value & v, const PosIdx pos, std::string_view errorCtx);
-    std::string_view forceString(Value & v, PathSet & context, const PosIdx pos, std::string_view errorCtx);
+    std::string_view forceString(Value & v, NixStringContext & context, const PosIdx pos, std::string_view errorCtx);
     std::string_view forceStringNoCtx(Value & v, const PosIdx pos, std::string_view errorCtx);
 
     [[gnu::noinline]]
@@ -442,7 +442,7 @@ public:
     bool isDerivation(Value & v);
 
     std::optional<std::string> tryAttrsToString(const PosIdx pos, Value & v,
-        PathSet & context, bool coerceMore = false, bool copyToStore = true);
+        NixStringContext & context, bool coerceMore = false, bool copyToStore = true);
 
     /**
      * String coercion.
@@ -452,12 +452,12 @@ public:
      * booleans and lists to a string.  If `copyToStore` is set,
      * referenced paths are copied to the Nix store as a side effect.
      */
-    BackedStringView coerceToString(const PosIdx pos, Value & v, PathSet & context,
+    BackedStringView coerceToString(const PosIdx pos, Value & v, NixStringContext & context,
         std::string_view errorCtx,
         bool coerceMore = false, bool copyToStore = true,
         bool canonicalizePath = true);
 
-    StorePath copyPathToStore(PathSet & context, const SourcePath & path);
+    StorePath copyPathToStore(NixStringContext & context, const SourcePath & path);
 
     /**
      * Path coercion.
@@ -466,12 +466,12 @@ public:
      * path.  The result is guaranteed to be a canonicalised, absolute
      * path.  Nothing is copied to the store.
      */
-    SourcePath coerceToPath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx);
+    SourcePath coerceToPath(const PosIdx pos, Value & v, NixStringContext & context, std::string_view errorCtx);
 
     /**
      * Like coerceToPath, but the result must be a store path.
      */
-    StorePath coerceToStorePath(const PosIdx pos, Value & v, PathSet & context, std::string_view errorCtx);
+    StorePath coerceToStorePath(const PosIdx pos, Value & v, NixStringContext & context, std::string_view errorCtx);
 
 public:
 
@@ -576,6 +576,12 @@ public:
     void mkThunk_(Value & v, Expr * expr);
     void mkPos(Value & v, PosIdx pos);
 
+    /* Create a string representing a store path.
+
+       The string is the printed store path with a context containing a single
+       `Opaque` element of that store path. */
+    void mkStorePathString(const StorePath & storePath, Value & v);
+
     void concatLists(Value & v, size_t nrLists, Value * * lists, const PosIdx pos, std::string_view errorCtx);
 
     /**
@@ -587,7 +593,7 @@ public:
      * Realise the given context, and return a mapping from the placeholders
      * used to construct the associated value to their final store path
      */
-    [[nodiscard]] StringMap realiseContext(const PathSet & context);
+    [[nodiscard]] StringMap realiseContext(const NixStringContext & context);
 
 private:
 

src/libexpr/flake/config.cc

@@ -31,7 +31,7 @@ static void writeTrustedList(const TrustedList & trustedList)
 
 void ConfigFile::apply()
 {
-    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-prefix", "bash-prompt-suffix", "flake-registry"};
+    std::set<std::string> whitelist{"bash-prompt", "bash-prompt-prefix", "bash-prompt-suffix", "flake-registry", "commit-lockfile-summary"};
 
     for (auto & [name, value] : settings) {
 

src/libexpr/flake/flake.cc

@@ -265,7 +265,7 @@ static Flake getFlake(
                     state.symbols[setting.name],
                     std::string(state.forceStringNoCtx(*setting.value, setting.pos, "")));
             else if (setting.value->type() == nPath) {
-                PathSet emptyContext = {};
+                NixStringContext emptyContext = {};
                 flake.config.settings.emplace(
                     state.symbols[setting.name],
                     state.coerceToString(setting.pos, *setting.value, emptyContext, "", false, true, true) .toOwned());

src/libexpr/get-drvs.cc

@@ -71,7 +71,7 @@ std::optional<StorePath> DrvInfo::queryDrvPath() const
 {
     if (!drvPath && attrs) {
         Bindings::iterator i = attrs->find(state->sDrvPath);
-        PathSet context;
+        NixStringContext context;
         if (i == attrs->end())
             drvPath = {std::nullopt};
         else
@@ -93,7 +93,7 @@ StorePath DrvInfo::queryOutPath() const
 {
     if (!outPath && attrs) {
         Bindings::iterator i = attrs->find(state->sOutPath);
-        PathSet context;
+        NixStringContext context;
         if (i != attrs->end())
             outPath = state->coerceToStorePath(i->pos, *i->value, context, "while evaluating the output path of a derivation");
     }
@@ -124,7 +124,7 @@ DrvInfo::Outputs DrvInfo::queryOutputs(bool withPaths, bool onlyOutputsToInstall
                     /* And evaluate its ‘outPath’ attribute. */
                     Bindings::iterator outPath = out->value->attrs->find(state->sOutPath);
                     if (outPath == out->value->attrs->end()) continue; // FIXME: throw error?
-                    PathSet context;
+                    NixStringContext context;
                     outputs.emplace(output, state->coerceToStorePath(outPath->pos, *outPath->value, context, "while evaluating an output path of a derivation"));
                 } else
                     outputs.emplace(output, std::nullopt);

src/libexpr/primops.cc

@@ -38,17 +38,16 @@ namespace nix {
 InvalidPathError::InvalidPathError(const Path & path) :
     EvalError("path '%s' is not valid", path), path(path) {}
 
-StringMap EvalState::realiseContext(const PathSet & context)
+StringMap EvalState::realiseContext(const NixStringContext & context)
 {
     std::vector<DerivedPath::Built> drvs;
     StringMap res;
 
-    for (auto & c_ : context) {
+    for (auto & c : context) {
         auto ensureValid = [&](const StorePath & p) {
             if (!store->isValidPath(p))
                 debugThrowLastTrace(InvalidPathError(store->printStorePath(p)));
         };
-        auto c = NixStringContextElem::parse(*store, c_);
         std::visit(overloaded {
             [&](const NixStringContextElem::Built & b) {
                 drvs.push_back(DerivedPath::Built {
@@ -112,7 +111,7 @@ struct RealisePathFlags {
 
 static SourcePath realisePath(EvalState & state, const PosIdx pos, Value & v, const RealisePathFlags flags = {})
 {
-    PathSet context;
+    NixStringContext context;
 
     auto path = state.coerceToPath(noPos, v, context, "while realising the context of a path");
 
@@ -158,7 +157,12 @@ static void mkOutputString(
             /* FIXME: we need to depend on the basic derivation, not
                derivation */
             : downstreamPlaceholder(*state.store, drvPath, o.first),
-        {"!" + o.first + "!" + state.store->printStorePath(drvPath)});
+        NixStringContext {
+            NixStringContextElem::Built {
+                .drvPath = drvPath,
+                .output = o.first,
+            }
+        });
 }
 
 /* Load and evaluate an expression from path specified by the
@@ -178,17 +182,18 @@ static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * v
         return storePath;
     };
 
-    if (auto optStorePath = isValidDerivationInStore()) {
+    if (auto storePath = isValidDerivationInStore()) {
-        auto storePath = *optStorePath;
+        Derivation drv = state.store->readDerivation(*storePath);
-        Derivation drv = state.store->readDerivation(storePath);
         auto attrs = state.buildBindings(3 + drv.outputs.size());
-        attrs.alloc(state.sDrvPath).mkString(path2, {"=" + path2});
+        attrs.alloc(state.sDrvPath).mkString(path2, {
+            NixStringContextElem::DrvDeep { .drvPath = *storePath },
+        });
         attrs.alloc(state.sName).mkString(drv.env["name"]);
         auto & outputsVal = attrs.alloc(state.sOutputs);
         state.mkList(outputsVal, drv.outputs.size());
 
         for (const auto & [i, o] : enumerate(drv.outputs)) {
-            mkOutputString(state, attrs, storePath, drv, o);
+            mkOutputString(state, attrs, *storePath, drv, o);
             (outputsVal.listElems()[i] = state.allocValue())->mkString(o.first);
         }
 
@@ -359,7 +364,7 @@ void prim_exec(EvalState & state, const PosIdx pos, Value * * args, Value & v)
     auto count = args[0]->listSize();
     if (count == 0)
         state.error("at least one argument to 'exec' required").atPos(pos).debugThrow<EvalError>();
-    PathSet context;
+    NixStringContext context;
     auto program = state.coerceToString(pos, *elems[0], context,
             "while evaluating the first element of the argument passed to builtins.exec",
             false, false).toOwned();
@@ -769,7 +774,7 @@ static RegisterPrimOp primop_abort({
     )",
     .fun = [](EvalState & state, const PosIdx pos, Value * * args, Value & v)
     {
-        PathSet context;
+        NixStringContext context;
         auto s = state.coerceToString(pos, *args[0], context,
                 "while evaluating the error message passed to builtins.abort").toOwned();
         state.debugThrowLastTrace(Abort("evaluation aborted with the following error message: '%1%'", s));
@@ -788,7 +793,7 @@ static RegisterPrimOp primop_throw({
     )",
     .fun = [](EvalState & state, const PosIdx pos, Value * * args, Value & v)
     {
-      PathSet context;
+      NixStringContext context;
       auto s = state.coerceToString(pos, *args[0], context,
               "while evaluating the error message passed to builtin.throw").toOwned();
       state.debugThrowLastTrace(ThrownError(s));
@@ -801,7 +806,7 @@ static void prim_addErrorContext(EvalState & state, const PosIdx pos, Value * *
         state.forceValue(*args[1], pos);
         v = *args[1];
     } catch (Error & e) {
-        PathSet context;
+        NixStringContext context;
         auto message = state.coerceToString(pos, *args[0], context,
                 "while evaluating the error message passed to builtins.addErrorContext",
                 false, false).toOwned();
@@ -1087,7 +1092,7 @@ drvName, Bindings * attrs, Value & v)
     Derivation drv;
     drv.name = drvName;
 
-    PathSet context;
+    NixStringContext context;
 
     bool contentAddressed = false;
     bool isImpure = false;
@@ -1233,8 +1238,7 @@ drvName, Bindings * attrs, Value & v)
     /* Everything in the context of the strings in the derivation
        attributes should be added as dependencies of the resulting
        derivation. */
-    for (auto & c_ : context) {
+    for (auto & c : context) {
-        auto c = NixStringContextElem::parse(*state.store, c_);
         std::visit(overloaded {
             /* Since this allows the builder to gain access to every
                path in the dependency graph of the derivation (including
@@ -1294,7 +1298,13 @@ drvName, Bindings * attrs, Value & v)
         auto h = newHashAllowEmpty(*outputHash, parseHashTypeOpt(outputHashAlgo));
 
         auto method = ingestionMethod.value_or(FileIngestionMethod::Flat);
-        auto outPath = state.store->makeFixedOutputPath(method, h, drvName);
+        auto outPath = state.store->makeFixedOutputPath(drvName, FixedOutputInfo {
+            .hash = {
+                .method = method,
+                .hash = h,
+            },
+            .references = {},
+        });
         drv.env["out"] = state.store->printStorePath(outPath);
         drv.outputs.insert_or_assign("out",
             DerivationOutput::CAFixed {
@@ -1387,7 +1397,9 @@ drvName, Bindings * attrs, Value & v)
     }
 
     auto result = state.buildBindings(1 + drv.outputs.size());
-    result.alloc(state.sDrvPath).mkString(drvPathS, {"=" + drvPathS});
+    result.alloc(state.sDrvPath).mkString(drvPathS, {
+        NixStringContextElem::DrvDeep { .drvPath = drvPath },
+    });
     for (auto & i : drv.outputs)
         mkOutputString(state, result, drvPath, drv, i);
 
@@ -1432,7 +1444,7 @@ static RegisterPrimOp primop_placeholder({
 /* Convert the argument to a path.  !!! obsolete? */
 static void prim_toPath(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto path = state.coerceToPath(pos, *args[0], context, "while evaluating the first argument passed to builtins.toPath");
     v.mkString(path.path.abs(), context);
 }
@@ -1463,7 +1475,7 @@ static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args,
             .errPos = state.positions[pos]
         }));
 
-    PathSet context;
+    NixStringContext context;
     auto path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context, "while evaluating the first argument passed to builtins.storePath")).path;
     /* Resolve symlinks in ‘path’, unless ‘path’ itself is a symlink
        directly in the store.  The latter condition is necessary so
@@ -1478,7 +1490,7 @@ static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args,
     auto path2 = state.store->toStorePath(path.abs()).first;
     if (!settings.readOnlyMode)
         state.store->ensurePath(path2);
-    context.insert(state.store->printStorePath(path2));
+    context.insert(NixStringContextElem::Opaque { .path = path2 });
     v.mkString(path.abs(), context);
 }
 
@@ -1534,7 +1546,7 @@ static RegisterPrimOp primop_pathExists({
    following the last slash. */
 static void prim_baseNameOf(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     v.mkString(baseNameOf(*state.coerceToString(pos, *args[0], context,
             "while evaluating the first argument passed to builtins.baseNameOf",
             false, false)), context);
@@ -1556,12 +1568,12 @@ static RegisterPrimOp primop_baseNameOf({
    of the argument. */
 static void prim_dirOf(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
     state.forceValue(*args[0], pos);
     if (args[0]->type() == nPath) {
         auto path = args[0]->path();
         v.mkPath(path.path.isRoot() ? path : path.parent());
     } else {
+        NixStringContext context;
         auto path = state.coerceToString(pos, *args[0], context,
             "while evaluating the first argument passed to 'builtins.dirOf'",
             false, false);
@@ -1599,7 +1611,12 @@ static void prim_readFile(EvalState & state, const PosIdx pos, Value * * args, V
         refsSink << s;
         refs = refsSink.getResultPaths();
     }
-    auto context = state.store->printStorePathSet(refs);
+    NixStringContext context;
+    for (auto && p : std::move(refs)) {
+        context.insert(NixStringContextElem::Opaque {
+            .path = std::move((StorePath &&)p),
+        });
+    }
     v.mkString(s, context);
 }
 
@@ -1630,7 +1647,7 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value * * args, V
 
         i = getAttr(state, state.sPath, v2->attrs, "in an element of the __nixPath");
 
-        PathSet context;
+        NixStringContext context;
         auto path = state.coerceToString(pos, *i->value, context,
                 "while evaluating the `path` attribute of an element of the list passed to builtins.findFile",
                 false, false).toOwned();
@@ -1781,7 +1798,7 @@ static RegisterPrimOp primop_readDir({
 static void prim_toXML(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     std::ostringstream out;
-    PathSet context;
+    NixStringContext context;
     printValueAsXML(state, true, false, *args[0], out, context, pos);
     v.mkString(out.str(), context);
 }
@@ -1889,7 +1906,7 @@ static RegisterPrimOp primop_toXML({
 static void prim_toJSON(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     std::ostringstream out;
-    PathSet context;
+    NixStringContext context;
     printValueAsJSON(state, true, *args[0], pos, out, context);
     v.mkString(out.str(), context);
 }
@@ -1939,22 +1956,23 @@ static RegisterPrimOp primop_fromJSON({
    as an input by derivations. */
 static void prim_toFile(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     std::string name(state.forceStringNoCtx(*args[0], pos, "while evaluating the first argument passed to builtins.toFile"));
     std::string contents(state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.toFile"));
 
     StorePathSet refs;
 
-    for (auto path : context) {
+    for (auto c : context) {
-        if (path.at(0) != '/')
+        if (auto p = std::get_if<NixStringContextElem::Opaque>(&c))
+            refs.insert(p->path);
+        else
             state.debugThrowLastTrace(EvalError({
                 .msg = hintfmt(
                     "in 'toFile': the file named '%1%' must not contain a reference "
                     "to a derivation but contains (%2%)",
-                    name, path),
+                    name, c.to_string()),
                 .errPos = state.positions[pos]
             }));
-        refs.insert(state.store->parseStorePath(path));
     }
 
     auto storePath = settings.readOnlyMode
@@ -2055,7 +2073,7 @@ static void addPath(
     FileIngestionMethod method,
     const std::optional<Hash> expectedHash,
     Value & v,
-    const PathSet & context)
+    const NixStringContext & context)
 {
     try {
         // FIXME: handle CA derivation outputs (where path needs to
@@ -2103,7 +2121,13 @@ static void addPath(
 
         std::optional<StorePath> expectedStorePath;
         if (expectedHash)
-            expectedStorePath = state.store->makeFixedOutputPath(method, *expectedHash, name);
+            expectedStorePath = state.store->makeFixedOutputPath(name, FixedOutputInfo {
+                .hash = {
+                    .method = method,
+                    .hash = *expectedHash,
+                },
+                .references = {},
+            });
 
         if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
             StorePath dstPath = settings.readOnlyMode
@@ -2123,7 +2147,7 @@ static void addPath(
 
 static void prim_filterSource(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto path = state.coerceToPath(pos, *args[1], context,
         "while evaluating the second argument (the path to filter) passed to builtins.filterSource");
     state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.filterSource");
@@ -2192,7 +2216,7 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
     Value * filterFun = nullptr;
     auto method = FileIngestionMethod::Recursive;
     std::optional<Hash> expectedHash;
-    PathSet context;
+    NixStringContext context;
 
     state.forceAttrs(*args[0], pos, "while evaluating the argument passed to 'builtins.path'");
 
@@ -3528,7 +3552,7 @@ static RegisterPrimOp primop_lessThan({
    `"/nix/store/whatever..."'. */
 static void prim_toString(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto s = state.coerceToString(pos, *args[0], context,
             "while evaluating the first argument passed to builtins.toString",
             true, false);
@@ -3567,7 +3591,7 @@ static void prim_substring(EvalState & state, const PosIdx pos, Value * * args,
 {
     int start = state.forceInt(*args[0], pos, "while evaluating the first argument (the start offset) passed to builtins.substring");
     int len = state.forceInt(*args[1], pos, "while evaluating the second argument (the substring length) passed to builtins.substring");
-    PathSet context;
+    NixStringContext context;
     auto s = state.coerceToString(pos, *args[2], context, "while evaluating the third argument (the string) passed to builtins.substring");
 
     if (start < 0)
@@ -3601,7 +3625,7 @@ static RegisterPrimOp primop_substring({
 
 static void prim_stringLength(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.stringLength");
     v.mkInt(s->size());
 }
@@ -3627,7 +3651,7 @@ static void prim_hashString(EvalState & state, const PosIdx pos, Value * * args,
             .errPos = state.positions[pos]
         }));
 
-    PathSet context; // discarded
+    NixStringContext context; // discarded
     auto s = state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.hashString");
 
     v.mkString(hashString(*ht, s).to_string(Base16, false));
@@ -3673,7 +3697,7 @@ void prim_match(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 
         auto regex = state.regexCache->get(re);
 
-        PathSet context;
+        NixStringContext context;
         const auto str = state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.match");
 
         std::cmatch match;
@@ -3753,7 +3777,7 @@ void prim_split(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 
         auto regex = state.regexCache->get(re);
 
-        PathSet context;
+        NixStringContext context;
         const auto str = state.forceString(*args[1], context, pos, "while evaluating the second argument passed to builtins.split");
 
         auto begin = std::cregex_iterator(str.begin(), str.end(), regex);
@@ -3850,7 +3874,7 @@ static RegisterPrimOp primop_split({
 
 static void prim_concatStringsSep(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
 
     auto sep = state.forceString(*args[0], context, pos, "while evaluating the first argument (the separator string) passed to builtins.concatStringsSep");
     state.forceList(*args[1], pos, "while evaluating the second argument (the list of strings to concat) passed to builtins.concatStringsSep");
@@ -3890,15 +3914,15 @@ static void prim_replaceStrings(EvalState & state, const PosIdx pos, Value * * a
     for (auto elem : args[0]->listItems())
         from.emplace_back(state.forceString(*elem, pos, "while evaluating one of the strings to replace passed to builtins.replaceStrings"));
 
-    std::vector<std::pair<std::string, PathSet>> to;
+    std::vector<std::pair<std::string, NixStringContext>> to;
     to.reserve(args[1]->listSize());
     for (auto elem : args[1]->listItems()) {
-        PathSet ctx;
+        NixStringContext ctx;
         auto s = state.forceString(*elem, ctx, pos, "while evaluating one of the replacement strings passed to builtins.replaceStrings");
         to.emplace_back(s, std::move(ctx));
     }
 
-    PathSet context;
+    NixStringContext context;
     auto s = state.forceString(*args[2], context, pos, "while evaluating the third argument passed to builtins.replaceStrings");
 
     std::string res;

src/libexpr/primops/context.cc

@@ -7,7 +7,7 @@ namespace nix {
 
 static void prim_unsafeDiscardStringContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardStringContext");
     v.mkString(*s);
 }
@@ -17,7 +17,7 @@ static RegisterPrimOp primop_unsafeDiscardStringContext("__unsafeDiscardStringCo
 
 static void prim_hasContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.hasContext");
     v.mkBool(!context.empty());
 }
@@ -33,17 +33,18 @@ static RegisterPrimOp primop_hasContext("__hasContext", 1, prim_hasContext);
    drv.inputDrvs. */
 static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.unsafeDiscardOutputDependency");
 
-    PathSet context2;
+    NixStringContext context2;
-    for (auto && p : context) {
+    for (auto && c : context) {
-        auto c = NixStringContextElem::parse(*state.store, p);
         if (auto * ptr = std::get_if<NixStringContextElem::DrvDeep>(&c)) {
-            context2.emplace(state.store->printStorePath(ptr->drvPath));
+            context2.emplace(NixStringContextElem::Opaque {
+                .path = ptr->drvPath
+            });
         } else {
             /* Can reuse original item */
-            context2.emplace(std::move(p));
+            context2.emplace(std::move(c));
         }
     }
 
@@ -79,22 +80,21 @@ static void prim_getContext(EvalState & state, const PosIdx pos, Value * * args,
         bool allOutputs = false;
         Strings outputs;
     };
-    PathSet context;
+    NixStringContext context;
     state.forceString(*args[0], context, pos, "while evaluating the argument passed to builtins.getContext");
     auto contextInfos = std::map<StorePath, ContextInfo>();
-    for (const auto & p : context) {
+    for (auto && i : context) {
-        NixStringContextElem ctx = NixStringContextElem::parse(*state.store, p);
         std::visit(overloaded {
-            [&](NixStringContextElem::DrvDeep & d) {
+            [&](NixStringContextElem::DrvDeep && d) {
-                contextInfos[d.drvPath].allOutputs = true;
+                contextInfos[std::move(d.drvPath)].allOutputs = true;
             },
-            [&](NixStringContextElem::Built & b) {
+            [&](NixStringContextElem::Built && b) {
-                contextInfos[b.drvPath].outputs.emplace_back(std::move(b.output));
+                contextInfos[std::move(b.drvPath)].outputs.emplace_back(std::move(b.output));
             },
-            [&](NixStringContextElem::Opaque & o) {
+            [&](NixStringContextElem::Opaque && o) {
-                contextInfos[o.path].path = true;
+                contextInfos[std::move(o.path)].path = true;
             },
-        }, ctx.raw());
+        }, ((NixStringContextElem &&) i).raw());
     }
 
     auto attrs = state.buildBindings(contextInfos.size());
@@ -129,7 +129,7 @@ static RegisterPrimOp primop_getContext("__getContext", 1, prim_getContext);
 */
 static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-    PathSet context;
+    NixStringContext context;
     auto orig = state.forceString(*args[0], context, noPos, "while evaluating the first argument passed to builtins.appendContext");
 
     state.forceAttrs(*args[1], pos, "while evaluating the second argument passed to builtins.appendContext");
@@ -143,13 +143,16 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
                 .msg = hintfmt("context key '%s' is not a store path", name),
                 .errPos = state.positions[i.pos]
             });
+        auto namePath = state.store->parseStorePath(name);
         if (!settings.readOnlyMode)
-            state.store->ensurePath(state.store->parseStorePath(name));
+            state.store->ensurePath(namePath);
         state.forceAttrs(*i.value, i.pos, "while evaluating the value of a string context");
         auto iter = i.value->attrs->find(sPath);
         if (iter != i.value->attrs->end()) {
             if (state.forceBool(*iter->value, iter->pos, "while evaluating the `path` attribute of a string context"))
-                context.emplace(name);
+                context.emplace(NixStringContextElem::Opaque {
+                    .path = namePath,
+                });
         }
 
         iter = i.value->attrs->find(sAllOutputs);
@@ -161,7 +164,9 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
                         .errPos = state.positions[i.pos]
                     });
                 }
-                context.insert(concatStrings("=", name));
+                context.emplace(NixStringContextElem::DrvDeep {
+                    .drvPath = namePath,
+                });
             }
         }
 
@@ -176,7 +181,10 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
             }
             for (auto elem : iter->value->listItems()) {
                 auto outputName = state.forceStringNoCtx(*elem, iter->pos, "while evaluating an output name within a string context");
-                context.insert(concatStrings("!", outputName, "!", name));
+                context.emplace(NixStringContextElem::Built {
+                    .drvPath = namePath,
+                    .output = std::string { outputName },
+                });
             }
         }
     }

src/libexpr/primops/fetchClosure.cc

@@ -18,7 +18,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
         const auto & attrName = state.symbols[attr.name];
 
         if (attrName == "fromPath") {
-            PathSet context;
+            NixStringContext context;
             fromPath = state.coerceToStorePath(attr.pos, *attr.value, context,
                     "while evaluating the 'fromPath' attribute passed to builtins.fetchClosure");
         }
@@ -27,7 +27,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
             state.forceValue(*attr.value, attr.pos);
             toCA = true;
             if (attr.value->type() != nString || attr.value->string.s != std::string("")) {
-                PathSet context;
+                NixStringContext context;
                 toPath = state.coerceToStorePath(attr.pos, *attr.value, context,
                         "while evaluating the 'toPath' attribute passed to builtins.fetchClosure");
             }
@@ -114,8 +114,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
             });
     }
 
-    auto toPathS = state.store->printStorePath(*toPath);
+    state.mkStorePathString(*toPath, v);
-    v.mkString(toPathS, {toPathS});
 }
 
 static RegisterPrimOp primop_fetchClosure({

src/libexpr/primops/fetchMercurial.cc

@@ -13,7 +13,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
     std::optional<Hash> rev;
     std::optional<std::string> ref;
     std::string_view name = "source";
-    PathSet context;
+    NixStringContext context;
 
     state.forceValue(*args[0], pos);
 
@@ -73,8 +73,7 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
     auto [tree, input2] = input.fetch(state.store);
 
     auto attrs2 = state.buildBindings(8);
-    auto storePath = state.store->printStorePath(tree.storePath);
+    state.mkStorePathString(tree.storePath, attrs2.alloc(state.sOutPath));
-    attrs2.alloc(state.sOutPath).mkString(storePath, {storePath});
     if (input2.getRef())
         attrs2.alloc("branch").mkString(*input2.getRef());
     // Backward compatibility: set 'rev' to

src/libexpr/primops/fetchTree.cc

@@ -24,9 +24,8 @@ void emitTreeAttrs(
 
     auto attrs = state.buildBindings(8);
 
-    auto storePath = state.store->printStorePath(tree.storePath);
 
-    attrs.alloc(state.sOutPath).mkString(storePath, {storePath});
+    state.mkStorePathString(tree.storePath, attrs.alloc(state.sOutPath));
 
     // FIXME: support arbitrary input attributes.
 
@@ -107,7 +106,7 @@ static void fetchTree(
     const FetchTreeParams & params = FetchTreeParams{}
 ) {
     fetchers::Input input;
-    PathSet context;
+    NixStringContext context;
 
     state.forceValue(*args[0], pos);
 
@@ -243,10 +242,15 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
 
     // early exit if pinned and already in the store
     if (expectedHash && expectedHash->type == htSHA256) {
-        auto expectedPath =
+        auto expectedPath = state.store->makeFixedOutputPath(
-            unpack
+            name,
-            ? state.store->makeFixedOutputPath(FileIngestionMethod::Recursive, *expectedHash, name, {})
+            FixedOutputInfo {
-            : state.store->makeFixedOutputPath(FileIngestionMethod::Flat, *expectedHash, name, {});
+                .hash = {
+                    .method = unpack ? FileIngestionMethod::Recursive : FileIngestionMethod::Flat,
+                    .hash = *expectedHash,
+                },
+                .references = {}
+            });
 
         if (state.store->isValidPath(expectedPath)) {
             state.allowAndSetStorePathString(expectedPath, v);

src/libexpr/tests/json.cc

@@ -8,7 +8,7 @@ namespace nix {
         protected:
             std::string getJSONValue(Value& value) {
                 std::stringstream ss;
-                PathSet ps;
+                NixStringContext ps;
                 printValueAsJSON(state, true, value, noPos, ss, ps);
                 return ss.str();
             }

src/libexpr/tests/value/context.cc

@@ -8,69 +8,62 @@
 
 namespace nix {
 
-// Testing of trivial expressions
+TEST(NixStringContextElemTest, empty_invalid) {
-struct NixStringContextElemTest : public LibExprTest {
-   const Store & store() const {
-       return *LibExprTest::store;
-   }
-};
-
-TEST_F(NixStringContextElemTest, empty_invalid) {
     EXPECT_THROW(
-        NixStringContextElem::parse(store(), ""),
+        NixStringContextElem::parse(""),
         BadNixStringContextElem);
 }
 
-TEST_F(NixStringContextElemTest, single_bang_invalid) {
+TEST(NixStringContextElemTest, single_bang_invalid) {
     EXPECT_THROW(
-        NixStringContextElem::parse(store(), "!"),
+        NixStringContextElem::parse("!"),
         BadNixStringContextElem);
 }
 
-TEST_F(NixStringContextElemTest, double_bang_invalid) {
+TEST(NixStringContextElemTest, double_bang_invalid) {
     EXPECT_THROW(
-        NixStringContextElem::parse(store(), "!!/"),
+        NixStringContextElem::parse("!!/"),
         BadStorePath);
 }
 
-TEST_F(NixStringContextElemTest, eq_slash_invalid) {
+TEST(NixStringContextElemTest, eq_slash_invalid) {
     EXPECT_THROW(
-        NixStringContextElem::parse(store(), "=/"),
+        NixStringContextElem::parse("=/"),
         BadStorePath);
 }
 
-TEST_F(NixStringContextElemTest, slash_invalid) {
+TEST(NixStringContextElemTest, slash_invalid) {
     EXPECT_THROW(
-        NixStringContextElem::parse(store(), "/"),
+        NixStringContextElem::parse("/"),
         BadStorePath);
 }
 
-TEST_F(NixStringContextElemTest, opaque) {
+TEST(NixStringContextElemTest, opaque) {
-    std::string_view opaque = "/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x";
+    std::string_view opaque = "g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x";
-    auto elem = NixStringContextElem::parse(store(), opaque);
+    auto elem = NixStringContextElem::parse(opaque);
     auto * p = std::get_if<NixStringContextElem::Opaque>(&elem);
     ASSERT_TRUE(p);
-    ASSERT_EQ(p->path, store().parseStorePath(opaque));
+    ASSERT_EQ(p->path, StorePath { opaque });
-    ASSERT_EQ(elem.to_string(store()), opaque);
+    ASSERT_EQ(elem.to_string(), opaque);
 }
 
-TEST_F(NixStringContextElemTest, drvDeep) {
+TEST(NixStringContextElemTest, drvDeep) {
-    std::string_view drvDeep = "=/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
+    std::string_view drvDeep = "=g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
-    auto elem = NixStringContextElem::parse(store(), drvDeep);
+    auto elem = NixStringContextElem::parse(drvDeep);
     auto * p = std::get_if<NixStringContextElem::DrvDeep>(&elem);
     ASSERT_TRUE(p);
-    ASSERT_EQ(p->drvPath, store().parseStorePath(drvDeep.substr(1)));
+    ASSERT_EQ(p->drvPath, StorePath { drvDeep.substr(1) });
-    ASSERT_EQ(elem.to_string(store()), drvDeep);
+    ASSERT_EQ(elem.to_string(), drvDeep);
 }
 
-TEST_F(NixStringContextElemTest, built) {
+TEST(NixStringContextElemTest, built) {
-    std::string_view built = "!foo!/nix/store/g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
+    std::string_view built = "!foo!g1w7hy3qg1w7hy3qg1w7hy3qg1w7hy3q-x.drv";
-    auto elem = NixStringContextElem::parse(store(), built);
+    auto elem = NixStringContextElem::parse(built);
     auto * p = std::get_if<NixStringContextElem::Built>(&elem);
     ASSERT_TRUE(p);
     ASSERT_EQ(p->output, "foo");
-    ASSERT_EQ(p->drvPath, store().parseStorePath(built.substr(5)));
+    ASSERT_EQ(p->drvPath, StorePath { built.substr(5) });
-    ASSERT_EQ(elem.to_string(store()), built);
+    ASSERT_EQ(elem.to_string(), built);
 }
 
 }
@@ -116,12 +109,12 @@ Gen<NixStringContextElem> Arbitrary<NixStringContextElem>::arbitrary()
 
 namespace nix {
 
-RC_GTEST_FIXTURE_PROP(
+RC_GTEST_PROP(
     NixStringContextElemTest,
     prop_round_rip,
     (const NixStringContextElem & o))
 {
-    RC_ASSERT(o == NixStringContextElem::parse(store(), o.to_string(store())));
+    RC_ASSERT(o == NixStringContextElem::parse(o.to_string()));
 }
 
 }

src/libexpr/value-to-json.cc

@@ -11,7 +11,7 @@
 namespace nix {
 using json = nlohmann::json;
 json printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, PathSet & context, bool copyToStore)
+    Value & v, const PosIdx pos, NixStringContext & context, bool copyToStore)
 {
     checkInterrupt();
 
@@ -95,13 +95,13 @@ json printValueAsJSON(EvalState & state, bool strict,
 }
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore)
+    Value & v, const PosIdx pos, std::ostream & str, NixStringContext & context, bool copyToStore)
 {
     str << printValueAsJSON(state, strict, v, pos, context, copyToStore);
 }
 
 json ExternalValueBase::printValueAsJSON(EvalState & state, bool strict,
-    PathSet & context, bool copyToStore) const
+    NixStringContext & context, bool copyToStore) const
 {
     state.debugThrowLastTrace(TypeError("cannot convert %1% to JSON", showType()));
 }

src/libexpr/value-to-json.hh

@@ -11,9 +11,9 @@
 namespace nix {
 
 nlohmann::json printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, PathSet & context, bool copyToStore = true);
+    Value & v, const PosIdx pos, NixStringContext & context, bool copyToStore = true);
 
 void printValueAsJSON(EvalState & state, bool strict,
-    Value & v, const PosIdx pos, std::ostream & str, PathSet & context, bool copyToStore = true);
+    Value & v, const PosIdx pos, std::ostream & str, NixStringContext & context, bool copyToStore = true);
 
 }

src/libexpr/value-to-xml.cc

@@ -18,7 +18,7 @@ static XMLAttrs singletonAttrs(const std::string & name, const std::string & val
 
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    Value & v, XMLWriter & doc, NixStringContext & context, PathSet & drvsSeen,
     const PosIdx pos);
 
 
@@ -32,7 +32,7 @@ static void posToXML(EvalState & state, XMLAttrs & xmlAttrs, const Pos & pos)
 
 
 static void showAttrs(EvalState & state, bool strict, bool location,
-    Bindings & attrs, XMLWriter & doc, PathSet & context, PathSet & drvsSeen)
+    Bindings & attrs, XMLWriter & doc, NixStringContext & context, PathSet & drvsSeen)
 {
     StringSet names;
 
@@ -54,7 +54,7 @@ static void showAttrs(EvalState & state, bool strict, bool location,
 
 
 static void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    Value & v, XMLWriter & doc, NixStringContext & context, PathSet & drvsSeen,
     const PosIdx pos)
 {
     checkInterrupt();
@@ -166,7 +166,7 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
 
 
 void ExternalValueBase::printValueAsXML(EvalState & state, bool strict,
-    bool location, XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+    bool location, XMLWriter & doc, NixStringContext & context, PathSet & drvsSeen,
     const PosIdx pos) const
 {
     doc.writeEmptyElement("unevaluated");
@@ -174,7 +174,7 @@ void ExternalValueBase::printValueAsXML(EvalState & state, bool strict,
 
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context, const PosIdx pos)
+    Value & v, std::ostream & out, NixStringContext & context, const PosIdx pos)
 {
     XMLWriter doc(true, out);
     XMLOpenElement root(doc, "expr");

src/libexpr/value-to-xml.hh

@@ -10,6 +10,6 @@
 namespace nix {
 
 void printValueAsXML(EvalState & state, bool strict, bool location,
-    Value & v, std::ostream & out, PathSet & context, const PosIdx pos);
+    Value & v, std::ostream & out, NixStringContext & context, const PosIdx pos);
 
 }

src/libexpr/value.hh

@@ -101,7 +101,7 @@ class ExternalValueBase
      * Coerce the value to a string. Defaults to uncoercable, i.e. throws an
      * error.
      */
-    virtual std::string coerceToString(const Pos & pos, PathSet & context, bool copyMore, bool copyToStore) const;
+    virtual std::string coerceToString(const Pos & pos, NixStringContext & context, bool copyMore, bool copyToStore) const;
 
     /**
      * Compare to another value of the same type. Defaults to uncomparable,
@@ -113,13 +113,13 @@ class ExternalValueBase
      * Print the value as JSON. Defaults to unconvertable, i.e. throws an error
      */
     virtual nlohmann::json printValueAsJSON(EvalState & state, bool strict,
-        PathSet & context, bool copyToStore = true) const;
+        NixStringContext & context, bool copyToStore = true) const;
 
     /**
      * Print the value as XML. Defaults to unevaluated
      */
     virtual void printValueAsXML(EvalState & state, bool strict, bool location,
-        XMLWriter & doc, PathSet & context, PathSet & drvsSeen,
+        XMLWriter & doc, NixStringContext & context, PathSet & drvsSeen,
         const PosIdx pos) const;
 
     virtual ~ExternalValueBase()
@@ -269,9 +269,9 @@ public:
 
     void mkString(std::string_view s);
 
-    void mkString(std::string_view s, const PathSet & context);
+    void mkString(std::string_view s, const NixStringContext & context);
 
-    void mkStringMove(const char * s, const PathSet & context);
+    void mkStringMove(const char * s, const NixStringContext & context);
 
     inline void mkString(const Symbol & s)
     {
@@ -400,8 +400,6 @@ public:
      */
     bool isTrivial() const;
 
-    NixStringContext getContext(const Store &);
-
     auto listItems()
     {
         struct ListIterable

src/libexpr/value/context.cc

@@ -1,11 +1,10 @@
 #include "value/context.hh"
-#include "store-api.hh"
 
 #include <optional>
 
 namespace nix {
 
-NixStringContextElem NixStringContextElem::parse(const Store & store, std::string_view s0)
+NixStringContextElem NixStringContextElem::parse(std::string_view s0)
 {
     std::string_view s = s0;
 
@@ -25,41 +24,41 @@ NixStringContextElem NixStringContextElem::parse(const Store & store, std::strin
                 "String content element beginning with '!' should have a second '!'");
         }
         return NixStringContextElem::Built {
-            .drvPath = store.parseStorePath(s.substr(index + 1)),
+            .drvPath = StorePath { s.substr(index + 1) },
             .output = std::string(s.substr(0, index)),
         };
     }
     case '=': {
         return NixStringContextElem::DrvDeep {
-            .drvPath = store.parseStorePath(s.substr(1)),
+            .drvPath = StorePath { s.substr(1) },
         };
     }
     default: {
         return NixStringContextElem::Opaque {
-            .path = store.parseStorePath(s),
+            .path = StorePath { s },
         };
     }
     }
 }
 
-std::string NixStringContextElem::to_string(const Store & store) const {
+std::string NixStringContextElem::to_string() const {
     return std::visit(overloaded {
         [&](const NixStringContextElem::Built & b) {
             std::string res;
             res += '!';
             res += b.output;
             res += '!';
-            res += store.printStorePath(b.drvPath);
+            res += b.drvPath.to_string();
             return res;
         },
         [&](const NixStringContextElem::DrvDeep & d) {
             std::string res;
             res += '=';
-            res += store.printStorePath(d.drvPath);
+            res += d.drvPath.to_string();
             return res;
         },
         [&](const NixStringContextElem::Opaque & o) {
-            return store.printStorePath(o.path);
+            return std::string { o.path.to_string() };
         },
     }, raw());
 }

src/libexpr/value/context.hh

@@ -26,8 +26,6 @@ public:
     }
 };
 
-class Store;
-
 /**
  * Plain opaque path to some store object.
  *
@@ -80,12 +78,15 @@ struct NixStringContextElem : _NixStringContextElem_Raw {
     using DrvDeep = NixStringContextElem_DrvDeep;
     using Built = NixStringContextElem_Built;
 
-    inline const Raw & raw() const {
+    inline const Raw & raw() const & {
         return static_cast<const Raw &>(*this);
     }
-    inline Raw & raw() {
+    inline Raw & raw() & {
         return static_cast<Raw &>(*this);
     }
+    inline Raw && raw() && {
+        return static_cast<Raw &&>(*this);
+    }
 
     /**
      * Decode a context string, one of:
@@ -93,10 +94,10 @@ struct NixStringContextElem : _NixStringContextElem_Raw {
      * - ‘=<path>’
      * - ‘!<name>!<path>’
      */
-    static NixStringContextElem parse(const Store & store, std::string_view s);
+    static NixStringContextElem parse(std::string_view s);
-    std::string to_string(const Store & store) const;
+    std::string to_string() const;
 };
 
-typedef std::vector<NixStringContextElem> NixStringContext;
+typedef std::set<NixStringContextElem> NixStringContext;
 
 }

src/libfetchers/fetchers.cc

@@ -210,7 +210,13 @@ StorePath Input::computeStorePath(Store & store) const
     auto narHash = getNarHash();
     if (!narHash)
         throw Error("cannot compute store path for unlocked input '%s'", to_string());
-    return store.makeFixedOutputPath(FileIngestionMethod::Recursive, *narHash, getName());
+    return store.makeFixedOutputPath(getName(), FixedOutputInfo {
+        .hash = {
+            .method = FileIngestionMethod::Recursive,
+            .hash = *narHash,
+        },
+        .references = {},
+    });
 }
 
 std::string Input::getType() const

src/libfetchers/tarball.cc

@@ -71,15 +71,19 @@ DownloadFileResult downloadFile(
         dumpString(res.data, sink);
         auto hash = hashString(htSHA256, res.data);
         ValidPathInfo info {
-            store->makeFixedOutputPath(FileIngestionMethod::Flat, hash, name),
+            *store,
+            name,
+            FixedOutputInfo {
+                .hash = {
+                    .method = FileIngestionMethod::Flat,
+                    .hash = hash,
+                },
+                .references = {},
+            },
             hashString(htSHA256, sink.s),
         };
         info.narSize = sink.s.size();
-        info.ca = FixedOutputHash {
+        auto source = StringSource { sink.s };
-            .method = FileIngestionMethod::Flat,
-            .hash = hash,
-        };
-        auto source = StringSource(sink.s);
         store->addToStore(info, source, NoRepair, NoCheckSigs);
         storePath = std::move(info.path);
     }

src/libmain/shared.cc

@@ -10,7 +10,6 @@
 #include <cctype>
 #include <exception>
 #include <iostream>
-#include <mutex>
 
 #include <cstdlib>
 #include <sys/time.h>
@@ -20,16 +19,9 @@
 #ifdef __linux__
 #include <features.h>
 #endif
-#ifdef __GLIBC__
-#include <gnu/lib-names.h>
-#include <nss.h>
-#include <dlfcn.h>
-#endif
 
 #include <openssl/crypto.h>
 
-#include <sodium.h>
-
 
 namespace nix {
 
@@ -115,57 +107,6 @@ std::string getArg(const std::string & opt,
     return *i;
 }
 
-
-#if OPENSSL_VERSION_NUMBER < 0x10101000L
-/* OpenSSL is not thread-safe by default - it will randomly crash
-   unless the user supplies a mutex locking function. So let's do
-   that. */
-static std::vector<std::mutex> opensslLocks;
-
-static void opensslLockCallback(int mode, int type, const char * file, int line)
-{
-    if (mode & CRYPTO_LOCK)
-        opensslLocks[type].lock();
-    else
-        opensslLocks[type].unlock();
-}
-#endif
-
-static std::once_flag dns_resolve_flag;
-
-static void preloadNSS() {
-    /* builtin:fetchurl can trigger a DNS lookup, which with glibc can trigger a dynamic library load of
-       one of the glibc NSS libraries in a sandboxed child, which will fail unless the library's already
-       been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to
-       load its lookup libraries in the parent before any child gets a chance to. */
-    std::call_once(dns_resolve_flag, []() {
-#ifdef __GLIBC__
-        /* On linux, glibc will run every lookup through the nss layer.
-         * That means every lookup goes, by default, through nscd, which acts as a local
-         * cache.
-         * Because we run builds in a sandbox, we also remove access to nscd otherwise
-         * lookups would leak into the sandbox.
-         *
-         * But now we have a new problem, we need to make sure the nss_dns backend that
-         * does the dns lookups when nscd is not available is loaded or available.
-         *
-         * We can't make it available without leaking nix's environment, so instead we'll
-         * load the backend, and configure nss so it does not try to run dns lookups
-         * through nscd.
-         *
-         * This is technically only used for builtins:fetch* functions so we only care
-         * about dns.
-         *
-         * All other platforms are unaffected.
-         */
-        if (!dlopen(LIBNSS_DNS_SO, RTLD_NOW))
-            warn("unable to load nss_dns backend");
-        // FIXME: get hosts entry from nsswitch.conf.
-        __nss_configure_lookup("hosts", "files dns");
-#endif
-    });
-}
-
 static void sigHandler(int signo) { }
 
 
@@ -177,16 +118,7 @@ void initNix()
     std::cerr.rdbuf()->pubsetbuf(buf, sizeof(buf));
 #endif
 
-#if OPENSSL_VERSION_NUMBER < 0x10101000L
+    initLibStore();
-    /* Initialise OpenSSL locking. */
-    opensslLocks = std::vector<std::mutex>(CRYPTO_num_locks());
-    CRYPTO_set_locking_callback(opensslLockCallback);
-#endif
-
-    if (sodium_init() == -1)
-        throw Error("could not initialise libsodium");
-
-    loadConfFile();
 
     startSignalHandlerThread();
 
@@ -223,7 +155,10 @@ void initNix()
     if (sigaction(SIGTRAP, &act, 0)) throw SysError("handling SIGTRAP");
 #endif
 
-    /* Register a SIGSEGV handler to detect stack overflows. */
+    /* Register a SIGSEGV handler to detect stack overflows.
+       Why not initLibExpr()? initGC() is essentially that, but
+       detectStackOverflow is not an instance of the init function concept, as
+       it may have to be invoked more than once per process. */
     detectStackOverflow();
 
     /* There is no privacy in the Nix system ;-)  At least not for
@@ -236,16 +171,6 @@ void initNix()
     gettimeofday(&tv, 0);
     srandom(tv.tv_usec);
 
-    /* On macOS, don't use the per-session TMPDIR (as set e.g. by
-       sshd). This breaks build users because they don't have access
-       to the TMPDIR, in particular in ‘nix-store --serve’. */
-#if __APPLE__
-    if (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
-        unsetenv("TMPDIR");
-#endif
-
-    preloadNSS();
-    initLibStore();
 }
 
 

src/libstore/binary-cache-store.cc

@@ -306,11 +306,22 @@ StorePath BinaryCacheStore::addToStoreFromDump(Source & dump, std::string_view n
         unsupported("addToStoreFromDump");
     return addToStoreCommon(dump, repair, CheckSigs, [&](HashResult nar) {
         ValidPathInfo info {
-            makeFixedOutputPath(method, nar.first, name, references),
+            *this,
+            name,
+            FixedOutputInfo {
+                .hash = {
+                    .method = method,
+                    .hash = nar.first,
+                },
+                .references = {
+                    .others = references,
+                    // caller is not capable of creating a self-reference, because this is content-addressed without modulus
+                    .self = false,
+                },
+            },
             nar.first,
         };
         info.narSize = nar.second;
-        info.references = references;
         return info;
     })->path;
 }
@@ -414,15 +425,22 @@ StorePath BinaryCacheStore::addToStore(
     });
     return addToStoreCommon(*source, repair, CheckSigs, [&](HashResult nar) {
         ValidPathInfo info {
-            makeFixedOutputPath(method, h, name, references),
+            *this,
+            name,
+            FixedOutputInfo {
+                .hash = {
+                    .method = method,
+                    .hash = h,
+                },
+                .references = {
+                    .others = references,
+                    // caller is not capable of creating a self-reference, because this is content-addressed without modulus
+                    .self = false,
+                },
+            },
             nar.first,
         };
         info.narSize = nar.second;
-        info.references = references;
-        info.ca = FixedOutputHash {
-            .method = method,
-            .hash = h,
-        };
         return info;
     })->path;
 }
@@ -434,7 +452,7 @@ StorePath BinaryCacheStore::addTextToStore(
     RepairFlag repair)
 {
     auto textHash = hashString(htSHA256, s);
-    auto path = makeTextPath(name, textHash, references);
+    auto path = makeTextPath(name, TextInfo { { textHash }, references });
 
     if (!repair && isValidPath(path))
         return path;
@@ -443,10 +461,16 @@ StorePath BinaryCacheStore::addTextToStore(
     dumpString(s, sink);
     StringSource source(sink.s);
     return addToStoreCommon(source, repair, CheckSigs, [&](HashResult nar) {
-        ValidPathInfo info { path, nar.first };
+        ValidPathInfo info {
+            *this,
+            std::string { name },
+            TextInfo {
+                { .hash = textHash },
+                references,
+            },
+            nar.first,
+        };
         info.narSize = nar.second;
-        info.ca = TextHash { textHash };
-        info.references = references;
         return info;
     })->path;
 }

src/libstore/build-result.hh

@@ -83,16 +83,11 @@ struct BuildResult
      */
     bool isNonDeterministic = false;
 
-    /**
-     * The derivation we built or the store path we substituted.
-     */
-    DerivedPath path;
-
     /**
      * For derivations, a mapping from the names of the wanted outputs
      * to actual paths.
      */
-    DrvOutputs builtOutputs;
+    SingleDrvOutputs builtOutputs;
 
     /**
      * The start/stop times of the build (or one of the rounds, if it
@@ -116,4 +111,15 @@ struct BuildResult
     }
 };
 
+/**
+ * A `BuildResult` together with its "primary key".
+ */
+struct KeyedBuildResult : BuildResult
+{
+    /**
+     * The derivation we built or the store path we substituted.
+     */
+    DerivedPath path;
+};
+
 }

src/libstore/build/derivation-goal.cc

@@ -145,8 +145,20 @@ void DerivationGoal::work()
 void DerivationGoal::addWantedOutputs(const OutputsSpec & outputs)
 {
     auto newWanted = wantedOutputs.union_(outputs);
+    switch (needRestart) {
+    case NeedRestartForMoreOutputs::OutputsUnmodifedDontNeed:
         if (!newWanted.isSubsetOf(wantedOutputs))
-        needRestart = true;
+            needRestart = NeedRestartForMoreOutputs::OutputsAddedDoNeed;
+        break;
+    case NeedRestartForMoreOutputs::OutputsAddedDoNeed:
+        /* No need to check whether we added more outputs, because a
+           restart is already queued up. */
+        break;
+    case NeedRestartForMoreOutputs::BuildInProgressWillNotNeed:
+        /* We are already building all outputs, so it doesn't matter if
+           we now want more. */
+        break;
+    };
     wantedOutputs = newWanted;
 }
 
@@ -297,12 +309,29 @@ void DerivationGoal::outputsSubstitutionTried()
         In particular, it may be the case that the hole in the closure is
         an output of the current derivation, which causes a loop if retried.
      */
-    if (nrIncompleteClosure > 0 && nrIncompleteClosure == nrFailed) retrySubstitution = true;
+    {
+        bool substitutionFailed =
+            nrIncompleteClosure > 0 &&
+            nrIncompleteClosure == nrFailed;
+        switch (retrySubstitution) {
+        case RetrySubstitution::NoNeed:
+            if (substitutionFailed)
+                retrySubstitution = RetrySubstitution::YesNeed;
+            break;
+        case RetrySubstitution::YesNeed:
+            // Should not be able to reach this state from here.
+            assert(false);
+            break;
+        case RetrySubstitution::AlreadyRetried:
+            debug("substitution failed again, but we already retried once. Not retrying again.");
+            break;
+        }
+    }
 
     nrFailed = nrNoSubstituters = nrIncompleteClosure = 0;
 
-    if (needRestart) {
+    if (needRestart == NeedRestartForMoreOutputs::OutputsAddedDoNeed) {
-        needRestart = false;
+        needRestart = NeedRestartForMoreOutputs::OutputsUnmodifedDontNeed;
         haveDerivation();
         return;
     }
@@ -330,6 +359,10 @@ void DerivationGoal::outputsSubstitutionTried()
    produced using a substitute.  So we have to build instead. */
 void DerivationGoal::gaveUpOnSubstitution()
 {
+    /* At this point we are building all outputs, so if more are wanted there
+       is no need to restart. */
+    needRestart = NeedRestartForMoreOutputs::BuildInProgressWillNotNeed;
+
     /* The inputs must be built before we can build this goal. */
     inputDrvOutputs.clear();
     if (useDerivation)
@@ -451,8 +484,8 @@ void DerivationGoal::inputsRealised()
         return;
     }
 
-    if (retrySubstitution && !retriedSubstitution) {
+    if (retrySubstitution == RetrySubstitution::YesNeed) {
-        retriedSubstitution = true;
+        retrySubstitution = RetrySubstitution::AlreadyRetried;
         haveDerivation();
         return;
     }
@@ -570,8 +603,6 @@ void DerivationGoal::inputsRealised()
        build hook. */
     state = &DerivationGoal::tryToBuild;
     worker.wakeUp(shared_from_this());
-
-    buildResult = BuildResult { .path = buildResult.path };
 }
 
 void DerivationGoal::started()
@@ -982,7 +1013,7 @@ void DerivationGoal::resolvedFinished()
     auto resolvedDrv = *resolvedDrvGoal->drv;
     auto & resolvedResult = resolvedDrvGoal->buildResult;
 
-    DrvOutputs builtOutputs;
+    SingleDrvOutputs builtOutputs;
 
     if (resolvedResult.success()) {
         auto resolvedHashes = staticOutputHashes(worker.store, resolvedDrv);
@@ -1008,7 +1039,7 @@ void DerivationGoal::resolvedFinished()
                     worker.store.printStorePath(drvPath), wantedOutput);
 
             auto realisation = [&]{
-              auto take1 = get(resolvedResult.builtOutputs, DrvOutput { *resolvedHash, wantedOutput });
+              auto take1 = get(resolvedResult.builtOutputs, wantedOutput);
               if (take1) return *take1;
 
               /* The above `get` should work. But sateful tracking of
@@ -1033,7 +1064,7 @@ void DerivationGoal::resolvedFinished()
                 worker.store.registerDrvOutput(newRealisation);
             }
             outputPaths.insert(realisation.outPath);
-            builtOutputs.emplace(realisation.id, realisation);
+            builtOutputs.emplace(wantedOutput, realisation);
         }
 
         runPostBuildHook(
@@ -1158,7 +1189,7 @@ HookReply DerivationGoal::tryBuildHook()
 }
 
 
-DrvOutputs DerivationGoal::registerOutputs()
+SingleDrvOutputs DerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
        as valid (by doing `nix-store --import').  If so we don't have
@@ -1320,7 +1351,7 @@ OutputPathMap DerivationGoal::queryDerivationOutputMap()
 }
 
 
-std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
+std::pair<bool, SingleDrvOutputs> DerivationGoal::checkPathValidity()
 {
     if (!drv->type().isPure()) return { false, {} };
 
@@ -1333,7 +1364,7 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
             return static_cast<StringSet>(names);
         },
     }, wantedOutputs.raw());
-    DrvOutputs validOutputs;
+    SingleDrvOutputs validOutputs;
 
     for (auto & i : queryPartialDerivationOutputMap()) {
         auto initialOutput = get(initialOutputs, i.first);
@@ -1376,7 +1407,7 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
             }
         }
         if (info.wanted && info.known && info.known->isValid())
-            validOutputs.emplace(drvOutput, Realisation { drvOutput, info.known->path });
+            validOutputs.emplace(i.first, Realisation { drvOutput, info.known->path });
     }
 
     // If we requested all the outputs, we are always fine.
@@ -1400,7 +1431,7 @@ std::pair<bool, DrvOutputs> DerivationGoal::checkPathValidity()
 }
 
 
-DrvOutputs DerivationGoal::assertPathValidity()
+SingleDrvOutputs DerivationGoal::assertPathValidity()
 {
     auto [allValid, validOutputs] = checkPathValidity();
     if (!allValid)
@@ -1411,7 +1442,7 @@ DrvOutputs DerivationGoal::assertPathValidity()
 
 void DerivationGoal::done(
     BuildResult::Status status,
-    DrvOutputs builtOutputs,
+    SingleDrvOutputs builtOutputs,
     std::optional<Error> ex)
 {
     buildResult.status = status;
@@ -1452,12 +1483,28 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
 {
     Goal::waiteeDone(waitee, result);
 
-    if (waitee->buildResult.success())
+    if (!useDerivation) return;
-        if (auto bfd = std::get_if<DerivedPath::Built>(&waitee->buildResult.path))
+    auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
-            for (auto & [output, realisation] : waitee->buildResult.builtOutputs)
+
+    auto * dg = dynamic_cast<DerivationGoal *>(&*waitee);
+    if (!dg) return;
+
+    auto outputs = fullDrv.inputDrvs.find(dg->drvPath);
+    if (outputs == fullDrv.inputDrvs.end()) return;
+
+    for (auto & outputName : outputs->second) {
+        auto buildResult = dg->getBuildResult(DerivedPath::Built {
+            .drvPath = dg->drvPath,
+            .outputs = OutputsSpec::Names { outputName },
+        });
+        if (buildResult.success()) {
+            auto i = buildResult.builtOutputs.find(outputName);
+            if (i != buildResult.builtOutputs.end())
                 inputDrvOutputs.insert_or_assign(
-                    { bfd->drvPath, output.outputName },
+                    { dg->drvPath, outputName },
-                    realisation.outPath);
+                    i->second.outPath);
+        }
+    }
 }
 
 }

src/libstore/build/derivation-goal.hh

@@ -78,22 +78,58 @@ struct DerivationGoal : public Goal
      */
     std::map<std::pair<StorePath, std::string>, StorePath> inputDrvOutputs;
 
+    /**
+     * See `needRestart`; just for that field.
+     */
+    enum struct NeedRestartForMoreOutputs {
+        /**
+         * The goal state machine is progressing based on the current value of
+         * `wantedOutputs. No actions are needed.
+         */
+        OutputsUnmodifedDontNeed,
+        /**
+         * `wantedOutputs` has been extended, but the state machine is
+         * proceeding according to its old value, so we need to restart.
+         */
+        OutputsAddedDoNeed,
+        /**
+         * The goal state machine has progressed to the point of doing a build,
+         * in which case all outputs will be produced, so extensions to
+         * `wantedOutputs` no longer require a restart.
+         */
+        BuildInProgressWillNotNeed,
+    };
+
     /**
      * Whether additional wanted outputs have been added.
      */
-    bool needRestart = false;
+    NeedRestartForMoreOutputs needRestart = NeedRestartForMoreOutputs::OutputsUnmodifedDontNeed;
+
+    /**
+     * See `retrySubstitution`; just for that field.
+     */
+    enum RetrySubstitution {
+        /**
+         * No issues have yet arose, no need to restart.
+         */
+        NoNeed,
+        /**
+         * Something failed and there is an incomplete closure. Let's retry
+         * substituting.
+         */
+        YesNeed,
+        /**
+         * We are current or have already retried substitution, and whether or
+         * not something goes wrong we will not retry again.
+         */
+        AlreadyRetried,
+    };
 
     /**
      * Whether to retry substituting the outputs after building the
      * inputs. This is done in case of an incomplete closure.
      */
-    bool retrySubstitution = false;
+    RetrySubstitution retrySubstitution = RetrySubstitution::NoNeed;
-
-    /**
-     * Whether we've retried substitution, in which case we won't try
-     * again.
-     */
-    bool retriedSubstitution = false;
 
     /**
      * The derivation stored at drvPath.
@@ -217,7 +253,7 @@ struct DerivationGoal : public Goal
      * Check that the derivation outputs all exist and register them
      * as valid.
      */
-    virtual DrvOutputs registerOutputs();
+    virtual SingleDrvOutputs registerOutputs();
 
     /**
      * Open a log file and a pipe to it.
@@ -270,17 +306,17 @@ struct DerivationGoal : public Goal
      * Update 'initialOutputs' to determine the current status of the
      * outputs of the derivation. Also returns a Boolean denoting
      * whether all outputs are valid and non-corrupt, and a
-     * 'DrvOutputs' structure containing the valid and wanted
+     * 'SingleDrvOutputs' structure containing the valid and wanted
      * outputs.
      */
-    std::pair<bool, DrvOutputs> checkPathValidity();
+    std::pair<bool, SingleDrvOutputs> checkPathValidity();
 
     /**
      * Aborts if any output is not valid or corrupt, and otherwise
-     * returns a 'DrvOutputs' structure containing the wanted
+     * returns a 'SingleDrvOutputs' structure containing the wanted
      * outputs.
      */
-    DrvOutputs assertPathValidity();
+    SingleDrvOutputs assertPathValidity();
 
     /**
      * Forcibly kill the child process, if any.
@@ -293,7 +329,7 @@ struct DerivationGoal : public Goal
 
     void done(
         BuildResult::Status status,
-        DrvOutputs builtOutputs = {},
+        SingleDrvOutputs builtOutputs = {},
         std::optional<Error> ex = {});
 
     void waiteeDone(GoalPtr waitee, ExitCode result) override;

src/libstore/build/entry-points.cc

@@ -10,16 +10,8 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
     Worker worker(*this, evalStore ? *evalStore : *this);
 
     Goals goals;
-    for (const auto & br : reqs) {
+    for (auto & br : reqs)
-        std::visit(overloaded {
+        goals.insert(worker.makeGoal(br, buildMode));
-            [&](const DerivedPath::Built & bfd) {
-                goals.insert(worker.makeDerivationGoal(bfd.drvPath, bfd.outputs, buildMode));
-            },
-            [&](const DerivedPath::Opaque & bo) {
-                goals.insert(worker.makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair));
-            },
-        }, br.raw());
-    }
 
     worker.run(goals);
 
@@ -47,7 +39,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
     }
 }
 
-std::vector<BuildResult> Store::buildPathsWithResults(
+std::vector<KeyedBuildResult> Store::buildPathsWithResults(
     const std::vector<DerivedPath> & reqs,
     BuildMode buildMode,
     std::shared_ptr<Store> evalStore)
@@ -55,23 +47,23 @@ std::vector<BuildResult> Store::buildPathsWithResults(
     Worker worker(*this, evalStore ? *evalStore : *this);
 
     Goals goals;
-    for (const auto & br : reqs) {
+    std::vector<std::pair<const DerivedPath &, GoalPtr>> state;
-        std::visit(overloaded {
+
-            [&](const DerivedPath::Built & bfd) {
+    for (const auto & req : reqs) {
-                goals.insert(worker.makeDerivationGoal(bfd.drvPath, bfd.outputs, buildMode));
+        auto goal = worker.makeGoal(req, buildMode);
-            },
+        goals.insert(goal);
-            [&](const DerivedPath::Opaque & bo) {
+        state.push_back({req, goal});
-                goals.insert(worker.makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair));
-            },
-        }, br.raw());
     }
 
     worker.run(goals);
 
-    std::vector<BuildResult> results;
+    std::vector<KeyedBuildResult> results;
 
-    for (auto & i : goals)
+    for (auto & [req, goalPtr] : state)
-        results.push_back(i->buildResult);
+        results.emplace_back(KeyedBuildResult {
+            goalPtr->getBuildResult(req),
+            /* .path = */ req,
+        });
 
     return results;
 }
@@ -84,15 +76,14 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
 
     try {
         worker.run(Goals{goal});
-        return goal->buildResult;
+        return goal->getBuildResult(DerivedPath::Built {
+            .drvPath = drvPath,
+            .outputs = OutputsSpec::All {},
+        });
     } catch (Error & e) {
         return BuildResult {
             .status = BuildResult::MiscFailure,
             .errorMsg = e.msg(),
-            .path = DerivedPath::Built {
-                .drvPath = drvPath,
-                .outputs = OutputsSpec::All { },
-            },
         };
     };
 }

src/libstore/build/goal.cc

@@ -11,6 +11,29 @@ bool CompareGoalPtrs::operator() (const GoalPtr & a, const GoalPtr & b) const {
 }
 
 
+BuildResult Goal::getBuildResult(const DerivedPath & req) {
+    BuildResult res { buildResult };
+
+    if (auto pbp = std::get_if<DerivedPath::Built>(&req)) {
+        auto & bp = *pbp;
+
+        /* Because goals are in general shared between derived paths
+           that share the same derivation, we need to filter their
+           results to get back just the results we care about.
+         */
+
+        for (auto it = res.builtOutputs.begin(); it != res.builtOutputs.end();) {
+            if (bp.outputs.contains(it->first))
+                ++it;
+            else
+                it = res.builtOutputs.erase(it);
+        }
+    }
+
+    return res;
+}
+
+
 void addToWeakGoals(WeakGoals & goals, GoalPtr p)
 {
     if (goals.find(p) != goals.end())

src/libstore/build/goal.hh

@@ -81,11 +81,26 @@ struct Goal : public std::enable_shared_from_this<Goal>
      */
     ExitCode exitCode = ecBusy;
 
+protected:
     /**
      * Build result.
      */
     BuildResult buildResult;
 
+public:
+
+    /**
+     * Project a `BuildResult` with just the information that pertains
+     * to the given request.
+     *
+     * In general, goals may be aliased between multiple requests, and
+     * the stored `BuildResult` has information for the union of all
+     * requests. We don't want to leak what the other request are for
+     * sake of both privacy and determinism, and this "safe accessor"
+     * ensures we don't.
+     */
+    BuildResult getBuildResult(const DerivedPath &);
+
     /**
      * Exception containing an error message, if any.
      */
@@ -93,7 +108,6 @@ struct Goal : public std::enable_shared_from_this<Goal>
 
     Goal(Worker & worker, DerivedPath path)
         : worker(worker)
-        , buildResult { .path = std::move(path) }
     { }
 
     virtual ~Goal()

src/libstore/build/local-derivation-goal.cc

@@ -1335,7 +1335,7 @@ struct RestrictedStore : public virtual RestrictedStoreConfig, public virtual Lo
                 result.rethrow();
     }
 
-    std::vector<BuildResult> buildPathsWithResults(
+    std::vector<KeyedBuildResult> buildPathsWithResults(
         const std::vector<DerivedPath> & paths,
         BuildMode buildMode = bmNormal,
         std::shared_ptr<Store> evalStore = nullptr) override
@@ -2174,7 +2174,7 @@ void LocalDerivationGoal::runChild()
 }
 
 
-DrvOutputs LocalDerivationGoal::registerOutputs()
+SingleDrvOutputs LocalDerivationGoal::registerOutputs()
 {
     /* When using a build hook, the build hook can register the output
        as valid (by doing `nix-store --import').  If so we don't have
@@ -2395,27 +2395,26 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             }
         };
 
-        auto rewriteRefs = [&]() -> std::pair<bool, StorePathSet> {
+        auto rewriteRefs = [&]() -> StoreReferences {
             /* In the CA case, we need the rewritten refs to calculate the
                final path, therefore we look for a *non-rewritten
                self-reference, and use a bool rather try to solve the
                computationally intractable fixed point. */
-            std::pair<bool, StorePathSet> res {
+            StoreReferences res {
-                false,
+                .self = false,
-                {},
             };
             for (auto & r : references) {
                 auto name = r.name();
                 auto origHash = std::string { r.hashPart() };
                 if (r == *scratchPath) {
-                    res.first = true;
+                    res.self = true;
                 } else if (auto outputRewrite = get(outputRewrites, origHash)) {
                     std::string newRef = *outputRewrite;
                     newRef += '-';
                     newRef += name;
-                    res.second.insert(StorePath { newRef });
+                    res.others.insert(StorePath { newRef });
                 } else {
-                    res.second.insert(r);
+                    res.others.insert(r);
                 }
             }
             return res;
@@ -2448,18 +2447,22 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
                 break;
             }
             auto got = caSink.finish().first;
-            auto refs = rewriteRefs();
+            ValidPathInfo newInfo0 {
-
+                worker.store,
-            auto finalPath = worker.store.makeFixedOutputPath(
-                    outputHash.method,
-                    got,
                 outputPathName(drv->name, outputName),
-                    refs.second,
+                FixedOutputInfo {
-                    refs.first);
+                    .hash = {
-            if (*scratchPath != finalPath) {
+                        .method = outputHash.method,
+                        .hash = got,
+                    },
+                    .references = rewriteRefs(),
+                },
+                Hash::dummy,
+            };
+            if (*scratchPath != newInfo0.path) {
                 // Also rewrite the output path
                 auto source = sinkToSource([&](Sink & nextSink) {
-                    RewritingSink rsink2(oldHashPart, std::string(finalPath.hashPart()), nextSink);
+                    RewritingSink rsink2(oldHashPart, std::string(newInfo0.path.hashPart()), nextSink);
                     dumpPath(actualPath, rsink2);
                     rsink2.flush();
                 });
@@ -2470,19 +2473,8 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             }
 
             HashResult narHashAndSize = hashPath(htSHA256, actualPath);
-            ValidPathInfo newInfo0 {
+            newInfo0.narHash = narHashAndSize.first;
-                finalPath,
-                narHashAndSize.first,
-            };
-
             newInfo0.narSize = narHashAndSize.second;
-            newInfo0.ca = FixedOutputHash {
-                .method = outputHash.method,
-                .hash = got,
-            };
-            newInfo0.references = refs.second;
-            if (refs.first)
-                newInfo0.references.insert(newInfo0.path);
 
             assert(newInfo0.ca);
             return newInfo0;
@@ -2504,8 +2496,8 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
                 ValidPathInfo newInfo0 { requiredFinalPath, narHashAndSize.first };
                 newInfo0.narSize = narHashAndSize.second;
                 auto refs = rewriteRefs();
-                newInfo0.references = refs.second;
+                newInfo0.references = std::move(refs.others);
-                if (refs.first)
+                if (refs.self)
                     newInfo0.references.insert(newInfo0.path);
                 return newInfo0;
             },
@@ -2519,7 +2511,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
                 /* Check wanted hash */
                 const Hash & wanted = dof.hash.hash;
                 assert(newInfo0.ca);
-                auto got = getContentAddressHash(*newInfo0.ca);
+                auto got = newInfo0.ca->getHash();
                 if (wanted != got) {
                     /* Throw an error after registering the path as
                        valid. */
@@ -2691,7 +2683,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
        means it's safe to link the derivation to the output hash. We must do
        that for floating CA derivations, which otherwise couldn't be cached,
        but it's fine to do in all cases. */
-    DrvOutputs builtOutputs;
+    SingleDrvOutputs builtOutputs;
 
     for (auto & [outputName, newInfo] : infos) {
         auto oldinfo = get(initialOutputs, outputName);
@@ -2710,7 +2702,7 @@ DrvOutputs LocalDerivationGoal::registerOutputs()
             worker.store.registerDrvOutput(thisRealisation);
         }
         if (wantedOutputs.contains(outputName))
-            builtOutputs.emplace(thisRealisation.id, thisRealisation);
+            builtOutputs.emplace(outputName, thisRealisation);
     }
 
     return builtOutputs;

src/libstore/build/local-derivation-goal.hh

@@ -237,7 +237,7 @@ struct LocalDerivationGoal : public DerivationGoal
      * Check that the derivation outputs all exist and register them
      * as valid.
      */
-    DrvOutputs registerOutputs() override;
+    SingleDrvOutputs registerOutputs() override;
 
     void signRealisation(Realisation &) override;
 

src/libstore/build/substitution-goal.cc

@@ -95,7 +95,9 @@ void PathSubstitutionGoal::tryNext()
     subs.pop_front();
 
     if (ca) {
-        subPath = sub->makeFixedOutputPathFromCA(storePath.name(), *ca);
+        subPath = sub->makeFixedOutputPathFromCA(
+            std::string { storePath.name() },
+            ContentAddressWithReferences::withoutRefs(*ca));
         if (sub->storeDir == worker.store.storeDir)
             assert(subPath == storePath);
     } else if (sub->storeDir != worker.store.storeDir) {

src/libstore/build/worker.cc

@@ -92,6 +92,7 @@ std::shared_ptr<PathSubstitutionGoal> Worker::makePathSubstitutionGoal(const Sto
     return goal;
 }
 
+
 std::shared_ptr<DrvOutputSubstitutionGoal> Worker::makeDrvOutputSubstitutionGoal(const DrvOutput& id, RepairFlag repair, std::optional<ContentAddress> ca)
 {
     std::weak_ptr<DrvOutputSubstitutionGoal> & goal_weak = drvOutputSubstitutionGoals[id];
@@ -104,6 +105,20 @@ std::shared_ptr<DrvOutputSubstitutionGoal> Worker::makeDrvOutputSubstitutionGoal
     return goal;
 }
 
+
+GoalPtr Worker::makeGoal(const DerivedPath & req, BuildMode buildMode)
+{
+    return std::visit(overloaded {
+        [&](const DerivedPath::Built & bfd) -> GoalPtr {
+            return makeDerivationGoal(bfd.drvPath, bfd.outputs, buildMode);
+        },
+        [&](const DerivedPath::Opaque & bo) -> GoalPtr {
+            return makePathSubstitutionGoal(bo.path, buildMode == bmRepair ? Repair : NoRepair);
+        },
+    }, req.raw());
+}
+
+
 template<typename K, typename G>
 static void removeGoal(std::shared_ptr<G> goal, std::map<K, std::weak_ptr<G>> & goalMap)
 {

src/libstore/build/worker.hh

@@ -181,7 +181,7 @@ public:
      */
 
     /**
-     * derivation goal
+     * @ref DerivationGoal "derivation goal"
      */
 private:
     std::shared_ptr<DerivationGoal> makeDerivationGoalCommon(
@@ -196,11 +196,19 @@ public:
         const OutputsSpec & wantedOutputs, BuildMode buildMode = bmNormal);
 
     /**
-     * substitution goal
+     * @ref SubstitutionGoal "substitution goal"
      */
     std::shared_ptr<PathSubstitutionGoal> makePathSubstitutionGoal(const StorePath & storePath, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);
     std::shared_ptr<DrvOutputSubstitutionGoal> makeDrvOutputSubstitutionGoal(const DrvOutput & id, RepairFlag repair = NoRepair, std::optional<ContentAddress> ca = std::nullopt);
 
+    /**
+     * Make a goal corresponding to the `DerivedPath`.
+     *
+     * It will be a `DerivationGoal` for a `DerivedPath::Built` or
+     * a `SubstitutionGoal` for a `DerivedPath::Opaque`.
+     */
+    GoalPtr makeGoal(const DerivedPath & req, BuildMode buildMode = bmNormal);
+
     /**
      * Remove a dead goal.
      */

src/libstore/content-address.cc

@@ -9,7 +9,7 @@ std::string FixedOutputHash::printMethodAlgo() const
     return makeFileIngestionPrefix(method) + printHashType(hash.type);
 }
 
-std::string makeFileIngestionPrefix(const FileIngestionMethod m)
+std::string makeFileIngestionPrefix(FileIngestionMethod m)
 {
     switch (m) {
     case FileIngestionMethod::Flat:
@@ -21,39 +21,35 @@ std::string makeFileIngestionPrefix(const FileIngestionMethod m)
     }
 }
 
-std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash)
+std::string ContentAddress::render() const
-{
-    return "fixed:"
-        + makeFileIngestionPrefix(method)
-        + hash.to_string(Base32, true);
-}
-
-std::string renderContentAddress(ContentAddress ca)
 {
     return std::visit(overloaded {
-        [](TextHash & th) {
+        [](const TextHash & th) {
-            return "text:" + th.hash.to_string(Base32, true);
+            return "text:"
+                + th.hash.to_string(Base32, true);
         },
-        [](FixedOutputHash & fsh) {
+        [](const FixedOutputHash & fsh) {
-            return makeFixedOutputCA(fsh.method, fsh.hash);
+            return "fixed:"
+                + makeFileIngestionPrefix(fsh.method)
+                + fsh.hash.to_string(Base32, true);
         }
-    }, ca);
+    }, raw);
 }
 
-std::string renderContentAddressMethod(ContentAddressMethod cam)
+std::string ContentAddressMethod::render() const
 {
     return std::visit(overloaded {
-        [](TextHashMethod & th) {
+        [](const TextHashMethod & th) {
             return std::string{"text:"} + printHashType(htSHA256);
         },
-        [](FixedOutputHashMethod & fshm) {
+        [](const FixedOutputHashMethod & fshm) {
             return "fixed:" + makeFileIngestionPrefix(fshm.fileIngestionMethod) + printHashType(fshm.hashType);
         }
-    }, cam);
+    }, raw);
 }
 
-/*
+/**
-  Parses content address strings up to the hash.
+ * Parses content address strings up to the hash.
  */
 static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & rest)
 {
@@ -97,7 +93,7 @@ static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & r
         throw UsageError("content address prefix '%s' is unrecognized. Recogonized prefixes are 'text' or 'fixed'", prefix);
 }
 
-ContentAddress parseContentAddress(std::string_view rawCa) {
+ContentAddress ContentAddress::parse(std::string_view rawCa) {
     auto rest = rawCa;
 
     ContentAddressMethod caMethod = parseContentAddressMethodPrefix(rest);
@@ -115,10 +111,10 @@ ContentAddress parseContentAddress(std::string_view rawCa) {
                     .hash = Hash::parseNonSRIUnprefixed(rest, std::move(fohMethod.hashType)),
                 });
             },
-        }, caMethod);
+        }, caMethod.raw);
 }
 
-ContentAddressMethod parseContentAddressMethod(std::string_view caMethod)
+ContentAddressMethod ContentAddressMethod::parse(std::string_view caMethod)
 {
     std::string asPrefix = std::string{caMethod} + ":";
     // parseContentAddressMethodPrefix takes its argument by reference
@@ -126,26 +122,55 @@ ContentAddressMethod parseContentAddressMethod(std::string_view caMethod)
     return parseContentAddressMethodPrefix(asPrefixView);
 }
 
-std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt)
+std::optional<ContentAddress> ContentAddress::parseOpt(std::string_view rawCaOpt)
 {
-    return rawCaOpt == "" ? std::optional<ContentAddress>() : parseContentAddress(rawCaOpt);
+    return rawCaOpt == ""
+        ? std::nullopt
+        : std::optional { ContentAddress::parse(rawCaOpt) };
 };
 
 std::string renderContentAddress(std::optional<ContentAddress> ca)
 {
-    return ca ? renderContentAddress(*ca) : "";
+    return ca ? ca->render() : "";
 }
 
-Hash getContentAddressHash(const ContentAddress & ca)
+const Hash & ContentAddress::getHash() const
 {
     return std::visit(overloaded {
-        [](const TextHash & th) {
+        [](const TextHash & th) -> auto & {
             return th.hash;
         },
-        [](const FixedOutputHash & fsh) {
+        [](const FixedOutputHash & fsh) -> auto & {
             return fsh.hash;
+        },
+    }, raw);
 }
-    }, ca);
+
+bool StoreReferences::empty() const
+{
+    return !self && others.empty();
+}
+
+size_t StoreReferences::size() const
+{
+    return (self ? 1 : 0) + others.size();
+}
+
+ContentAddressWithReferences ContentAddressWithReferences::withoutRefs(const ContentAddress & ca) {
+    return std::visit(overloaded {
+        [&](const TextHash & h) -> ContentAddressWithReferences {
+            return TextInfo {
+                .hash = h,
+                .references = {},
+            };
+        },
+        [&](const FixedOutputHash & h) -> ContentAddressWithReferences {
+            return FixedOutputInfo {
+                .hash = h,
+                .references = {},
+            };
+        },
+    }, ca.raw);
 }
 
 }

src/libstore/content-address.hh

@@ -3,12 +3,30 @@
 
 #include <variant>
 #include "hash.hh"
+#include "path.hh"
 #include "comparator.hh"
 
 namespace nix {
 
+/*
+ * Content addressing method
+ */
+
+/* We only have one way to hash text with references, so this is a single-value
+   type, mainly useful with std::variant.
+*/
+
 /**
- * An enumeration of the ways we can serialize file system objects.
+ * The single way we can serialize "text" file system objects.
+ *
+ * Somewhat obscure, used by \ref Derivation derivations and
+ * `builtins.toFile` currently.
+ */
+struct TextHashMethod : std::monostate { };
+
+/**
+ * An enumeration of the main ways we can serialize file system
+ * objects.
  */
 enum struct FileIngestionMethod : uint8_t {
     /**
@@ -22,6 +40,53 @@ enum struct FileIngestionMethod : uint8_t {
     Recursive = true
 };
 
+/**
+ * Compute the prefix to the hash algorithm which indicates how the
+ * files were ingested.
+ */
+std::string makeFileIngestionPrefix(FileIngestionMethod m);
+
+struct FixedOutputHashMethod {
+    FileIngestionMethod fileIngestionMethod;
+    HashType hashType;
+
+    GENERATE_CMP(FixedOutputHashMethod, me->fileIngestionMethod, me->hashType);
+};
+
+/**
+ * An enumeration of all the ways we can serialize file system objects.
+ *
+ * Just the type of a content address. Combine with the hash itself, and
+ * we have a `ContentAddress` as defined below. Combine that, in turn,
+ * with info on references, and we have `ContentAddressWithReferences`,
+ * as defined further below.
+ */
+struct ContentAddressMethod
+{
+    typedef std::variant<
+        TextHashMethod,
+        FixedOutputHashMethod
+    > Raw;
+
+    Raw raw;
+
+    GENERATE_CMP(ContentAddressMethod, me->raw);
+
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddressMethod(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
+
+    static ContentAddressMethod parse(std::string_view rawCaMethod);
+
+    std::string render() const;
+};
+
+
+/*
+ * Mini content address
+ */
+
 /**
  * Somewhat obscure, used by \ref Derivation derivations and
  * `builtins.toFile` currently.
@@ -36,7 +101,7 @@ struct TextHash {
 };
 
 /**
- * For path computed by makeFixedOutputPath.
+ * Used by most store objects that are content-addressed.
  */
 struct FixedOutputHash {
     /**
@@ -65,41 +130,96 @@ struct FixedOutputHash {
  * - ‘fixed:<r?>:<ht>:<h>’: For paths computed by
  *   Store::makeFixedOutputPath() / Store::addToStore().
  */
+struct ContentAddress
+{
     typedef std::variant<
         TextHash,
         FixedOutputHash
-> ContentAddress;
+    > Raw;
 
-/**
+    Raw raw;
- * Compute the prefix to the hash algorithm which indicates how the
+
- * files were ingested.
+    GENERATE_CMP(ContentAddress, me->raw);
- */
+
-std::string makeFileIngestionPrefix(const FileIngestionMethod m);
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddress(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
 
     /**
      * Compute the content-addressability assertion (ValidPathInfo::ca) for
      * paths created by Store::makeFixedOutputPath() / Store::addToStore().
      */
-std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash);
+    std::string render() const;
 
-std::string renderContentAddress(ContentAddress ca);
+    static ContentAddress parse(std::string_view rawCa);
+
+    static std::optional<ContentAddress> parseOpt(std::string_view rawCaOpt);
+
+    const Hash & getHash() const;
+};
 
 std::string renderContentAddress(std::optional<ContentAddress> ca);
 
-ContentAddress parseContentAddress(std::string_view rawCa);
-
-std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt);
-
-Hash getContentAddressHash(const ContentAddress & ca);
 
 /*
-  We only have one way to hash text with references, so this is single-value
+ * Full content address
-  type is only useful in std::variant.
+ *
+ * See the schema for store paths in store-api.cc
  */
-struct TextHashMethod { };
+
-struct FixedOutputHashMethod {
+/**
-  FileIngestionMethod fileIngestionMethod;
+ * A set of references to other store objects.
-  HashType hashType;
+ *
+ * References to other store objects are tracked with store paths, self
+ * references however are tracked with a boolean.
+ */
+struct StoreReferences {
+    /**
+     * References to other store objects
+     */
+    StorePathSet others;
+
+    /**
+     * Reference to this store object
+     */
+    bool self = false;
+
+    /**
+     * @return true iff no references, i.e. others is empty and self is
+     * false.
+     */
+    bool empty() const;
+
+    /**
+     * Returns the numbers of references, i.e. the size of others + 1
+     * iff self is true.
+     */
+    size_t size() const;
+
+    GENERATE_CMP(StoreReferences, me->self, me->others);
+};
+
+// This matches the additional info that we need for makeTextPath
+struct TextInfo {
+    TextHash hash;
+    /**
+     * References to other store objects only; self references
+     * disallowed
+     */
+    StorePathSet references;
+
+    GENERATE_CMP(TextInfo, me->hash, me->references);
+};
+
+struct FixedOutputInfo {
+    FixedOutputHash hash;
+    /**
+     * References to other store objects or this one.
+     */
+    StoreReferences references;
+
+    GENERATE_CMP(FixedOutputInfo, me->hash, me->references);
 };
 
 /**
@@ -107,13 +227,27 @@ struct FixedOutputHashMethod {
  *
  * A ContentAddress without a Hash.
  */
+struct ContentAddressWithReferences
+{
     typedef std::variant<
-    TextHashMethod,
+        TextInfo,
-    FixedOutputHashMethod
+        FixedOutputInfo
-  > ContentAddressMethod;
+    > Raw;
 
-ContentAddressMethod parseContentAddressMethod(std::string_view rawCaMethod);
+    Raw raw;
 
-std::string renderContentAddressMethod(ContentAddressMethod caMethod);
+    GENERATE_CMP(ContentAddressWithReferences, me->raw);
+
+    /* The moral equivalent of `using Raw::Raw;` */
+    ContentAddressWithReferences(auto &&... arg)
+        : raw(std::forward<decltype(arg)>(arg)...)
+    { }
+
+    /**
+     * Create a ContentAddressWithReferences from a mere ContentAddress, by
+     * assuming no references in all cases.
+     */
+    static ContentAddressWithReferences withoutRefs(const ContentAddress &);
+};
 
 }

src/libstore/daemon.cc

@@ -401,21 +401,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             logger->startWork();
             auto pathInfo = [&]() {
                 // NB: FramedSource must be out of scope before logger->stopWork();
-                ContentAddressMethod contentAddressMethod = parseContentAddressMethod(camStr);
+                ContentAddressMethod contentAddressMethod = ContentAddressMethod::parse(camStr);
                 FramedSource source(from);
                 // TODO this is essentially RemoteStore::addCAToStore. Move it up to Store.
                 return std::visit(overloaded {
-                    [&](TextHashMethod &) {
+                    [&](const TextHashMethod &) {
                         // We could stream this by changing Store
                         std::string contents = source.drain();
                         auto path = store->addTextToStore(name, contents, refs, repair);
                         return store->queryPathInfo(path);
                     },
-                    [&](FixedOutputHashMethod & fohm) {
+                    [&](const FixedOutputHashMethod & fohm) {
                         auto path = store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType, repair, refs);
                         return store->queryPathInfo(path);
                     },
-                }, contentAddressMethod);
+                }, contentAddressMethod.raw);
             }();
             logger->stopWork();
 
@@ -637,7 +637,10 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
             to << res.timesBuilt << res.isNonDeterministic << res.startTime << res.stopTime;
         }
         if (GET_PROTOCOL_MINOR(clientVersion) >= 28) {
-            worker_proto::write(*store, to, res.builtOutputs);
+            DrvOutputs builtOutputs;
+            for (auto & [output, realisation] : res.builtOutputs)
+                builtOutputs.insert_or_assign(realisation.id, realisation);
+            worker_proto::write(*store, to, builtOutputs);
         }
         break;
     }
@@ -880,7 +883,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         info.references = worker_proto::read(*store, from, Phantom<StorePathSet> {});
         from >> info.registrationTime >> info.narSize >> info.ultimate;
         info.sigs = readStrings<StringSet>(from);
-        info.ca = parseContentAddressOpt(readString(from));
+        info.ca = ContentAddress::parseOpt(readString(from));
         from >> repair >> dontCheckSigs;
         if (!trusted && dontCheckSigs)
             dontCheckSigs = false;
@@ -1064,6 +1067,8 @@ void processConnection(
 
             opCount++;
 
+            debug("performing daemon worker op: %d", op);
+
             try {
                 performOp(tunnelLogger, store, trusted, recursive, clientVersion, from, to, op);
             } catch (Error & e) {

src/libstore/derivations.cc

@@ -36,8 +36,8 @@ std::optional<StorePath> DerivationOutput::path(const Store & store, std::string
 StorePath DerivationOutput::CAFixed::path(const Store & store, std::string_view drvName, std::string_view outputName) const
 {
     return store.makeFixedOutputPath(
-        hash.method, hash.hash,
+        outputPathName(drvName, outputName),
-        outputPathName(drvName, outputName));
+        { hash, {} });
 }
 
 
@@ -942,7 +942,7 @@ void Derivation::checkInvariants(Store & store, const StorePath & drvPath) const
                 envHasRightPath(doia.path, i.first);
             },
             [&](const DerivationOutput::CAFixed & dof) {
-                StorePath path = store.makeFixedOutputPath(dof.hash.method, dof.hash.hash, drvName);
+                StorePath path = store.makeFixedOutputPath(drvName, { dof.hash, {} });
                 envHasRightPath(path, i.first);
             },
             [&](const DerivationOutput::CAFloating &) {
@@ -989,7 +989,8 @@ nlohmann::json DerivationOutput::toJSON(
 
 DerivationOutput DerivationOutput::fromJSON(
     const Store & store, std::string_view drvName, std::string_view outputName,
-    const nlohmann::json & _json)
+    const nlohmann::json & _json,
+    const ExperimentalFeatureSettings & xpSettings)
 {
     std::set<std::string_view> keys;
     auto json = (std::map<std::string, nlohmann::json>) _json;
@@ -1028,6 +1029,7 @@ DerivationOutput DerivationOutput::fromJSON(
     }
 
     else if (keys == (std::set<std::string_view> { "hashAlgo" })) {
+        xpSettings.require(Xp::CaDerivations);
         auto [method, hashType] = methodAlgo();
         return DerivationOutput::CAFloating {
             .method = method,
@@ -1040,6 +1042,7 @@ DerivationOutput DerivationOutput::fromJSON(
     }
 
     else if (keys == (std::set<std::string_view> { "hashAlgo", "impure" })) {
+        xpSettings.require(Xp::ImpureDerivations);
         auto [method, hashType] = methodAlgo();
         return DerivationOutput::Impure {
             .method = method,

src/libstore/derivations.hh

@@ -136,11 +136,15 @@ struct DerivationOutput : _DerivationOutputRaw
         const Store & store,
         std::string_view drvName,
         std::string_view outputName) const;
+    /**
+     * @param xpSettings Stop-gap to avoid globals during unit tests.
+     */
     static DerivationOutput fromJSON(
         const Store & store,
         std::string_view drvName,
         std::string_view outputName,
-        const nlohmann::json & json);
+        const nlohmann::json & json,
+        const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
 };
 
 typedef std::map<std::string, DerivationOutput> DerivationOutputs;

src/libstore/globals.cc

@@ -7,12 +7,23 @@
 
 #include <algorithm>
 #include <map>
+#include <mutex>
 #include <thread>
 #include <dlfcn.h>
 #include <sys/utsname.h>
 
 #include <nlohmann/json.hpp>
 
+#include <sodium/core.h>
+
+#ifdef __GLIBC__
+#include <gnu/lib-names.h>
+#include <nss.h>
+#include <dlfcn.h>
+#endif
+
+#include "config-impl.hh"
+
 
 namespace nix {
 
@@ -41,7 +52,6 @@ Settings::Settings()
     , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
     buildUsersGroup = getuid() == 0 ? "nixbld" : "";
-    lockCPU = getEnv("NIX_AFFINITY_HACK") == "1";
     allowSymlinkedStore = getEnv("NIX_IGNORE_SYMLINK_STORE") == "1";
 
     auto sslOverride = getEnv("NIX_SSL_CERT_FILE").value_or(getEnv("SSL_CERT_FILE").value_or(""));
@@ -185,18 +195,18 @@ NLOHMANN_JSON_SERIALIZE_ENUM(SandboxMode, {
     {SandboxMode::smDisabled, false},
 });
 
-template<> void BaseSetting<SandboxMode>::set(const std::string & str, bool append)
+template<> SandboxMode BaseSetting<SandboxMode>::parse(const std::string & str) const
 {
-    if (str == "true") value = smEnabled;
+    if (str == "true") return smEnabled;
-    else if (str == "relaxed") value = smRelaxed;
+    else if (str == "relaxed") return smRelaxed;
-    else if (str == "false") value = smDisabled;
+    else if (str == "false") return smDisabled;
     else throw UsageError("option '%s' has invalid value '%s'", name, str);
 }
 
-template<> bool BaseSetting<SandboxMode>::isAppendable()
+template<> struct BaseSetting<SandboxMode>::trait
 {
-    return false;
+    static constexpr bool appendable = false;
-}
+};
 
 template<> std::string BaseSetting<SandboxMode>::to_string() const
 {
@@ -228,23 +238,23 @@ template<> void BaseSetting<SandboxMode>::convertToArg(Args & args, const std::s
     });
 }
 
-void MaxBuildJobsSetting::set(const std::string & str, bool append)
+unsigned int MaxBuildJobsSetting::parse(const std::string & str) const
 {
-    if (str == "auto") value = std::max(1U, std::thread::hardware_concurrency());
+    if (str == "auto") return std::max(1U, std::thread::hardware_concurrency());
     else {
         if (auto n = string2Int<decltype(value)>(str))
-            value = *n;
+            return *n;
         else
             throw UsageError("configuration setting '%s' should be 'auto' or an integer", name);
     }
 }
 
 
-void PluginFilesSetting::set(const std::string & str, bool append)
+Paths PluginFilesSetting::parse(const std::string & str) const
 {
     if (pluginsLoaded)
         throw UsageError("plugin-files set after plugins were loaded, you may need to move the flag before the subcommand");
-    BaseSetting<Paths>::set(str, append);
+    return BaseSetting<Paths>::parse(str);
 }
 
 
@@ -281,6 +291,42 @@ void initPlugins()
     settings.pluginFiles.pluginsLoaded = true;
 }
 
+static void preloadNSS()
+{
+    /* builtin:fetchurl can trigger a DNS lookup, which with glibc can trigger a dynamic library load of
+       one of the glibc NSS libraries in a sandboxed child, which will fail unless the library's already
+       been loaded in the parent. So we force a lookup of an invalid domain to force the NSS machinery to
+       load its lookup libraries in the parent before any child gets a chance to. */
+    static std::once_flag dns_resolve_flag;
+
+    std::call_once(dns_resolve_flag, []() {
+#ifdef __GLIBC__
+        /* On linux, glibc will run every lookup through the nss layer.
+         * That means every lookup goes, by default, through nscd, which acts as a local
+         * cache.
+         * Because we run builds in a sandbox, we also remove access to nscd otherwise
+         * lookups would leak into the sandbox.
+         *
+         * But now we have a new problem, we need to make sure the nss_dns backend that
+         * does the dns lookups when nscd is not available is loaded or available.
+         *
+         * We can't make it available without leaking nix's environment, so instead we'll
+         * load the backend, and configure nss so it does not try to run dns lookups
+         * through nscd.
+         *
+         * This is technically only used for builtins:fetch* functions so we only care
+         * about dns.
+         *
+         * All other platforms are unaffected.
+         */
+        if (!dlopen(LIBNSS_DNS_SO, RTLD_NOW))
+            warn("unable to load nss_dns backend");
+        // FIXME: get hosts entry from nsswitch.conf.
+        __nss_configure_lookup("hosts", "files dns");
+#endif
+    });
+}
+
 static bool initLibStoreDone = false;
 
 void assertLibStoreInitialized() {
@@ -291,6 +337,24 @@ void assertLibStoreInitialized() {
 }
 
 void initLibStore() {
+
+    initLibUtil();
+
+    if (sodium_init() == -1)
+        throw Error("could not initialise libsodium");
+
+    loadConfFile();
+
+    preloadNSS();
+
+    /* On macOS, don't use the per-session TMPDIR (as set e.g. by
+       sshd). This breaks build users because they don't have access
+       to the TMPDIR, in particular in ‘nix-store --serve’. */
+#if __APPLE__
+    if (hasPrefix(getEnv("TMPDIR").value_or("/tmp"), "/var/folders/"))
+        unsetenv("TMPDIR");
+#endif
+
     initLibStoreDone = true;
 }
 

src/libstore/globals.hh

@@ -26,7 +26,7 @@ struct MaxBuildJobsSetting : public BaseSetting<unsigned int>
         options->addSetting(this);
     }
 
-    void set(const std::string & str, bool append = false) override;
+    unsigned int parse(const std::string & str) const override;
 };
 
 struct PluginFilesSetting : public BaseSetting<Paths>
@@ -43,7 +43,7 @@ struct PluginFilesSetting : public BaseSetting<Paths>
         options->addSetting(this);
     }
 
-    void set(const std::string & str, bool append = false) override;
+    Paths parse(const std::string & str) const override;
 };
 
 const uint32_t maxIdsPerBuild =
@@ -458,11 +458,6 @@ public:
         )",
         {"env-keep-derivations"}};
 
-    /**
-     * Whether to lock the Nix client and worker to the same CPU.
-     */
-    bool lockCPU;
-
     Setting<SandboxMode> sandboxMode{
         this,
         #if __linux__

src/libstore/legacy-ssh-store.cc

@@ -156,7 +156,7 @@ struct LegacySSHStore : public virtual LegacySSHStoreConfig, public virtual Stor
                     throw Error("NAR hash is now mandatory");
                 info->narHash = Hash::parseAnyPrefixed(s);
             }
-            info->ca = parseContentAddressOpt(readString(conn->from));
+            info->ca = ContentAddress::parseOpt(readString(conn->from));
             info->sigs = readStrings<StringSet>(conn->from);
 
             auto s = readString(conn->from);
@@ -287,19 +287,18 @@ public:
 
         conn->to.flush();
 
-        BuildResult status {
+        BuildResult status;
-            .path = DerivedPath::Built {
-                .drvPath = drvPath,
-                .outputs = OutputsSpec::All { },
-            },
-        };
         status.status = (BuildResult::Status) readInt(conn->from);
         conn->from >> status.errorMsg;
 
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 3)
             conn->from >> status.timesBuilt >> status.isNonDeterministic >> status.startTime >> status.stopTime;
         if (GET_PROTOCOL_MINOR(conn->remoteVersion) >= 6) {
-            status.builtOutputs = worker_proto::read(*this, conn->from, Phantom<DrvOutputs> {});
+            auto builtOutputs = worker_proto::read(*this, conn->from, Phantom<DrvOutputs> {});
+            for (auto && [output, realisation] : builtOutputs)
+                status.builtOutputs.insert_or_assign(
+                    std::move(output.outputName),
+                    std::move(realisation));
         }
         return status;
     }
@@ -330,7 +329,7 @@ public:
 
         conn->to.flush();
 
-        BuildResult result { .path = DerivedPath::Opaque { StorePath::dummy } };
+        BuildResult result;
         result.status = (BuildResult::Status) readInt(conn->from);
 
         if (!result.success()) {

src/libstore/local-store.cc

@@ -710,6 +710,7 @@ void canonicalisePathMetaData(const Path & path,
     canonicalisePathMetaData(path, uidRange, inodesSeen);
 }
 
+
 void LocalStore::registerDrvOutput(const Realisation & info, CheckSigsFlag checkSigs)
 {
     experimentalFeatureSettings.require(Xp::CaDerivations);
@@ -888,7 +889,7 @@ std::shared_ptr<const ValidPathInfo> LocalStore::queryPathInfoInternal(State & s
     if (s) info->sigs = tokenizeString<StringSet>(s, " ");
 
     s = (const char *) sqlite3_column_text(state.stmts->QueryPathInfo, 7);
-    if (s) info->ca = parseContentAddressOpt(s);
+    if (s) info->ca = ContentAddress::parseOpt(s);
 
     /* Get the references. */
     auto useQueryReferences(state.stmts->QueryReferences.use()(info->id));
@@ -1221,7 +1222,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
                     printStorePath(info.path), info.narSize, hashResult.second);
 
             if (info.ca) {
-                if (auto foHash = std::get_if<FixedOutputHash>(&*info.ca)) {
+                if (auto foHash = std::get_if<FixedOutputHash>(&info.ca->raw)) {
                     auto actualFoHash = hashCAPath(
                         foHash->method,
                         foHash->hash.type,
@@ -1234,7 +1235,7 @@ void LocalStore::addToStore(const ValidPathInfo & info, Source & source,
                             actualFoHash.hash.to_string(Base32, true));
                     }
                 }
-                if (auto textHash = std::get_if<TextHash>(&*info.ca)) {
+                if (auto textHash = std::get_if<TextHash>(&info.ca->raw)) {
                     auto actualTextHash = hashString(htSHA256, readFile(realPath));
                     if (textHash->hash != actualTextHash) {
                         throw Error("ca hash mismatch importing path '%s';\n  specified: %s\n  got:       %s",
@@ -1320,7 +1321,19 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
 
     auto [hash, size] = hashSink->finish();
 
-    auto dstPath = makeFixedOutputPath(method, hash, name, references);
+    ContentAddressWithReferences desc = FixedOutputInfo {
+        .hash = {
+            .method = method,
+            .hash = hash,
+        },
+        .references = {
+            .others = references,
+            // caller is not capable of creating a self-reference, because this is content-addressed without modulus
+            .self = false,
+        },
+    };
+
+    auto dstPath = makeFixedOutputPathFromCA(name, desc);
 
     addTempRoot(dstPath);
 
@@ -1364,10 +1377,13 @@ StorePath LocalStore::addToStoreFromDump(Source & source0, std::string_view name
 
             optimisePath(realPath, repair);
 
-            ValidPathInfo info { dstPath, narHash.first };
+            ValidPathInfo info {
+                *this,
+                name,
+                std::move(desc),
+                narHash.first
+            };
             info.narSize = narHash.second;
-            info.references = references;
-            info.ca = FixedOutputHash { .method = method, .hash = hash };
             registerValidPath(info);
         }
 
@@ -1384,7 +1400,10 @@ StorePath LocalStore::addTextToStore(
     const StorePathSet & references, RepairFlag repair)
 {
     auto hash = hashString(htSHA256, s);
-    auto dstPath = makeTextPath(name, hash, references);
+    auto dstPath = makeTextPath(name, TextInfo {
+        { .hash = hash },
+        references,
+    });
 
     addTempRoot(dstPath);
 

src/libstore/make-content-addressed.cc

@@ -27,18 +27,17 @@ std::map<StorePath, StorePath> makeContentAddressed(
 
         StringMap rewrites;
 
-        StorePathSet references;
+        StoreReferences refs;
-        bool hasSelfReference = false;
         for (auto & ref : oldInfo->references) {
             if (ref == path)
-                hasSelfReference = true;
+                refs.self = true;
             else {
                 auto i = remappings.find(ref);
                 auto replacement = i != remappings.end() ? i->second : ref;
                 // FIXME: warn about unremapped paths?
                 if (replacement != ref)
                     rewrites.insert_or_assign(srcStore.printStorePath(ref), srcStore.printStorePath(replacement));
-                references.insert(std::move(replacement));
+                refs.others.insert(std::move(replacement));
             }
         }
 
@@ -49,24 +48,28 @@ std::map<StorePath, StorePath> makeContentAddressed(
 
         auto narModuloHash = hashModuloSink.finish().first;
 
-        auto dstPath = dstStore.makeFixedOutputPath(
+        ValidPathInfo info {
-            FileIngestionMethod::Recursive, narModuloHash, path.name(), references, hasSelfReference);
+            dstStore,
+            path.name(),
+            FixedOutputInfo {
+                .hash = {
+                    .method = FileIngestionMethod::Recursive,
+                    .hash = narModuloHash,
+                },
+                .references = std::move(refs),
+            },
+            Hash::dummy,
+        };
 
-        printInfo("rewriting '%s' to '%s'", pathS, srcStore.printStorePath(dstPath));
+        printInfo("rewriting '%s' to '%s'", pathS, dstStore.printStorePath(info.path));
 
         StringSink sink2;
-        RewritingSink rsink2(oldHashPart, std::string(dstPath.hashPart()), sink2);
+        RewritingSink rsink2(oldHashPart, std::string(info.path.hashPart()), sink2);
         rsink2(sink.s);
         rsink2.flush();
 
-        ValidPathInfo info { dstPath, hashString(htSHA256, sink2.s) };
+        info.narHash = hashString(htSHA256, sink2.s);
-        info.references = std::move(references);
-        if (hasSelfReference) info.references.insert(info.path);
         info.narSize = sink.s.size();
-        info.ca = FixedOutputHash {
-            .method = FileIngestionMethod::Recursive,
-            .hash = narModuloHash,
-        };
 
         StringSource source(sink2.s);
         dstStore.addToStore(info, source);

src/libstore/nar-info-disk-cache.cc

@@ -273,7 +273,7 @@ public:
                 narInfo->deriver = StorePath(queryNAR.getStr(9));
             for (auto & sig : tokenizeString<Strings>(queryNAR.getStr(10), " "))
                 narInfo->sigs.insert(sig);
-            narInfo->ca = parseContentAddressOpt(queryNAR.getStr(11));
+            narInfo->ca = ContentAddress::parseOpt(queryNAR.getStr(11));
 
             return {oValid, narInfo};
         });

src/libstore/nar-info.cc

@@ -7,15 +7,18 @@ namespace nix {
 NarInfo::NarInfo(const Store & store, const std::string & s, const std::string & whence)
     : ValidPathInfo(StorePath(StorePath::dummy), Hash(Hash::dummy)) // FIXME: hack
 {
-    auto corrupt = [&]() {
+    unsigned line = 1;
-        return Error("NAR info file '%1%' is corrupt", whence);
+
+    auto corrupt = [&](const char * reason) {
+        return Error("NAR info file '%1%' is corrupt: %2%", whence,
+            std::string(reason) + (line > 0 ? " at line " + std::to_string(line) : ""));
     };
 
     auto parseHashField = [&](const std::string & s) {
         try {
             return Hash::parseAnyPrefixed(s);
         } catch (BadHash &) {
-            throw corrupt();
+            throw corrupt("bad hash");
         }
     };
 
@@ -26,12 +29,12 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
     while (pos < s.size()) {
 
         size_t colon = s.find(':', pos);
-        if (colon == std::string::npos) throw corrupt();
+        if (colon == std::string::npos) throw corrupt("expecting ':'");
 
         std::string name(s, pos, colon - pos);
 
         size_t eol = s.find('\n', colon + 2);
-        if (eol == std::string::npos) throw corrupt();
+        if (eol == std::string::npos) throw corrupt("expecting '\\n'");
 
         std::string value(s, colon + 2, eol - colon - 2);
 
@@ -47,7 +50,7 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
             fileHash = parseHashField(value);
         else if (name == "FileSize") {
             auto n = string2Int<decltype(fileSize)>(value);
-            if (!n) throw corrupt();
+            if (!n) throw corrupt("invalid FileSize");
             fileSize = *n;
         }
         else if (name == "NarHash") {
@@ -56,12 +59,12 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         }
         else if (name == "NarSize") {
             auto n = string2Int<decltype(narSize)>(value);
-            if (!n) throw corrupt();
+            if (!n) throw corrupt("invalid NarSize");
             narSize = *n;
         }
         else if (name == "References") {
             auto refs = tokenizeString<Strings>(value, " ");
-            if (!references.empty()) throw corrupt();
+            if (!references.empty()) throw corrupt("extra References");
             for (auto & r : refs)
                 references.insert(StorePath(r));
         }
@@ -72,17 +75,26 @@ NarInfo::NarInfo(const Store & store, const std::string & s, const std::string &
         else if (name == "Sig")
             sigs.insert(value);
         else if (name == "CA") {
-            if (ca) throw corrupt();
+            if (ca) throw corrupt("extra CA");
             // FIXME: allow blank ca or require skipping field?
-            ca = parseContentAddressOpt(value);
+            ca = ContentAddress::parseOpt(value);
         }
 
         pos = eol + 1;
+        line += 1;
     }
 
     if (compression == "") compression = "bzip2";
 
-    if (!havePath || !haveNarHash || url.empty() || narSize == 0) throw corrupt();
+    if (!havePath || !haveNarHash || url.empty() || narSize == 0) {
+        line = 0; // don't include line information in the error
+        throw corrupt(
+            !havePath ? "StorePath missing" :
+            !haveNarHash ? "NarHash missing" :
+            url.empty() ? "URL missing" :
+            narSize == 0 ? "NarSize missing or zero"
+            : "?");
+    }
 }
 
 std::string NarInfo::to_string(const Store & store) const

src/libstore/nar-info.hh

@@ -17,6 +17,9 @@ struct NarInfo : ValidPathInfo
     uint64_t fileSize = 0;
 
     NarInfo() = delete;
+    NarInfo(const Store & store, std::string && name, ContentAddressWithReferences && ca, Hash narHash)
+        : ValidPathInfo(store, std::move(name), std::move(ca), narHash)
+    { }
     NarInfo(StorePath && path, Hash narHash) : ValidPathInfo(std::move(path), narHash) { }
     NarInfo(const ValidPathInfo & info) : ValidPathInfo(info) { }
     NarInfo(const Store & store, const std::string & s, const std::string & whence);

src/libstore/path-info.cc

@@ -21,25 +21,45 @@ void ValidPathInfo::sign(const Store & store, const SecretKey & secretKey)
     sigs.insert(secretKey.signDetached(fingerprint(store)));
 }
 
-
+std::optional<ContentAddressWithReferences> ValidPathInfo::contentAddressWithReferences() const
-bool ValidPathInfo::isContentAddressed(const Store & store) const
 {
-    if (! ca) return false;
+    if (! ca)
+        return std::nullopt;
 
-    auto caPath = std::visit(overloaded {
+    return std::visit(overloaded {
-        [&](const TextHash & th) {
+        [&](const TextHash & th) -> ContentAddressWithReferences {
-            return store.makeTextPath(path.name(), th.hash, references);
+            assert(references.count(path) == 0);
+            return TextInfo {
+                .hash = th,
+                .references = references,
+            };
         },
-        [&](const FixedOutputHash & fsh) {
+        [&](const FixedOutputHash & foh) -> ContentAddressWithReferences {
             auto refs = references;
             bool hasSelfReference = false;
             if (refs.count(path)) {
                 hasSelfReference = true;
                 refs.erase(path);
             }
-            return store.makeFixedOutputPath(fsh.method, fsh.hash, path.name(), refs, hasSelfReference);
+            return FixedOutputInfo {
+                .hash = foh,
+                .references = {
+                    .others = std::move(refs),
+                    .self = hasSelfReference,
+                },
+            };
+        },
+    }, ca->raw);
 }
-    }, *ca);
+
+bool ValidPathInfo::isContentAddressed(const Store & store) const
+{
+    auto fullCaOpt = contentAddressWithReferences();
+
+    if (! fullCaOpt)
+        return false;
+
+    auto caPath = store.makeFixedOutputPathFromCA(path.name(), *fullCaOpt);
 
     bool res = caPath == path;
 
@@ -77,6 +97,29 @@ Strings ValidPathInfo::shortRefs() const
 }
 
 
+ValidPathInfo::ValidPathInfo(
+    const Store & store,
+    std::string_view name,
+    ContentAddressWithReferences && ca,
+    Hash narHash)
+      : path(store.makeFixedOutputPathFromCA(name, ca))
+      , narHash(narHash)
+{
+    std::visit(overloaded {
+        [this](TextInfo && ti) {
+            this->references = std::move(ti.references);
+            this->ca = std::move((TextHash &&) ti);
+        },
+        [this](FixedOutputInfo && foi) {
+            this->references = std::move(foi.references.others);
+            if (foi.references.self)
+                this->references.insert(path);
+            this->ca = std::move((FixedOutputHash &&) foi);
+        },
+    }, std::move(ca).raw);
+}
+
+
 ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned int format)
 {
     return read(source, store, format, store.parseStorePath(readString(source)));
@@ -93,7 +136,7 @@ ValidPathInfo ValidPathInfo::read(Source & source, const Store & store, unsigned
     if (format >= 16) {
         source >> info.ultimate;
         info.sigs = readStrings<StringSet>(source);
-        info.ca = parseContentAddressOpt(readString(source));
+        info.ca = ContentAddress::parseOpt(readString(source));
     }
     return info;
 }

src/libstore/path-info.hh

@@ -92,6 +92,13 @@ struct ValidPathInfo
 
     void sign(const Store & store, const SecretKey & secretKey);
 
+	/**
+	 * @return The `ContentAddressWithReferences` that determines the
+	 * store path for a content-addressed store object, `std::nullopt`
+	 * for an input-addressed store object.
+	 */
+    std::optional<ContentAddressWithReferences> contentAddressWithReferences() const;
+
     /**
      * @return true iff the path is verifiably content-addressed.
      */
@@ -118,6 +125,9 @@ struct ValidPathInfo
     ValidPathInfo(StorePath && path, Hash narHash) : path(std::move(path)), narHash(narHash) { };
     ValidPathInfo(const StorePath & path, Hash narHash) : path(path), narHash(narHash) { };
 
+    ValidPathInfo(const Store & store,
+        std::string_view name, ContentAddressWithReferences && ca, Hash narHash);
+
     virtual ~ValidPathInfo() { }
 
     static ValidPathInfo read(Source & source, const Store & store, unsigned int format);

src/libstore/realisation.hh

@@ -13,9 +13,25 @@ namespace nix {
 
 class Store;
 
+/**
+ * A general `Realisation` key.
+ *
+ * This is similar to a `DerivedPath::Opaque`, but the derivation is
+ * identified by its "hash modulo" instead of by its store path.
+ */
 struct DrvOutput {
-    // The hash modulo of the derivation
+    /**
+     * The hash modulo of the derivation.
+     *
+     * Computed from the derivation itself for most types of
+     * derivations, but computed from the (fixed) content address of the
+     * output for fixed-output derivations.
+     */
     Hash drvHash;
+
+    /**
+     * The name of the output.
+     */
     std::string outputName;
 
     std::string to_string() const;
@@ -60,6 +76,21 @@ struct Realisation {
     GENERATE_CMP(Realisation, me->id, me->outPath);
 };
 
+/**
+ * Collection type for a single derivation's outputs' `Realisation`s.
+ *
+ * Since these are the outputs of a single derivation, we know the
+ * output names are unique so we can use them as the map key.
+ */
+typedef std::map<std::string, Realisation> SingleDrvOutputs;
+
+/**
+ * Collection type for multiple derivations' outputs' `Realisation`s.
+ *
+ * `DrvOutput` is used because in general the derivations are not all
+ * the same, so we need to identify firstly which derivation, and
+ * secondly which output of that derivation.
+ */
 typedef std::map<DrvOutput, Realisation> DrvOutputs;
 
 struct OpaquePath {

src/libstore/remote-store.cc

@@ -78,7 +78,7 @@ void write(const Store & store, Sink & out, const std::optional<TrustedFlag> & o
 
 ContentAddress read(const Store & store, Source & from, Phantom<ContentAddress> _)
 {
-    return parseContentAddress(readString(from));
+    return ContentAddress::parse(readString(from));
 }
 
 void write(const Store & store, Sink & out, const ContentAddress & ca)
@@ -125,10 +125,26 @@ void write(const Store & store, Sink & out, const DrvOutput & drvOutput)
 }
 
 
-BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
+KeyedBuildResult read(const Store & store, Source & from, Phantom<KeyedBuildResult> _)
 {
     auto path = worker_proto::read(store, from, Phantom<DerivedPath> {});
-    BuildResult res { .path = path };
+    auto br = worker_proto::read(store, from, Phantom<BuildResult> {});
+    return KeyedBuildResult {
+        std::move(br),
+        /* .path = */ std::move(path),
+    };
+}
+
+void write(const Store & store, Sink & to, const KeyedBuildResult & res)
+{
+    worker_proto::write(store, to, res.path);
+    worker_proto::write(store, to, static_cast<const BuildResult &>(res));
+}
+
+
+BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
+{
+    BuildResult res;
     res.status = (BuildResult::Status) readInt(from);
     from
         >> res.errorMsg
@@ -136,13 +152,16 @@ BuildResult read(const Store & store, Source & from, Phantom<BuildResult> _)
         >> res.isNonDeterministic
         >> res.startTime
         >> res.stopTime;
-    res.builtOutputs = worker_proto::read(store, from, Phantom<DrvOutputs> {});
+    auto builtOutputs = worker_proto::read(store, from, Phantom<DrvOutputs> {});
+    for (auto && [output, realisation] : builtOutputs)
+        res.builtOutputs.insert_or_assign(
+            std::move(output.outputName),
+            std::move(realisation));
     return res;
 }
 
 void write(const Store & store, Sink & to, const BuildResult & res)
 {
-    worker_proto::write(store, to, res.path);
     to
         << res.status
         << res.errorMsg
@@ -150,7 +169,10 @@ void write(const Store & store, Sink & to, const BuildResult & res)
         << res.isNonDeterministic
         << res.startTime
         << res.stopTime;
-    worker_proto::write(store, to, res.builtOutputs);
+    DrvOutputs builtOutputs;
+    for (auto & [output, realisation] : res.builtOutputs)
+        builtOutputs.insert_or_assign(realisation.id, realisation);
+    worker_proto::write(store, to, builtOutputs);
 }
 
 
@@ -168,7 +190,7 @@ void write(const Store & store, Sink & out, const std::optional<StorePath> & sto
 
 std::optional<ContentAddress> read(const Store & store, Source & from, Phantom<std::optional<ContentAddress>> _)
 {
-    return parseContentAddressOpt(readString(from));
+    return ContentAddress::parseOpt(readString(from));
 }
 
 void write(const Store & store, Sink & out, const std::optional<ContentAddress> & caOpt)
@@ -586,7 +608,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
         conn->to
             << wopAddToStore
             << name
-            << renderContentAddressMethod(caMethod);
+            << caMethod.render();
         worker_proto::write(*this, conn->to, references);
         conn->to << repair;
 
@@ -644,7 +666,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
                 }
 
             }
-        }, caMethod);
+        }, caMethod.raw);
         auto path = parseStorePath(readString(conn->from));
         // Release our connection to prevent a deadlock in queryPathInfo().
         conn_.reset();
@@ -865,7 +887,7 @@ void RemoteStore::buildPaths(const std::vector<DerivedPath> & drvPaths, BuildMod
     readInt(conn->from);
 }
 
-std::vector<BuildResult> RemoteStore::buildPathsWithResults(
+std::vector<KeyedBuildResult> RemoteStore::buildPathsWithResults(
     const std::vector<DerivedPath> & paths,
     BuildMode buildMode,
     std::shared_ptr<Store> evalStore)
@@ -880,7 +902,7 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
         writeDerivedPaths(*this, conn, paths);
         conn->to << buildMode;
         conn.processStderr();
-        return worker_proto::read(*this, conn->from, Phantom<std::vector<BuildResult>> {});
+        return worker_proto::read(*this, conn->from, Phantom<std::vector<KeyedBuildResult>> {});
     } else {
         // Avoid deadlock.
         conn_.reset();
@@ -889,21 +911,25 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
         // fails, but meh.
         buildPaths(paths, buildMode, evalStore);
 
-        std::vector<BuildResult> results;
+        std::vector<KeyedBuildResult> results;
 
         for (auto & path : paths) {
             std::visit(
                 overloaded {
                     [&](const DerivedPath::Opaque & bo) {
-                        results.push_back(BuildResult {
+                        results.push_back(KeyedBuildResult {
+                            {
                                 .status = BuildResult::Substituted,
-                            .path = bo,
+                            },
+                            /* .path = */ bo,
                         });
                     },
                     [&](const DerivedPath::Built & bfd) {
-                        BuildResult res {
+                        KeyedBuildResult res {
-                            .status = BuildResult::Built,
+                            {
-                            .path = bfd,
+                                .status = BuildResult::Built
+                            },
+                            /* .path = */ bfd,
                         };
 
                         OutputPathMap outputs;
@@ -922,10 +948,10 @@ std::vector<BuildResult> RemoteStore::buildPathsWithResults(
                                     queryRealisation(outputId);
                                 if (!realisation)
                                     throw MissingRealisation(outputId);
-                                res.builtOutputs.emplace(realisation->id, *realisation);
+                                res.builtOutputs.emplace(output, *realisation);
                             } else {
                                 res.builtOutputs.emplace(
-                                    outputId,
+                                    output,
                                     Realisation {
                                         .id = outputId,
                                         .outPath = outputPath,
@@ -952,12 +978,7 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
     writeDerivation(conn->to, *this, drv);
     conn->to << buildMode;
     conn.processStderr();
-    BuildResult res {
+    BuildResult res;
-        .path = DerivedPath::Built {
-            .drvPath = drvPath,
-            .outputs = OutputsSpec::All { },
-        },
-    };
     res.status = (BuildResult::Status) readInt(conn->from);
     conn->from >> res.errorMsg;
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 29) {
@@ -965,7 +986,10 @@ BuildResult RemoteStore::buildDerivation(const StorePath & drvPath, const BasicD
     }
     if (GET_PROTOCOL_MINOR(conn->daemonVersion) >= 28) {
         auto builtOutputs = worker_proto::read(*this, conn->from, Phantom<DrvOutputs> {});
-        res.builtOutputs = builtOutputs;
+        for (auto && [output, realisation] : builtOutputs)
+            res.builtOutputs.insert_or_assign(
+                std::move(output.outputName),
+                std::move(realisation));
     }
     return res;
 }

src/libstore/remote-store.hh

@@ -114,7 +114,7 @@ public:
 
     void buildPaths(const std::vector<DerivedPath> & paths, BuildMode buildMode, std::shared_ptr<Store> evalStore) override;
 
-    std::vector<BuildResult> buildPathsWithResults(
+    std::vector<KeyedBuildResult> buildPathsWithResults(
         const std::vector<DerivedPath> & paths,
         BuildMode buildMode,
         std::shared_ptr<Store> evalStore) override;

src/libstore/store-api.cc

@@ -7,6 +7,7 @@
 #include "nar-info-disk-cache.hh"
 #include "thread-pool.hh"
 #include "url.hh"
+#include "references.hh"
 #include "archive.hh"
 #include "callback.hh"
 #include "remote-store.hh"
@@ -98,10 +99,12 @@ StorePath Store::followLinksToStorePath(std::string_view path) const
        silly, but it's done that way for compatibility).  <id> is the
        name of the output (usually, "out").
 
-   <h2> = base-16 representation of a SHA-256 hash of:
+   <h2> = base-16 representation of a SHA-256 hash of <s2>
+
+   <s2> =
      if <type> = "text:...":
        the string written to the resulting store path
-     if <type> = "source":
+     if <type> = "source:...":
        the serialisation of the path from which this store path is
        copied, as returned by hashPath()
      if <type> = "output:<id>":
@@ -162,63 +165,63 @@ StorePath Store::makeOutputPath(std::string_view id,
 }
 
 
+/* Stuff the references (if any) into the type.  This is a bit
+   hacky, but we can't put them in, say, <s2> (per the grammar above)
+   since that would be ambiguous. */
 static std::string makeType(
     const Store & store,
     std::string && type,
-    const StorePathSet & references,
+    const StoreReferences & references)
-    bool hasSelfReference = false)
 {
-    for (auto & i : references) {
+    for (auto & i : references.others) {
         type += ":";
         type += store.printStorePath(i);
     }
-    if (hasSelfReference) type += ":self";
+    if (references.self) type += ":self";
     return std::move(type);
 }
 
 
-StorePath Store::makeFixedOutputPath(
+StorePath Store::makeFixedOutputPath(std::string_view name, const FixedOutputInfo & info) const
-    FileIngestionMethod method,
-    const Hash & hash,
-    std::string_view name,
-    const StorePathSet & references,
-    bool hasSelfReference) const
 {
-    if (hash.type == htSHA256 && method == FileIngestionMethod::Recursive) {
+    if (info.hash.hash.type == htSHA256 && info.hash.method == FileIngestionMethod::Recursive) {
-        return makeStorePath(makeType(*this, "source", references, hasSelfReference), hash, name);
+        return makeStorePath(makeType(*this, "source", info.references), info.hash.hash, name);
     } else {
-        assert(references.empty());
+        assert(info.references.size() == 0);
         return makeStorePath("output:out",
             hashString(htSHA256,
                 "fixed:out:"
-                + makeFileIngestionPrefix(method)
+                + makeFileIngestionPrefix(info.hash.method)
-                + hash.to_string(Base16, true) + ":"),
+                + info.hash.hash.to_string(Base16, true) + ":"),
             name);
     }
 }
 
-StorePath Store::makeFixedOutputPathFromCA(std::string_view name, ContentAddress ca,
+
-    const StorePathSet & references, bool hasSelfReference) const
+StorePath Store::makeTextPath(std::string_view name, const TextInfo & info) const
+{
+    assert(info.hash.hash.type == htSHA256);
+    return makeStorePath(
+        makeType(*this, "text", StoreReferences {
+            .others = info.references,
+            .self = false,
+        }),
+        info.hash.hash,
+        name);
+}
+
+
+StorePath Store::makeFixedOutputPathFromCA(std::string_view name, const ContentAddressWithReferences & ca) const
 {
     // New template
     return std::visit(overloaded {
-        [&](const TextHash & th) {
+        [&](const TextInfo & ti) {
-            return makeTextPath(name, th.hash, references);
+            return makeTextPath(name, ti);
         },
-        [&](const FixedOutputHash & fsh) {
+        [&](const FixedOutputInfo & foi) {
-            return makeFixedOutputPath(fsh.method, fsh.hash, name, references, hasSelfReference);
+            return makeFixedOutputPath(name, foi);
         }
-    }, ca);
+    }, ca.raw);
-}
-
-StorePath Store::makeTextPath(std::string_view name, const Hash & hash,
-    const StorePathSet & references) const
-{
-    assert(hash.type == htSHA256);
-    /* Stuff the references (if any) into the type.  This is a bit
-       hacky, but we can't put them in `s' since that would be
-       ambiguous. */
-    return makeStorePath(makeType(*this, "text", references), hash, name);
 }
 
 
@@ -228,7 +231,14 @@ std::pair<StorePath, Hash> Store::computeStorePathForPath(std::string_view name,
     Hash h = method == FileIngestionMethod::Recursive
         ? hashPath(hashAlgo, srcPath, filter).first
         : hashFile(hashAlgo, srcPath);
-    return std::make_pair(makeFixedOutputPath(method, h, name), h);
+    FixedOutputInfo caInfo {
+        .hash = {
+            .method = method,
+            .hash = h,
+        },
+        .references = {},
+    };
+    return std::make_pair(makeFixedOutputPath(name, caInfo), h);
 }
 
 
@@ -237,7 +247,10 @@ StorePath Store::computeStorePathForText(
     std::string_view s,
     const StorePathSet & references) const
 {
-    return makeTextPath(name, hashString(htSHA256, s), references);
+    return makeTextPath(name, TextInfo {
+        { .hash = hashString(htSHA256, s) },
+        references,
+    });
 }
 
 
@@ -425,11 +438,18 @@ ValidPathInfo Store::addToStoreSlow(std::string_view name, const Path & srcPath,
         throw Error("hash mismatch for '%s'", srcPath);
 
     ValidPathInfo info {
-        makeFixedOutputPath(method, hash, name),
+        *this,
+        name,
+        FixedOutputInfo {
+            .hash = {
+                .method = method,
+                .hash = hash,
+            },
+            .references = {},
+        },
         narHash,
     };
     info.narSize = narSize;
-    info.ca = FixedOutputHash { .method = method, .hash = hash };
 
     if (!isValidPath(info.path)) {
         auto source = sinkToSource([&](Sink & scratchpadSink) {
@@ -521,7 +541,9 @@ void Store::querySubstitutablePathInfos(const StorePathCAMap & paths, Substituta
 
             // Recompute store path so that we can use a different store root.
             if (path.second) {
-                subPath = makeFixedOutputPathFromCA(path.first.name(), *path.second);
+                subPath = makeFixedOutputPathFromCA(
+                    path.first.name(),
+                    ContentAddressWithReferences::withoutRefs(*path.second));
                 if (sub->storeDir == storeDir)
                     assert(subPath == path.first);
                 if (subPath != path.first)
@@ -538,10 +560,11 @@ void Store::querySubstitutablePathInfos(const StorePathCAMap & paths, Substituta
                 auto narInfo = std::dynamic_pointer_cast<const NarInfo>(
                     std::shared_ptr<const ValidPathInfo>(info));
                 infos.insert_or_assign(path.first, SubstitutablePathInfo{
-                    info->deriver,
+                    .deriver = info->deriver,
-                    info->references,
+                    .references = info->references,
-                    narInfo ? narInfo->fileSize : 0,
+                    .downloadSize = narInfo ? narInfo->fileSize : 0,
-                    info->narSize});
+                    .narSize = info->narSize,
+                });
             } catch (InvalidPath &) {
             } catch (SubstituterDisabled &) {
             } catch (Error & e) {
@@ -1025,7 +1048,9 @@ void copyStorePath(
     // recompute store path on the chance dstStore does it differently
     if (info->ca && info->references.empty()) {
         auto info2 = make_ref<ValidPathInfo>(*info);
-        info2->path = dstStore.makeFixedOutputPathFromCA(info->path.name(), *info->ca);
+        info2->path = dstStore.makeFixedOutputPathFromCA(
+            info->path.name(),
+            info->contentAddressWithReferences().value());
         if (dstStore.storeDir == srcStore.storeDir)
             assert(info->path == info2->path);
         info = info2;
@@ -1137,7 +1162,9 @@ std::map<StorePath, StorePath> copyPaths(
         auto storePathForSrc = currentPathInfo.path;
         auto storePathForDst = storePathForSrc;
         if (currentPathInfo.ca && currentPathInfo.references.empty()) {
-            storePathForDst = dstStore.makeFixedOutputPathFromCA(storePathForSrc.name(), *currentPathInfo.ca);
+            storePathForDst = dstStore.makeFixedOutputPathFromCA(
+                currentPathInfo.path.name(),
+                currentPathInfo.contentAddressWithReferences().value());
             if (dstStore.storeDir == srcStore.storeDir)
                 assert(storePathForDst == storePathForSrc);
             if (storePathForDst != storePathForSrc)

src/libstore/store-api.hh

@@ -92,6 +92,7 @@ enum BuildMode { bmNormal, bmRepair, bmCheck };
 enum TrustedFlag : bool { NotTrusted = false, Trusted = true };
 
 struct BuildResult;
+struct KeyedBuildResult;
 
 
 typedef std::map<StorePath, std::optional<ContentAddress>> StorePathCAMap;
@@ -268,17 +269,11 @@ public:
     StorePath makeOutputPath(std::string_view id,
         const Hash & hash, std::string_view name) const;
 
-    StorePath makeFixedOutputPath(FileIngestionMethod method,
+    StorePath makeFixedOutputPath(std::string_view name, const FixedOutputInfo & info) const;
-        const Hash & hash, std::string_view name,
-        const StorePathSet & references = {},
-        bool hasSelfReference = false) const;
 
-    StorePath makeTextPath(std::string_view name, const Hash & hash,
+    StorePath makeTextPath(std::string_view name, const TextInfo & info) const;
-        const StorePathSet & references = {}) const;
 
-    StorePath makeFixedOutputPathFromCA(std::string_view name, ContentAddress ca,
+    StorePath makeFixedOutputPathFromCA(std::string_view name, const ContentAddressWithReferences & ca) const;
-        const StorePathSet & references = {},
-        bool hasSelfReference = false) const;
 
     /**
      * Preparatory part of addToStore().
@@ -575,7 +570,7 @@ public:
      * case of a build/substitution error, this function won't throw an
      * exception, but return a BuildResult containing an error message.
      */
-    virtual std::vector<BuildResult> buildPathsWithResults(
+    virtual std::vector<KeyedBuildResult> buildPathsWithResults(
         const std::vector<DerivedPath> & paths,
         BuildMode buildMode = bmNormal,
         std::shared_ptr<Store> evalStore = nullptr);

src/libstore/tests/derivation.cc

@@ -1,6 +1,7 @@
 #include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
 
+#include "experimental-features.hh"
 #include "derivations.hh"
 
 #include "tests/libstore.hh"
@@ -9,10 +10,32 @@ namespace nix {
 
 class DerivationTest : public LibStoreTest
 {
+public:
+    /**
+     * We set these in tests rather than the regular globals so we don't have
+     * to worry about race conditions if the tests run concurrently.
+     */
+    ExperimentalFeatureSettings mockXpSettings;
 };
 
-#define TEST_JSON(NAME, STR, VAL, DRV_NAME, OUTPUT_NAME) \
+class CaDerivationTest : public DerivationTest
-    TEST_F(DerivationTest, DerivationOutput_ ## NAME ## _to_json) {    \
+{
+    void SetUp() override
+    {
+        mockXpSettings.set("experimental-features", "ca-derivations");
+    }
+};
+
+class ImpureDerivationTest : public DerivationTest
+{
+    void SetUp() override
+    {
+        mockXpSettings.set("experimental-features", "impure-derivations");
+    }
+};
+
+#define TEST_JSON(FIXTURE, NAME, STR, VAL, DRV_NAME, OUTPUT_NAME) \
+    TEST_F(FIXTURE, DerivationOutput_ ## NAME ## _to_json) {    \
         using nlohmann::literals::operator "" _json;           \
         ASSERT_EQ(                                             \
             STR ## _json,                                      \
@@ -22,7 +45,7 @@ class DerivationTest : public LibStoreTest
                 OUTPUT_NAME));                                 \
     }                                                          \
                                                                \
-    TEST_F(DerivationTest, DerivationOutput_ ## NAME ## _from_json) {  \
+    TEST_F(FIXTURE, DerivationOutput_ ## NAME ## _from_json) {  \
         using nlohmann::literals::operator "" _json;           \
         ASSERT_EQ(                                             \
             DerivationOutput { VAL },                          \
@@ -30,10 +53,11 @@ class DerivationTest : public LibStoreTest
                 *store,                                        \
                 DRV_NAME,                                      \
                 OUTPUT_NAME,                                   \
-                STR ## _json));                                \
+                STR ## _json,                                  \
+                mockXpSettings));                              \
     }
 
-TEST_JSON(inputAddressed,
+TEST_JSON(DerivationTest, inputAddressed,
     R"({
         "path": "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-drv-name-output-name"
     })",
@@ -42,7 +66,7 @@ TEST_JSON(inputAddressed,
     }),
     "drv-name", "output-name")
 
-TEST_JSON(caFixed,
+TEST_JSON(DerivationTest, caFixed,
     R"({
         "hashAlgo": "r:sha256",
         "hash": "894517c9163c896ec31a2adbd33c0681fd5f45b2c0ef08a64c92a03fb97f390f",
@@ -56,7 +80,7 @@ TEST_JSON(caFixed,
     }),
     "drv-name", "output-name")
 
-TEST_JSON(caFloating,
+TEST_JSON(CaDerivationTest, caFloating,
     R"({
         "hashAlgo": "r:sha256"
     })",
@@ -66,12 +90,12 @@ TEST_JSON(caFloating,
     }),
     "drv-name", "output-name")
 
-TEST_JSON(deferred,
+TEST_JSON(DerivationTest, deferred,
     R"({ })",
     DerivationOutput::Deferred { },
     "drv-name", "output-name")
 
-TEST_JSON(impure,
+TEST_JSON(ImpureDerivationTest, impure,
     R"({
         "hashAlgo": "r:sha256",
         "impure": true

src/libstore/worker-protocol.hh

@@ -103,6 +103,7 @@ MAKE_WORKER_PROTO(, DerivedPath);
 MAKE_WORKER_PROTO(, Realisation);
 MAKE_WORKER_PROTO(, DrvOutput);
 MAKE_WORKER_PROTO(, BuildResult);
+MAKE_WORKER_PROTO(, KeyedBuildResult);
 MAKE_WORKER_PROTO(, std::optional<TrustedFlag>);
 
 MAKE_WORKER_PROTO(template<typename T>, std::vector<T>);

src/libutil/config-impl.hh

@@ -0,0 +1,71 @@
+#pragma once
+/**
+ * @file
+ *
+ * Template implementations (as opposed to mere declarations).
+ *
+ * One only needs to include this when one is declaring a
+ * `BaseClass<CustomType>` setting, or as derived class of such an
+ * instantiation.
+ */
+
+#include "config.hh"
+
+namespace nix {
+
+template<> struct BaseSetting<Strings>::trait
+{
+    static constexpr bool appendable = true;
+};
+template<> struct BaseSetting<StringSet>::trait
+{
+    static constexpr bool appendable = true;
+};
+template<> struct BaseSetting<StringMap>::trait
+{
+    static constexpr bool appendable = true;
+};
+template<> struct BaseSetting<std::set<ExperimentalFeature>>::trait
+{
+    static constexpr bool appendable = true;
+};
+
+template<typename T>
+struct BaseSetting<T>::trait
+{
+    static constexpr bool appendable = false;
+};
+
+template<typename T>
+bool BaseSetting<T>::isAppendable()
+{
+    return trait::appendable;
+}
+
+template<> void BaseSetting<Strings>::appendOrSet(Strings && newValue, bool append);
+template<> void BaseSetting<StringSet>::appendOrSet(StringSet && newValue, bool append);
+template<> void BaseSetting<StringMap>::appendOrSet(StringMap && newValue, bool append);
+template<> void BaseSetting<std::set<ExperimentalFeature>>::appendOrSet(std::set<ExperimentalFeature> && newValue, bool append);
+
+template<typename T>
+void BaseSetting<T>::appendOrSet(T && newValue, bool append)
+{
+    static_assert(!trait::appendable, "using default `appendOrSet` implementation with an appendable type");
+    assert(!append);
+    value = std::move(newValue);
+}
+
+template<typename T>
+void BaseSetting<T>::set(const std::string & str, bool append)
+{
+    if (experimentalFeatureSettings.isEnabled(experimentalFeature))
+        appendOrSet(parse(str), append);
+    else {
+        assert(experimentalFeature);
+        warn("Ignoring setting '%s' because experimental feature '%s' is not enabled",
+            name,
+            showExperimentalFeature(*experimentalFeature));
+    }
+}
+
+}

src/libutil/config.cc

@@ -3,6 +3,8 @@
 #include "abstract-setting-to-json.hh"
 #include "experimental-features.hh"
 
+#include "config-impl.hh"
+
 #include <nlohmann/json.hpp>
 
 namespace nix {
@@ -80,6 +82,8 @@ void Config::getSettings(std::map<std::string, SettingInfo> & res, bool overridd
 void AbstractConfig::applyConfig(const std::string & contents, const std::string & path) {
     unsigned int pos = 0;
 
+    std::vector<std::pair<std::string, std::string>> parsedContents;
+
     while (pos < contents.size()) {
         std::string line;
         while (pos < contents.size() && contents[pos] != '\n')
@@ -125,8 +129,21 @@ void AbstractConfig::applyConfig(const std::string & contents, const std::string
         auto i = tokens.begin();
         advance(i, 2);
 
-        set(name, concatStringsSep(" ", Strings(i, tokens.end()))); // FIXME: slow
+        parsedContents.push_back({
+            name,
+            concatStringsSep(" ", Strings(i, tokens.end())),
+        });
     };
+
+    // First apply experimental-feature related settings
+    for (auto & [name, value] : parsedContents)
+        if (name == "experimental-features" || name == "extra-experimental-features")
+            set(name, value);
+
+    // Then apply other settings
+    for (auto & [name, value] : parsedContents)
+        if (name != "experimental-features" && name != "extra-experimental-features")
+            set(name, value);
 }
 
 void AbstractConfig::applyConfigFile(const Path & path)
@@ -202,12 +219,6 @@ void AbstractSetting::convertToArg(Args & args, const std::string & category)
 {
 }
 
-template<typename T>
-bool BaseSetting<T>::isAppendable()
-{
-    return false;
-}
-
 template<typename T>
 void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
 {
@@ -231,9 +242,9 @@ void BaseSetting<T>::convertToArg(Args & args, const std::string & category)
         });
 }
 
-template<> void BaseSetting<std::string>::set(const std::string & str, bool append)
+template<> std::string BaseSetting<std::string>::parse(const std::string & str) const
 {
-    value = str;
+    return str;
 }
 
 template<> std::string BaseSetting<std::string>::to_string() const
@@ -242,11 +253,11 @@ template<> std::string BaseSetting<std::string>::to_string() const
 }
 
 template<typename T>
-void BaseSetting<T>::set(const std::string & str, bool append)
+T BaseSetting<T>::parse(const std::string & str) const
 {
     static_assert(std::is_integral<T>::value, "Integer required.");
     if (auto n = string2Int<T>(str))
-        value = *n;
+        return *n;
     else
         throw UsageError("setting '%s' has invalid value '%s'", name, str);
 }
@@ -258,12 +269,12 @@ std::string BaseSetting<T>::to_string() const
     return std::to_string(value);
 }
 
-template<> void BaseSetting<bool>::set(const std::string & str, bool append)
+template<> bool BaseSetting<bool>::parse(const std::string & str) const
 {
     if (str == "true" || str == "yes" || str == "1")
-        value = true;
+        return true;
     else if (str == "false" || str == "no" || str == "0")
-        value = false;
+        return false;
     else
         throw UsageError("Boolean setting '%s' has invalid value '%s'", name, str);
 }
@@ -291,16 +302,15 @@ template<> void BaseSetting<bool>::convertToArg(Args & args, const std::string &
     });
 }
 
-template<> void BaseSetting<Strings>::set(const std::string & str, bool append)
+template<> Strings BaseSetting<Strings>::parse(const std::string & str) const
 {
-    auto ss = tokenizeString<Strings>(str);
+    return tokenizeString<Strings>(str);
-    if (!append) value.clear();
-    for (auto & s : ss) value.push_back(std::move(s));
 }
 
-template<> bool BaseSetting<Strings>::isAppendable()
+template<> void BaseSetting<Strings>::appendOrSet(Strings && newValue, bool append)
 {
-    return true;
+    if (!append) value.clear();
+    for (auto && s : std::move(newValue)) value.push_back(std::move(s));
 }
 
 template<> std::string BaseSetting<Strings>::to_string() const
@@ -308,16 +318,16 @@ template<> std::string BaseSetting<Strings>::to_string() const
     return concatStringsSep(" ", value);
 }
 
-template<> void BaseSetting<StringSet>::set(const std::string & str, bool append)
+template<> StringSet BaseSetting<StringSet>::parse(const std::string & str) const
 {
-    if (!append) value.clear();
+    return tokenizeString<StringSet>(str);
-    for (auto & s : tokenizeString<StringSet>(str))
-        value.insert(s);
 }
 
-template<> bool BaseSetting<StringSet>::isAppendable()
+template<> void BaseSetting<StringSet>::appendOrSet(StringSet && newValue, bool append)
 {
-    return true;
+    if (!append) value.clear();
+    for (auto && s : std::move(newValue))
+        value.insert(s);
 }
 
 template<> std::string BaseSetting<StringSet>::to_string() const
@@ -325,21 +335,24 @@ template<> std::string BaseSetting<StringSet>::to_string() const
     return concatStringsSep(" ", value);
 }
 
-template<> void BaseSetting<std::set<ExperimentalFeature>>::set(const std::string & str, bool append)
+template<> std::set<ExperimentalFeature> BaseSetting<std::set<ExperimentalFeature>>::parse(const std::string & str) const
 {
-    if (!append) value.clear();
+    std::set<ExperimentalFeature> res;
     for (auto & s : tokenizeString<StringSet>(str)) {
         auto thisXpFeature = parseExperimentalFeature(s);
         if (thisXpFeature)
-            value.insert(thisXpFeature.value());
+            res.insert(thisXpFeature.value());
         else
             warn("unknown experimental feature '%s'", s);
     }
+    return res;
 }
 
-template<> bool BaseSetting<std::set<ExperimentalFeature>>::isAppendable()
+template<> void BaseSetting<std::set<ExperimentalFeature>>::appendOrSet(std::set<ExperimentalFeature> && newValue, bool append)
 {
-    return true;
+    if (!append) value.clear();
+    for (auto && s : std::move(newValue))
+        value.insert(s);
 }
 
 template<> std::string BaseSetting<std::set<ExperimentalFeature>>::to_string() const
@@ -350,20 +363,23 @@ template<> std::string BaseSetting<std::set<ExperimentalFeature>>::to_string() c
     return concatStringsSep(" ", stringifiedXpFeatures);
 }
 
-template<> void BaseSetting<StringMap>::set(const std::string & str, bool append)
+template<> StringMap BaseSetting<StringMap>::parse(const std::string & str) const
 {
-    if (!append) value.clear();
+    StringMap res;
     for (auto & s : tokenizeString<Strings>(str)) {
         auto eq = s.find_first_of('=');
         if (std::string::npos != eq)
-            value.emplace(std::string(s, 0, eq), std::string(s, eq + 1));
+            res.emplace(std::string(s, 0, eq), std::string(s, eq + 1));
         // else ignored
     }
+    return res;
 }
 
-template<> bool BaseSetting<StringMap>::isAppendable()
+template<> void BaseSetting<StringMap>::appendOrSet(StringMap && newValue, bool append)
 {
-    return true;
+    if (!append) value.clear();
+    for (auto && [k, v] : std::move(newValue))
+        value.emplace(std::move(k), std::move(v));
 }
 
 template<> std::string BaseSetting<StringMap>::to_string() const
@@ -387,15 +403,15 @@ template class BaseSetting<StringSet>;
 template class BaseSetting<StringMap>;
 template class BaseSetting<std::set<ExperimentalFeature>>;
 
-void PathSetting::set(const std::string & str, bool append)
+Path PathSetting::parse(const std::string & str) const
 {
     if (str == "") {
         if (allowEmpty)
-            value = "";
+            return "";
         else
             throw UsageError("setting '%s' cannot be empty", name);
     } else
-        value = canonPath(str);
+        return canonPath(str);
 }
 
 bool GlobalConfig::set(const std::string & name, const std::string & value)

src/libutil/config.hh

@@ -215,8 +215,11 @@ protected:
 
     virtual void set(const std::string & value, bool append = false) = 0;
 
-    virtual bool isAppendable()
+    /**
-    { return false; }
+     * Whether the type is appendable; i.e. whether the `append`
+     * parameter to `set()` is allowed to be `true`.
+     */
+    virtual bool isAppendable() = 0;
 
     virtual std::string to_string() const = 0;
 
@@ -241,6 +244,23 @@ protected:
     const T defaultValue;
     const bool documentDefault;
 
+    /**
+     * Parse the string into a `T`.
+     *
+     * Used by `set()`.
+     */
+    virtual T parse(const std::string & str) const;
+
+    /**
+     * Append or overwrite `value` with `newValue`.
+     *
+     * Some types to do not support appending in which case `append`
+     * should never be passed. The default handles this case.
+     *
+     * @param append Whether to append or overwrite.
+     */
+    virtual void appendOrSet(T && newValue, bool append);
+
 public:
 
     BaseSetting(const T & def,
@@ -268,9 +288,25 @@ public:
     template<typename U>
     void setDefault(const U & v) { if (!overridden) value = v; }
 
-    void set(const std::string & str, bool append = false) override;
+    /**
+     * Require any experimental feature the setting depends on
+     *
+     * Uses `parse()` to get the value from `str`, and `appendOrSet()`
+     * to set it.
+     */
+    void set(const std::string & str, bool append = false) override final;
 
-    bool isAppendable() override;
+    /**
+     * C++ trick; This is template-specialized to compile-time indicate whether
+     * the type is appendable.
+     */
+    struct trait;
+
+    /**
+     * Always defined based on the C++ magic
+     * with `trait` above.
+     */
+    bool isAppendable() override final;
 
     virtual void override(const T & v)
     {
@@ -336,7 +372,7 @@ public:
         options->addSetting(this);
     }
 
-    void set(const std::string & str, bool append = false) override;
+    Path parse(const std::string & str) const override;
 
     Path operator +(const char * p) const { return value + p; }
 

src/libutil/experimental-features.cc

@@ -12,7 +12,7 @@ struct ExperimentalFeatureDetails
     std::string_view description;
 };
 
-constexpr std::array<ExperimentalFeatureDetails, 11> xpFeatureDetails = {{
+constexpr std::array<ExperimentalFeatureDetails, 12> xpFeatureDetails = {{
     {
         .tag = Xp::CaDerivations,
         .name = "ca-derivations",
@@ -189,6 +189,16 @@ constexpr std::array<ExperimentalFeatureDetails, 11> xpFeatureDetails = {{
             runtime dependencies.
         )",
     },
+    {
+        .tag = Xp::DaemonTrustOverride,
+        .name = "daemon-trust-override",
+        .description = R"(
+            Allow forcing trusting or not trusting clients with
+            `nix-daemon`. This is useful for testing, but possibly also
+            useful for various experiments with `nix-daemon --stdio`
+            networking.
+        )",
+    },
 }};
 
 static_assert(

src/libutil/experimental-features.hh

@@ -28,6 +28,7 @@ enum struct ExperimentalFeature
     AutoAllocateUids,
     Cgroups,
     DiscardReferences,
+    DaemonTrustOverride,
 };
 
 /**

src/libutil/hash.cc

@@ -1,6 +1,7 @@
 #include <iostream>
 #include <cstring>
 
+#include <openssl/crypto.h>
 #include <openssl/md5.h>
 #include <openssl/sha.h>
 
@@ -16,7 +17,6 @@
 
 namespace nix {
 
-
 static size_t regularHashSize(HashType type) {
     switch (type) {
     case htMD5: return md5HashSize;

src/libutil/tests/config.cc

@@ -82,6 +82,7 @@ namespace nix {
             TestSetting() : AbstractSetting("test", "test", {}) {}
             void set(const std::string & value, bool append) override {}
             std::string to_string() const override { return {}; }
+            bool isAppendable() override { return false; }
         };
 
         Config config;
@@ -90,6 +91,7 @@ namespace nix {
         ASSERT_FALSE(config.set("test", "value"));
         config.addSetting(&setting);
         ASSERT_TRUE(config.set("test", "value"));
+        ASSERT_FALSE(config.set("extra-test", "value"));
     }
 
     TEST(Config, withInitialValue) {

src/libutil/util.cc

@@ -47,6 +47,9 @@ extern char * * environ __attribute__((weak));
 
 namespace nix {
 
+void initLibUtil() {
+}
+
 std::optional<std::string> getEnv(const std::string & key)
 {
     char * value = getenv(key.c_str());
@@ -1744,13 +1747,39 @@ void triggerInterrupt()
 }
 
 static sigset_t savedSignalMask;
+static bool savedSignalMaskIsSet = false;
+
+void setChildSignalMask(sigset_t * sigs)
+{
+    assert(sigs); // C style function, but think of sigs as a reference
+
+#if _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
+    sigemptyset(&savedSignalMask);
+    // There's no "assign" or "copy" function, so we rely on (math) idempotence
+    // of the or operator: a or a = a.
+    sigorset(&savedSignalMask, sigs, sigs);
+#else
+    // Without sigorset, our best bet is to assume that sigset_t is a type that
+    // can be assigned directly, such as is the case for a sigset_t defined as
+    // an integer type.
+    savedSignalMask = *sigs;
+#endif
+
+    savedSignalMaskIsSet = true;
+}
+
+void saveSignalMask() {
+    if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask))
+        throw SysError("querying signal mask");
+
+    savedSignalMaskIsSet = true;
+}
 
 void startSignalHandlerThread()
 {
     updateWindowSize();
 
-    if (sigprocmask(SIG_BLOCK, nullptr, &savedSignalMask))
+    saveSignalMask();
-        throw SysError("querying signal mask");
 
     sigset_t set;
     sigemptyset(&set);
@@ -1767,6 +1796,20 @@ void startSignalHandlerThread()
 
 static void restoreSignals()
 {
+    // If startSignalHandlerThread wasn't called, that means we're not running
+    // in a proper libmain process, but a process that presumably manages its
+    // own signal handlers. Such a process should call either
+    //  - initNix(), to be a proper libmain process
+    //  - startSignalHandlerThread(), to resemble libmain regarding signal
+    //    handling only
+    //  - saveSignalMask(), for processes that define their own signal handling
+    //    thread
+    // TODO: Warn about this? Have a default signal mask? The latter depends on
+    //       whether we should generally inherit signal masks from the caller.
+    //       I don't know what the larger unix ecosystem expects from us here.
+    if (!savedSignalMaskIsSet)
+        return;
+
     if (sigprocmask(SIG_SETMASK, &savedSignalMask, nullptr))
         throw SysError("restoring signals");
 }

src/libutil/util.hh

@@ -32,6 +32,7 @@ namespace nix {
 struct Sink;
 struct Source;
 
+void initLibUtil();
 
 /**
  * The system for which Nix is compiled.
@@ -445,6 +446,8 @@ void setStackSize(size_t stackSize);
 /**
  * Restore the original inherited Unix process context (such as signal
  * masks, stack size).
+
+ * See startSignalHandlerThread(), saveSignalMask().
  */
 void restoreProcessContext(bool restoreMounts = true);
 
@@ -814,9 +817,26 @@ class Callback;
 /**
  * Start a thread that handles various signals. Also block those signals
  * on the current thread (and thus any threads created by it).
+ * Saves the signal mask before changing the mask to block those signals.
+ * See saveSignalMask().
  */
 void startSignalHandlerThread();
 
+/**
+ * Saves the signal mask, which is the signal mask that nix will restore
+ * before creating child processes.
+ * See setChildSignalMask() to set an arbitrary signal mask instead of the
+ * current mask.
+ */
+void saveSignalMask();
+
+/**
+ * Sets the signal mask. Like saveSignalMask() but for a signal set that doesn't
+ * necessarily match the current thread's mask.
+ * See saveSignalMask() to set the saved mask to the current mask.
+ */
+void setChildSignalMask(sigset_t *sigs);
+
 struct InterruptCallback
 {
     virtual ~InterruptCallback() { };

src/nix-env/nix-env.cc

@@ -962,7 +962,7 @@ static void queryJSON(Globals & globals, std::vector<DrvInfo> & elems, bool prin
                         printError("derivation '%s' has invalid meta attribute '%s'", i.queryName(), j);
                         metaObj[j] = nullptr;
                     } else {
-                        PathSet context;
+                        NixStringContext context;
                         metaObj[j] = printValueAsJSON(*globals.state, true, *v, noPos, context);
                     }
                 }

src/nix-env/user-env.cc

@@ -119,9 +119,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     /* Construct a Nix expression that calls the user environment
        builder with the manifest as argument. */
     auto attrs = state.buildBindings(3);
-    attrs.alloc("manifest").mkString(
+    state.mkStorePathString(manifestFile, attrs.alloc("manifest"));
-        state.store->printStorePath(manifestFile),
-        {state.store->printStorePath(manifestFile)});
     attrs.insert(state.symbols.create("derivations"), &manifest);
     Value args;
     args.mkAttrs(attrs);
@@ -132,7 +130,7 @@ bool createUserEnv(EvalState & state, DrvInfos & elems,
     /* Evaluate it. */
     debug("evaluating user environment builder");
     state.forceValue(topLevel, [&]() { return topLevel.determinePos(noPos); });
-    PathSet context;
+    NixStringContext context;
     Attr & aDrvPath(*topLevel.attrs->find(state.sDrvPath));
     auto topLevelDrv = state.coerceToStorePath(aDrvPath.pos, *aDrvPath.value, context, "");
     Attr & aOutPath(*topLevel.attrs->find(state.sOutPath));

src/nix-instantiate/nix-instantiate.cc

@@ -43,7 +43,7 @@ void processExpr(EvalState & state, const Strings & attrPaths,
         Value & v(*findAlongAttrPath(state, i, autoArgs, vRoot).first);
         state.forceValue(v, [&]() { return v.determinePos(noPos); });
 
-        PathSet context;
+        NixStringContext context;
         if (evalOnly) {
             Value vRes;
             if (autoArgs.empty())

src/nix-store/nix-store.cc

@@ -204,10 +204,10 @@ static void opAddFixed(Strings opFlags, Strings opArgs)
 /* Hack to support caching in `nix-prefetch-url'. */
 static void opPrintFixedPath(Strings opFlags, Strings opArgs)
 {
-    auto recursive = FileIngestionMethod::Flat;
+    auto method = FileIngestionMethod::Flat;
 
     for (auto i : opFlags)
-        if (i == "--recursive") recursive = FileIngestionMethod::Recursive;
+        if (i == "--recursive") method = FileIngestionMethod::Recursive;
         else throw UsageError("unknown flag '%1%'", i);
 
     if (opArgs.size() != 3)
@@ -218,7 +218,13 @@ static void opPrintFixedPath(Strings opFlags, Strings opArgs)
     std::string hash = *i++;
     std::string name = *i++;
 
-    cout << fmt("%s\n", store->printStorePath(store->makeFixedOutputPath(recursive, Hash::parseAny(hash, hashAlgo), name)));
+    cout << fmt("%s\n", store->printStorePath(store->makeFixedOutputPath(name, FixedOutputInfo {
+        .hash = {
+            .method = method,
+            .hash = Hash::parseAny(hash, hashAlgo),
+        },
+        .references = {},
+    })));
 }
 
 
@@ -935,7 +941,10 @@ static void opServe(Strings opFlags, Strings opArgs)
                 if (GET_PROTOCOL_MINOR(clientVersion) >= 3)
                     out << status.timesBuilt << status.isNonDeterministic << status.startTime << status.stopTime;
                 if (GET_PROTOCOL_MINOR(clientVersion) >= 6) {
-                    worker_proto::write(*store, out, status.builtOutputs);
+                    DrvOutputs builtOutputs;
+                    for (auto & [output, realisation] : status.builtOutputs)
+                        builtOutputs.insert_or_assign(realisation.id, realisation);
+                    worker_proto::write(*store, out, builtOutputs);
                 }
 
                 break;
@@ -964,7 +973,7 @@ static void opServe(Strings opFlags, Strings opArgs)
                 info.references = worker_proto::read(*store, in, Phantom<StorePathSet> {});
                 in >> info.registrationTime >> info.narSize >> info.ultimate;
                 info.sigs = readStrings<StringSet>(in);
-                info.ca = parseContentAddressOpt(readString(in));
+                info.ca = ContentAddress::parseOpt(readString(in));
 
                 if (info.narSize == 0)
                     throw Error("narInfo is too old and missing the narSize field");

src/nix/add-to-store.cc

@@ -42,14 +42,18 @@ struct CmdAddToStore : MixDryRun, StoreCommand
         }
 
         ValidPathInfo info {
-            store->makeFixedOutputPath(ingestionMethod, hash, *namePart),
+            *store,
+            std::move(*namePart),
+            FixedOutputInfo {
+                .hash = {
+                    .method = std::move(ingestionMethod),
+                    .hash = std::move(hash),
+                },
+                .references = {},
+            },
             narHash,
         };
         info.narSize = sink.s.size();
-        info.ca = std::optional { FixedOutputHash {
-            .method = ingestionMethod,
-            .hash = hash,
-        } };
 
         if (!dryRun) {
             auto source = StringSource(sink.s);

src/nix/bundle.cc

@@ -98,7 +98,7 @@ struct CmdBundle : InstallableValueCommand
         if (!attr1)
             throw Error("the bundler '%s' does not produce a derivation", bundler.what());
 
-        PathSet context2;
+        NixStringContext context2;
         auto drvPath = evalState->coerceToStorePath(attr1->pos, *attr1->value, context2, "");
 
         auto attr2 = vRes->attrs->get(evalState->sOutPath);

src/nix/daemon.cc

@@ -273,8 +273,12 @@ static std::pair<TrustedFlag, std::string> authPeer(const PeerInfo & peer)
 /**
  * Run a server. The loop opens a socket and accepts new connections from that
  * socket.
+ *
+ * @param forceTrustClientOpt If present, force trusting or not trusted
+ * the client. Otherwise, decide based on the authentication settings
+ * and user credentials (from the unix domain socket).
  */
-static void daemonLoop()
+static void daemonLoop(std::optional<TrustedFlag> forceTrustClientOpt)
 {
     if (chdir("/") == -1)
         throw SysError("cannot change current directory");
@@ -317,9 +321,18 @@ static void daemonLoop()
 
             closeOnExec(remote.get());
 
-            PeerInfo peer = getPeerInfo(remote.get());
+            PeerInfo peer { .pidKnown = false };
-            auto [_trusted, user] = authPeer(peer);
+            TrustedFlag trusted;
-            auto trusted = _trusted;
+            std::string user;
+
+            if (forceTrustClientOpt)
+                trusted = *forceTrustClientOpt;
+            else {
+                peer = getPeerInfo(remote.get());
+                auto [_trusted, _user] = authPeer(peer);
+                trusted = _trusted;
+                user = _user;
+            };
 
             printInfo((std::string) "accepted connection from pid %1%, user %2%" + (trusted ? " (trusted)" : ""),
                 peer.pidKnown ? std::to_string(peer.pid) : "<unknown>",
@@ -410,38 +423,47 @@ static void forwardStdioConnection(RemoteStore & store) {
  * Unlike `forwardStdioConnection()` we do process commands ourselves in
  * this case, not delegating to another daemon.
  *
- * @note `Trusted` is unconditionally passed because in this mode we
+ * @param trustClient Whether to trust the client. Forwarded directly to
- * blindly trust the standard streams. Limiting access to those is
+ * `processConnection()`.
- * explicitly not `nix-daemon`'s responsibility.
  */
-static void processStdioConnection(ref<Store> store)
+static void processStdioConnection(ref<Store> store, TrustedFlag trustClient)
 {
     FdSource from(STDIN_FILENO);
     FdSink to(STDOUT_FILENO);
-    processConnection(store, from, to, Trusted, NotRecursive);
+    processConnection(store, from, to, trustClient, NotRecursive);
 }
 
 /**
  * Entry point shared between the new CLI `nix daemon` and old CLI
  * `nix-daemon`.
+ *
+ * @param forceTrustClientOpt See `daemonLoop()` and the parameter with
+ * the same name over there for details.
  */
-static void runDaemon(bool stdio)
+static void runDaemon(bool stdio, std::optional<TrustedFlag> forceTrustClientOpt)
 {
     if (stdio) {
         auto store = openUncachedStore();
 
-        if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>())
+        // If --force-untrusted is passed, we cannot forward the connection and
+        // must process it ourselves (before delegating to the next store) to
+        // force untrusting the client.
+        if (auto remoteStore = store.dynamic_pointer_cast<RemoteStore>(); remoteStore && (!forceTrustClientOpt || *forceTrustClientOpt != NotTrusted))
             forwardStdioConnection(*remoteStore);
         else
-            processStdioConnection(store);
+            // `Trusted` is passed in the auto (no override case) because we
+            // cannot see who is on the other side of a plain pipe. Limiting
+            // access to those is explicitly not `nix-daemon`'s responsibility.
+            processStdioConnection(store, forceTrustClientOpt.value_or(Trusted));
     } else
-        daemonLoop();
+        daemonLoop(forceTrustClientOpt);
 }
 
 static int main_nix_daemon(int argc, char * * argv)
 {
     {
         auto stdio = false;
+        std::optional<TrustedFlag> isTrustedOpt = std::nullopt;
 
         parseCmdLine(argc, argv, [&](Strings::iterator & arg, const Strings::iterator & end) {
             if (*arg == "--daemon")
@@ -452,11 +474,20 @@ static int main_nix_daemon(int argc, char * * argv)
                 printVersion("nix-daemon");
             else if (*arg == "--stdio")
                 stdio = true;
-            else return false;
+            else if (*arg == "--force-trusted") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = Trusted;
+            } else if (*arg == "--force-untrusted") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = NotTrusted;
+            } else if (*arg == "--default-trust") {
+                experimentalFeatureSettings.require(Xp::DaemonTrustOverride);
+                isTrustedOpt = std::nullopt;
+            } else return false;
             return true;
         });
 
-        runDaemon(stdio);
+        runDaemon(stdio, isTrustedOpt);
 
         return 0;
     }
@@ -482,7 +513,7 @@ struct CmdDaemon : StoreCommand
 
     void run(ref<Store> store) override
     {
-        runDaemon(false);
+        runDaemon(false, std::nullopt);
     }
 };
 

src/nix/eval.cc

@@ -62,7 +62,7 @@ struct CmdEval : MixJSON, InstallableValueCommand, MixReadOnlyOption
         auto state = getEvalState();
 
         auto [v, pos] = installable->toValue(*state);
-        PathSet context;
+        NixStringContext context;
 
         if (apply) {
             auto vApply = state->allocValue();

src/nix/flake.cc

@@ -438,7 +438,7 @@ struct CmdFlakeCheck : FlakeCommand
 
                 if (auto attr = v.attrs->get(state->symbols.create("path"))) {
                     if (attr->name == state->symbols.create("path")) {
-                        PathSet context;
+                        NixStringContext context;
                         auto path = state->coerceToPath(attr->pos, *attr->value, context, "");
                         if (!path.pathExists())
                             throw Error("template '%s' refers to a non-existent path '%s'", attrPath, path);

src/nix/flake.md

@@ -381,10 +381,12 @@ The following attributes are supported in `flake.nix`:
 
 * `nixConfig`: a set of `nix.conf` options to be set when evaluating any
   part of a flake. In the interests of security, only a small set of
-  whitelisted options (currently `bash-prompt`, `bash-prompt-prefix`,
+  set of options is allowed to be set without confirmation so long as [`accept-flake-config`](@docroot@/command-ref/conf-file.md#conf-accept-flake-config) is not enabled in the global configuration:
-  `bash-prompt-suffix`, and `flake-registry`) are allowed to be set without
+   - [`bash-prompt`](@docroot@/command-ref/conf-file.md#conf-bash-prompt)
-  confirmation so long as `accept-flake-config` is not set in the global
+   - [`bash-prompt-prefix`](@docroot@/command-ref/conf-file.md#conf-bash-prompt-prefix)
-  configuration.
+   - [`bash-prompt-suffix`](@docroot@/command-ref/conf-file.md#conf-bash-prompt-suffix)
+   - [`flake-registry`](@docroot@/command-ref/conf-file.md#conf-flake-registry)
+   - [`commit-lockfile-summary`](@docroot@/command-ref/conf-file.md#conf-commit-lockfile-summary)
 
 ## Flake inputs
 

src/nix/prefetch.cc

@@ -70,7 +70,13 @@ std::tuple<StorePath, Hash> prefetchFile(
        the store. */
     if (expectedHash) {
         hashType = expectedHash->type;
-        storePath = store->makeFixedOutputPath(ingestionMethod, *expectedHash, *name);
+        storePath = store->makeFixedOutputPath(*name, FixedOutputInfo {
+            .hash = {
+                .method = ingestionMethod,
+                .hash = *expectedHash,
+            },
+            .references = {},
+        });
         if (store->isValidPath(*storePath))
             hash = expectedHash;
         else
@@ -121,7 +127,7 @@ std::tuple<StorePath, Hash> prefetchFile(
         auto info = store->addToStoreSlow(*name, tmpFile, ingestionMethod, hashType, expectedHash);
         storePath = info.path;
         assert(info.ca);
-        hash = getContentAddressHash(*info.ca);
+        hash = info.ca->getHash();
     }
 
     return {storePath.value(), hash.value()};

src/nix/profile.cc

@@ -200,12 +200,22 @@ struct ProfileManifest
         auto narHash = hashString(htSHA256, sink.s);
 
         ValidPathInfo info {
-            store->makeFixedOutputPath(FileIngestionMethod::Recursive, narHash, "profile", references),
+            *store,
+            "profile",
+            FixedOutputInfo {
+                .hash = {
+                    .method = FileIngestionMethod::Recursive,
+                    .hash = narHash,
+                },
+                .references = {
+                    .others = std::move(references),
+                    // profiles never refer to themselves
+                    .self = false,
+                },
+            },
             narHash,
         };
-        info.references = std::move(references);
         info.narSize = sink.s.size();
-        info.ca = FixedOutputHash { .method = FileIngestionMethod::Recursive, .hash = info.narHash };
 
         StringSource source(sink.s);
         store->addToStore(info, source);

tests/build-remote-trustless-after.sh

@@ -0,0 +1,2 @@
+outPath=$(readlink -f $TEST_ROOT/result)
+grep 'FOO BAR BAZ' ${remoteDir}/${outPath}

tests/build-remote-trustless-should-fail-0.sh

@@ -0,0 +1,29 @@
+source common.sh
+
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+# We first build a dependency of the derivation we eventually want to
+# build.
+nix-build build-hook.nix -A passthru.input2 \
+  -o "$TEST_ROOT/input2" \
+  --arg busybox "$busybox" \
+  --store "$TEST_ROOT/local" \
+  --option system-features bar
+
+# Now when we go to build that downstream derivation, Nix will fail
+# because we cannot trustlessly build input-addressed derivations with
+# `inputDrv` dependencies.
+
+file=build-hook.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+
+expectStderr 1 source build-remote-trustless.sh \
+    | grepQuiet "you are not privileged to build input-addressed derivations"

tests/build-remote-trustless-should-pass-0.sh

@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us
+file=build-hook.nix
+prog=nix-store
+proto=ssh
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless-should-pass-1.sh

@@ -0,0 +1,9 @@
+source common.sh
+
+# Remote trusts us
+file=build-hook.nix
+prog=nix-daemon
+proto=ssh-ng
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless-should-pass-3.sh

@@ -0,0 +1,14 @@
+source common.sh
+
+enableFeatures "daemon-trust-override"
+
+restartDaemon
+
+# Remote doesn't trusts us, but this is fine because we are only
+# building (fixed) CA derivations.
+file=build-hook-ca-fixed.nix
+prog=$(readlink -e ./nix-daemon-untrusting.sh)
+proto=ssh-ng
+
+source build-remote-trustless.sh
+source build-remote-trustless-after.sh

tests/build-remote-trustless.sh

@@ -0,0 +1,14 @@
+requireSandboxSupport
+[[ $busybox =~ busybox ]] || skipTest "no busybox"
+
+unset NIX_STORE_DIR
+unset NIX_STATE_DIR
+
+remoteDir=$TEST_ROOT/remote
+
+# Note: ssh{-ng}://localhost bypasses ssh. See tests/build-remote.sh for
+# more details.
+nix-build $file -o $TEST_ROOT/result --max-jobs 0 \
+  --arg busybox $busybox \
+  --store $TEST_ROOT/local \
+  --builders "$proto://localhost?remote-program=$prog&remote-store=${remoteDir}%3Fsystem-features=foo%20bar%20baz - - 1 1 foo,bar,baz"

tests/ca/derivation-json.sh

@@ -16,6 +16,9 @@ drvPath3=$(nix derivation add --dry-run < $TEST_HOME/foo.json)
 # With --dry-run nothing is actually written
 [[ ! -e "$drvPath3" ]]
 
+# But the JSON is rejected without the experimental feature
+expectStderr 1 nix derivation add < $TEST_HOME/foo.json --experimental-features nix-command | grepQuiet "experimental Nix feature 'ca-derivations' is disabled"
+
 # Without --dry-run it is actually written
 drvPath4=$(nix derivation add < $TEST_HOME/foo.json)
 [[ "$drvPath4" = "$drvPath3" ]]

tests/experimental-features.sh

@@ -23,20 +23,64 @@ source common.sh
 # # Medium case, the configuration effects --help
 # grep_both_ways store gc --help
 
-expect 1 nix --experimental-features 'nix-command' show-config --flake-registry 'https://no'
+# Test settings that are gated on experimental features; the setting is ignored
-nix --experimental-features 'nix-command flakes' show-config --flake-registry 'https://no'
+# with a warning if the experimental feature is not enabled. The order of the
+# `setting = value` lines in the configuration should not matter.
+
+# 'flakes' experimental-feature is disabled before, ignore and warn
+NIX_CONFIG='
+  experimental-features = nix-command
+  accept-flake-config = true
+' nix show-config accept-flake-config 1>$TEST_ROOT/stdout 2>$TEST_ROOT/stderr
+grepQuiet "false" $TEST_ROOT/stdout
+grepQuiet "Ignoring setting 'accept-flake-config' because experimental feature 'flakes' is not enabled" $TEST_ROOT/stderr
+
+# 'flakes' experimental-feature is disabled after, ignore and warn
+NIX_CONFIG='
+  accept-flake-config = true
+  experimental-features = nix-command
+' nix show-config accept-flake-config 1>$TEST_ROOT/stdout 2>$TEST_ROOT/stderr
+grepQuiet "false" $TEST_ROOT/stdout
+grepQuiet "Ignoring setting 'accept-flake-config' because experimental feature 'flakes' is not enabled" $TEST_ROOT/stderr
+
+# 'flakes' experimental-feature is enabled before, process
+NIX_CONFIG='
+  experimental-features = nix-command flakes
+  accept-flake-config = true
+' nix show-config accept-flake-config 1>$TEST_ROOT/stdout 2>$TEST_ROOT/stderr
+grepQuiet "true" $TEST_ROOT/stdout
+grepQuietInverse "Ignoring setting 'accept-flake-config'" $TEST_ROOT/stderr
+
+# 'flakes' experimental-feature is enabled after, process
+NIX_CONFIG='
+  accept-flake-config = true
+  experimental-features = nix-command flakes
+' nix show-config accept-flake-config 1>$TEST_ROOT/stdout 2>$TEST_ROOT/stderr
+grepQuiet "true" $TEST_ROOT/stdout
+grepQuietInverse "Ignoring setting 'accept-flake-config'" $TEST_ROOT/stderr
+
+function exit_code_both_ways {
+    expect 1 nix --experimental-features 'nix-command' "$@" 1>/dev/null
+    nix --experimental-features 'nix-command flakes' "$@" 1>/dev/null
+
+    # Also, the order should not matter
+    expect 1 nix "$@" --experimental-features 'nix-command' 1>/dev/null
+    nix "$@" --experimental-features 'nix-command flakes' 1>/dev/null
+}
+
+exit_code_both_ways show-config --flake-registry 'https://no'
 
 # Double check these are stable
-nix --experimental-features '' --help
+nix --experimental-features '' --help 1>/dev/null
-nix --experimental-features '' doctor --help
+nix --experimental-features '' doctor --help 1>/dev/null
-nix --experimental-features '' repl --help
+nix --experimental-features '' repl --help 1>/dev/null
-nix --experimental-features '' upgrade-nix --help
+nix --experimental-features '' upgrade-nix --help 1>/dev/null
 
 # These 3 arguments are currently given to all commands, which is wrong (as not
 # all care). To deal with fixing later, we simply make them require the
 # nix-command experimental features --- it so happens that the commands we wish
 # stabilizing to do not need them anyways.
 for arg in '--print-build-logs' '--offline' '--refresh'; do
-    nix --experimental-features 'nix-command' "$arg" --help
+    nix --experimental-features 'nix-command' "$arg" --help 1>/dev/null
-    ! nix --experimental-features '' "$arg" --help
+    expect 1 nix --experimental-features '' "$arg" --help 1>/dev/null
 done

tests/impure-derivations.sh

@@ -10,6 +10,15 @@ clearStore
 # Basic test of impure derivations: building one a second time should not use the previous result.
 printf 0 > $TEST_ROOT/counter
 
+# `nix derivation add` with impure derivations work
+drvPath=$(nix-instantiate ./impure-derivations.nix -A impure)
+nix derivation show $drvPath | jq .[] > $TEST_HOME/impure-drv.json
+drvPath2=$(nix derivation add < $TEST_HOME/impure-drv.json)
+[[ "$drvPath" = "$drvPath2" ]]
+
+# But only with the experimental feature!
+expectStderr 1 nix derivation add < $TEST_HOME/impure-drv.json --experimental-features nix-command | grepQuiet "experimental Nix feature 'impure-derivations' is disabled"
+
 nix build --dry-run --json --file ./impure-derivations.nix impure.all
 json=$(nix build -L --no-link --json --file ./impure-derivations.nix impure.all)
 path1=$(echo $json | jq -r .[].outputs.out)

tests/local.mk

@@ -70,6 +70,10 @@ nix_tests = \
   check-reqs.sh \
   build-remote-content-addressed-fixed.sh \
   build-remote-content-addressed-floating.sh \
+  build-remote-trustless-should-pass-0.sh \
+  build-remote-trustless-should-pass-1.sh \
+  build-remote-trustless-should-pass-3.sh \
+  build-remote-trustless-should-fail-0.sh \
   nar-access.sh \
   pure-eval.sh \
   eval.sh \

tests/nix-daemon-untrusting.sh

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+exec nix-daemon --force-untrusted "$@"

tests/recursive.nix

@@ -0,0 +1,56 @@
+with import ./config.nix;
+
+mkDerivation rec {
+  name = "recursive";
+  dummy = builtins.toFile "dummy" "bla bla";
+  SHELL = shell;
+
+  # Note: this is a string without context.
+  unreachable = builtins.getEnv "unreachable";
+
+  NIX_TESTS_CA_BY_DEFAULT = builtins.getEnv "NIX_TESTS_CA_BY_DEFAULT";
+
+  requiredSystemFeatures = [ "recursive-nix" ];
+
+  buildCommand = ''
+    mkdir $out
+    opts="--experimental-features nix-command ${if (NIX_TESTS_CA_BY_DEFAULT == "1") then "--extra-experimental-features ca-derivations" else ""}"
+
+    PATH=${builtins.getEnv "NIX_BIN_DIR"}:$PATH
+
+    # Check that we can query/build paths in our input closure.
+    nix $opts path-info $dummy
+    nix $opts build $dummy
+
+    # Make sure we cannot query/build paths not in out input closure.
+    [[ -e $unreachable ]]
+    (! nix $opts path-info $unreachable)
+    (! nix $opts build $unreachable)
+
+    # Add something to the store.
+    echo foobar > foobar
+    foobar=$(nix $opts store add-path ./foobar)
+
+    nix $opts path-info $foobar
+    nix $opts build $foobar
+
+    # Add it to our closure.
+    ln -s $foobar $out/foobar
+
+    [[ $(nix $opts path-info --all | wc -l) -eq 4 ]]
+
+    # Build a derivation.
+    nix $opts build -L --impure --expr '
+      with import ${./config.nix};
+      mkDerivation {
+        name = "inner1";
+        buildCommand = "echo $fnord blaat > $out";
+        fnord = builtins.toFile "fnord" "fnord";
+      }
+    '
+
+    [[ $(nix $opts path-info --json ./result) =~ fnord ]]
+
+    ln -s $(nix $opts path-info ./result) $out/inner1
+  '';
+}