Squashed get CA derivations building

src/libexpr/get-drvs.cc

@@ -39,7 +39,9 @@ DrvInfo::DrvInfo(EvalState & state, ref<Store> store, const std::string & drvPat
     if (i == drv.outputs.end())
         throw Error("derivation '%s' does not have output '%s'", store->printStorePath(drvPath), outputName);
 
-    outPath = store->printStorePath(i->second.path(*store, drv.name));
+    auto optStorePath = i->second.pathOpt(*store, drv.name);
+    if (optStorePath)
+        outPath = store->printStorePath(*optStorePath);
 }
 
 
@@ -77,12 +79,15 @@ string DrvInfo::queryDrvPath() const
 
 string DrvInfo::queryOutPath() const
 {
-    if (outPath == "" && attrs) {
+    if (!outPath && attrs) {
         Bindings::iterator i = attrs->find(state->sOutPath);
         PathSet context;
-        outPath = i != attrs->end() ? state->coerceToPath(*i->pos, *i->value, context) : "";
+        if (i != attrs->end())
+            outPath = state->coerceToPath(*i->pos, *i->value, context);
     }
-    return outPath;
+    if (!outPath)
+        throw UnimplementedError("CA derivations are not yet supported");
+    return *outPath;
 }
 
 

src/libexpr/get-drvs.hh

@@ -20,7 +20,7 @@ private:
     mutable string name;
     mutable string system;
     mutable string drvPath;
-    mutable string outPath;
+    mutable std::optional<string> outPath;
     mutable string outputName;
     Outputs outputs;
 

src/libexpr/primops.cc

@@ -44,16 +44,6 @@ void EvalState::realiseContext(const PathSet & context)
             throw InvalidPathError(store->printStorePath(ctx));
         if (!outputName.empty() && ctx.isDerivation()) {
             drvs.push_back(StorePathWithOutputs{ctx, {outputName}});
-
-            /* Add the output of this derivation to the allowed
-               paths. */
-            if (allowedPaths) {
-                auto drv = store->derivationFromPath(ctx);
-                DerivationOutputs::iterator i = drv.outputs.find(outputName);
-                if (i == drv.outputs.end())
-                    throw Error("derivation '%s' does not have an output named '%s'", ctxS, outputName);
-                allowedPaths->insert(store->printStorePath(i->second.path(*store, drv.name)));
-            }
         }
     }
 
@@ -69,8 +59,38 @@ void EvalState::realiseContext(const PathSet & context)
     store->queryMissing(drvs, willBuild, willSubstitute, unknown, downloadSize, narSize);
 
     store->buildPaths(drvs);
+
+    /* Add the output of this derivations to the allowed
+       paths. */
+    if (allowedPaths) {
+        for (auto & [drvPath, outputs] : drvs) {
+            auto outputPaths = store->queryDerivationOutputMapAssumeTotal(drvPath);
+            for (auto & outputName : outputs) {
+                if (outputPaths.count(outputName) == 0)
+                    throw Error("derivation '%s' does not have an output named '%s'",
+                            store->printStorePath(drvPath), outputName);
+                allowedPaths->insert(store->printStorePath(outputPaths.at(outputName)));
+            }
+        }
+    }
 }
 
+static void mkOutputString(EvalState & state, Value & v,
+    const StorePath & drvPath, const BasicDerivation & drv,
+    std::pair<string, DerivationOutput> o)
+{
+    auto optOutputPath = o.second.pathOpt(*state.store, drv.name);
+    mkString(
+        *state.allocAttr(v, state.symbols.create(o.first)),
+        state.store->printStorePath(optOutputPath
+            ? *optOutputPath
+            /* Downstream we would substitute this for an actual path once
+               we build the floating CA derivation */
+            /* FIXME: we need to depend on the basic derivation, not
+               derivation */
+            : downstreamPlaceholder(*state.store, drvPath, o.first)),
+        {"!" + o.first + "!" + state.store->printStorePath(drvPath)});
+}
 
 /* Load and evaluate an expression from path specified by the
    argument. */
@@ -114,8 +134,7 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
         unsigned int outputs_index = 0;
 
         for (const auto & o : drv.outputs) {
-            v2 = state.allocAttr(w, state.symbols.create(o.first));
+            mkOutputString(state, w, storePath, drv, o);
-            mkString(*v2, state.store->printStorePath(o.second.path(*state.store, drv.name)), {"!" + o.first + "!" + path});
             outputsVal->listElems()[outputs_index] = state.allocValue();
             mkString(*(outputsVal->listElems()[outputs_index++]), o.first);
         }
@@ -846,16 +865,18 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
 
     /* Optimisation, but required in read-only mode! because in that
        case we don't actually write store derivations, so we can't
-       read them later. */
+       read them later.
+
+       However, we don't bother doing this for floating CA derivations because
+       their "hash modulo" is indeterminate until built. */
+    if (drv.type() != DerivationType::CAFloating)
         drvHashes.insert_or_assign(drvPath,
             hashDerivationModulo(*state.store, Derivation(drv), false));
 
     state.mkAttrs(v, 1 + drv.outputs.size());
     mkString(*state.allocAttr(v, state.sDrvPath), drvPathS, {"=" + drvPathS});
-    for (auto & i : drv.outputs) {
+    for (auto & i : drv.outputs)
-        mkString(*state.allocAttr(v, state.symbols.create(i.first)),
+        mkOutputString(state, v, drvPath, drv, i);
-            state.store->printStorePath(i.second.path(*state.store, drv.name)), {"!" + i.first + "!" + drvPathS});
-    }
     v.attrs->sort();
 }
 

src/libstore/derivations.cc

@@ -15,7 +15,8 @@ std::optional<StorePath> DerivationOutput::pathOpt(const Store & store, std::str
         },
         [&](DerivationOutputCAFixed dof) -> std::optional<StorePath> {
             return {
-                store.makeFixedOutputPath(dof.hash.method, dof.hash.hash, drvName)
+                // FIXME if we intend to support multiple CA outputs.
+                dof.path(store, drvName, "out")
             };
         },
         [](DerivationOutputCAFloating dof) -> std::optional<StorePath> {
@@ -25,6 +26,13 @@ std::optional<StorePath> DerivationOutput::pathOpt(const Store & store, std::str
 }
 
 
+StorePath DerivationOutputCAFixed::path(const Store & store, std::string_view drvName, std::string_view outputName) const {
+    return store.makeFixedOutputPath(
+        hash.method, hash.hash,
+        outputPathName(drvName, outputName));
+}
+
+
 bool derivationIsCA(DerivationType dt) {
     switch (dt) {
     case DerivationType::InputAddressed: return false;
@@ -106,12 +114,15 @@ static string parseString(std::istream & str)
     return res;
 }
 
+static void validatePath(std::string_view s) {
+    if (s.size() == 0 || s[0] != '/')
+        throw FormatError("bad path '%1%' in derivation", s);
+}
 
 static Path parsePath(std::istream & str)
 {
-    string s = parseString(str);
+    auto s = parseString(str);
-    if (s.size() == 0 || s[0] != '/')
+    validatePath(s);
-        throw FormatError("bad path '%1%' in derivation", s);
     return s;
 }
 
@@ -141,7 +152,7 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 
 static DerivationOutput parseDerivationOutput(const Store & store, std::istringstream & str)
 {
-    expect(str, ","); auto path = store.parseStorePath(parsePath(str));
+    expect(str, ","); auto pathS = parseString(str);
     expect(str, ","); auto hashAlgo = parseString(str);
     expect(str, ","); const auto hash = parseString(str);
     expect(str, ")");
@@ -152,30 +163,35 @@ static DerivationOutput parseDerivationOutput(const Store & store, std::istrings
             method = FileIngestionMethod::Recursive;
             hashAlgo = string(hashAlgo, 2);
         }
-        const HashType hashType = parseHashType(hashAlgo);
+        const auto hashType = parseHashType(hashAlgo);
-
+        if (hash != "") {
-        return hash != ""
+            validatePath(pathS);
-            ? DerivationOutput {
+            return DerivationOutput {
                 .output = DerivationOutputCAFixed {
                     .hash = FixedOutputHash {
                         .method = std::move(method),
                         .hash = Hash::parseNonSRIUnprefixed(hash, hashType),
                     },
-                  }
+                },
-               }
+            };
-            : (settings.requireExperimentalFeature("ca-derivations"),
+        } else {
-              DerivationOutput {
+            settings.requireExperimentalFeature("ca-derivations");
+            assert(pathS == "");
+            return DerivationOutput {
                 .output = DerivationOutputCAFloating {
                     .method = std::move(method),
                     .hashType = std::move(hashType),
                 },
-              });
+            };
-    } else
+        }
+    } else {
+        validatePath(pathS);
         return DerivationOutput {
             .output = DerivationOutputInputAddressed {
-                .path = std::move(path),
+                .path = store.parseStorePath(pathS),
             }
         };
+    }
 }
 
 
@@ -316,17 +332,19 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
     for (auto & i : outputs) {
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
-        s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(i.second.path(store, name)));
         std::visit(overloaded {
             [&](DerivationOutputInputAddressed doi) {
+                s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(doi.path));
                 s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, "");
             },
             [&](DerivationOutputCAFixed dof) {
+                s += ','; printUnquotedString(s, maskOutputs ? "" : store.printStorePath(dof.path(store, name, i.first)));
                 s += ','; printUnquotedString(s, dof.hash.printMethodAlgo());
                 s += ','; printUnquotedString(s, dof.hash.hash.to_string(Base16, false));
             },
             [&](DerivationOutputCAFloating dof) {
+                s += ','; printUnquotedString(s, "");
                 s += ','; printUnquotedString(s, makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
                 s += ','; printUnquotedString(s, "");
             },
@@ -382,6 +400,16 @@ bool isDerivation(const string & fileName)
 }
 
 
+std::string outputPathName(std::string_view drvName, std::string_view outputName) {
+    std::string res { drvName };
+    if (outputName != "out") {
+        res += "-";
+        res += outputName;
+    }
+    return res;
+}
+
+
 DerivationType BasicDerivation::type() const
 {
     std::set<std::string_view> inputAddressedOutputs, fixedCAOutputs, floatingCAOutputs;
@@ -479,7 +507,7 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
             auto hash = hashString(htSHA256, "fixed:out:"
                 + dof.hash.printMethodAlgo() + ":"
                 + dof.hash.hash.to_string(Base16, false) + ":"
-                + store.printStorePath(i.second.path(store, drv.name)));
+                + store.printStorePath(dof.path(store, drv.name, i.first)));
             outputHashes.insert_or_assign(i.first, std::move(hash));
         }
         return outputHashes;
@@ -530,17 +558,9 @@ bool wantOutput(const string & output, const std::set<string> & wanted)
 }
 
 
-StorePathSet BasicDerivation::outputPaths(const Store & store) const
-{
-    StorePathSet paths;
-    for (auto & i : outputs)
-        paths.insert(i.second.path(store, name));
-    return paths;
-}
-
 static DerivationOutput readDerivationOutput(Source & in, const Store & store)
 {
-    auto path = store.parseStorePath(readString(in));
+    auto pathS = readString(in);
     auto hashAlgo = readString(in);
     auto hash = readString(in);
 
@@ -550,29 +570,35 @@ static DerivationOutput readDerivationOutput(Source & in, const Store & store)
             method = FileIngestionMethod::Recursive;
             hashAlgo = string(hashAlgo, 2);
         }
-        auto hashType = parseHashType(hashAlgo);
+        const auto hashType = parseHashType(hashAlgo);
-        return hash != ""
+        if (hash != "") {
-            ? DerivationOutput {
+            validatePath(pathS);
+            return DerivationOutput {
                 .output = DerivationOutputCAFixed {
                     .hash = FixedOutputHash {
                         .method = std::move(method),
                         .hash = Hash::parseNonSRIUnprefixed(hash, hashType),
                     },
-                  }
+                },
-               }
+            };
-            : (settings.requireExperimentalFeature("ca-derivations"),
+        } else {
-              DerivationOutput {
+            settings.requireExperimentalFeature("ca-derivations");
+            assert(pathS == "");
+            return DerivationOutput {
                 .output = DerivationOutputCAFloating {
                     .method = std::move(method),
                     .hashType = std::move(hashType),
                 },
-              });
+            };
-    } else
+        }
+    } else {
+        validatePath(pathS);
         return DerivationOutput {
             .output = DerivationOutputInputAddressed {
-                .path = std::move(path),
+                .path = store.parseStorePath(pathS),
             }
         };
+    }
 }
 
 StringSet BasicDerivation::outputNames() const
@@ -624,18 +650,21 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
 {
     out << drv.outputs.size();
     for (auto & i : drv.outputs) {
-        out << i.first
+        out << i.first;
-            << store.printStorePath(i.second.path(store, drv.name));
         std::visit(overloaded {
             [&](DerivationOutputInputAddressed doi) {
-                out << "" << "";
+                out << store.printStorePath(doi.path)
+                    << ""
+                    << "";
             },
             [&](DerivationOutputCAFixed dof) {
-                out << dof.hash.printMethodAlgo()
+                out << store.printStorePath(dof.path(store, drv.name, i.first))
+                    << dof.hash.printMethodAlgo()
                     << dof.hash.hash.to_string(Base16, false);
             },
             [&](DerivationOutputCAFloating dof) {
-                out << (makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType))
+                out << ""
+                    << (makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType))
                     << "";
             },
         }, i.second.output);
@@ -654,5 +683,14 @@ std::string hashPlaceholder(const std::string & outputName)
     return "/" + hashString(htSHA256, "nix-output:" + outputName).to_string(Base32, false);
 }
 
+StorePath downstreamPlaceholder(const Store & store, const StorePath & drvPath, std::string_view outputName)
+{
+    auto drvNameWithExtension = drvPath.name();
+    auto drvName = drvNameWithExtension.substr(0, drvNameWithExtension.size() - 4);
+    return store.makeStorePath(
+        "downstream-placeholder:" + std::string { drvPath.name() } + ":" + std::string { outputName },
+        "compressed:" + std::string { drvPath.hashPart() },
+        outputPathName(drvName, outputName));
+}
 
 }

src/libstore/derivations.hh

@@ -27,6 +27,7 @@ struct DerivationOutputInputAddressed
 struct DerivationOutputCAFixed
 {
     FixedOutputHash hash; /* hash used for expected hash computation */
+    StorePath path(const Store & store, std::string_view drvName, std::string_view outputName) const;
 };
 
 /* Floating-output derivations, whose output paths are content addressed, but
@@ -48,12 +49,6 @@ struct DerivationOutput
     > output;
     std::optional<HashType> hashAlgoOpt(const Store & store) const;
     std::optional<StorePath> pathOpt(const Store & store, std::string_view drvName) const;
-    /* DEPRECATED: Remove after CA drvs are fully implemented */
-    StorePath path(const Store & store, std::string_view drvName) const {
-        auto p = pathOpt(store, drvName);
-        if (!p) throw UnimplementedError("floating content-addressed derivations are not yet implemented");
-        return *p;
-    }
 };
 
 typedef std::map<string, DerivationOutput> DerivationOutputs;
@@ -101,9 +96,6 @@ struct BasicDerivation
     /* Return true iff this is a fixed-output derivation. */
     DerivationType type() const;
 
-    /* Return the output paths of a derivation. */
-    StorePathSet outputPaths(const Store & store) const;
-
     /* Return the output names of a derivation. */
     StringSet outputNames() const;
 
@@ -136,6 +128,8 @@ Derivation readDerivation(const Store & store, const Path & drvPath, std::string
 // FIXME: remove
 bool isDerivation(const string & fileName);
 
+std::string outputPathName(std::string_view drvName, std::string_view outputName);
+
 // known CA drv's output hashes, current just for fixed-output derivations
 // whose output hashes are always known since they are fixed up-front.
 typedef std::map<std::string, Hash> CaOutputHashes;
@@ -185,4 +179,6 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
 
 std::string hashPlaceholder(const std::string & outputName);
 
+StorePath downstreamPlaceholder(const Store & store, const StorePath & drvPath, std::string_view outputName);
+
 }

src/libstore/local-store.cc

@@ -578,13 +578,32 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
                 envHasRightPath(path, i.first);
             },
             [&](DerivationOutputCAFloating _) {
-                throw UnimplementedError("floating CA output derivations are not yet implemented");
+                /* Nothing to check */
             },
         }, i.second.output);
     }
 }
 
 
+void LocalStore::linkDeriverToPath(const StorePath & deriver, const string & outputName, const StorePath & output)
+{
+    auto state(_state.lock());
+    return linkDeriverToPath(*state, queryValidPathId(*state, deriver), outputName, output);
+}
+
+void LocalStore::linkDeriverToPath(State & state, uint64_t deriver, const string & outputName, const StorePath & output)
+{
+    retrySQLite<void>([&]() {
+        state.stmtAddDerivationOutput.use()
+            (deriver)
+            (outputName)
+            (printStorePath(output))
+            .exec();
+    });
+
+}
+
+
 uint64_t LocalStore::addValidPath(State & state,
     const ValidPathInfo & info, bool checkOutputs)
 {
@@ -619,11 +638,11 @@ uint64_t LocalStore::addValidPath(State & state,
         if (checkOutputs) checkDerivationOutputs(info.path, drv);
 
         for (auto & i : drv.outputs) {
-            state.stmtAddDerivationOutput.use()
+            /* Floating CA derivations have indeterminate output paths until
-                (id)
+               they are built, so don't register anything in that case */
-                (i.first)
+            auto optPath = i.second.pathOpt(*this, drv.name);
-                (printStorePath(i.second.path(*this, drv.name)))
+            if (optPath)
-                .exec();
+                linkDeriverToPath(state, id, i.first, *optPath);
         }
     }
 

src/libstore/local-store.hh

@@ -282,6 +282,12 @@ private:
        specified by the ‘secret-key-files’ option. */
     void signPathInfo(ValidPathInfo & info);
 
+    /* Add a mapping from the deriver of the path info (if specified) to its
+     * out path
+     */
+    void linkDeriverToPath(const StorePath & deriver, const string & outputName, const StorePath & output);
+    void linkDeriverToPath(State & state, uint64_t deriver, const string & outputName, const StorePath & output);
+
     Path getRealStoreDir() override { return realStoreDir; }
 
     void createUser(const std::string & userName, uid_t userId) override;

src/libstore/misc.cc

@@ -203,17 +203,24 @@ void Store::queryMissing(const std::vector<StorePathWithOutputs> & targets,
                 return;
             }
 
+            PathSet invalid;
+            /* true for regular derivations, and CA derivations for which we
+               have a trust mapping for all wanted outputs. */
+            auto knownOutputPaths = true;
+            for (auto & [outputName, pathOpt] : queryDerivationOutputMap(path.path)) {
+                if (!pathOpt) {
+                    knownOutputPaths = false;
+                    break;
+                }
+                if (wantOutput(outputName, path.outputs) && !isValidPath(*pathOpt))
+                    invalid.insert(printStorePath(*pathOpt));
+            }
+            if (knownOutputPaths && invalid.empty()) return;
+
             auto drv = make_ref<Derivation>(derivationFromPath(path.path));
             ParsedDerivation parsedDrv(StorePath(path.path), *drv);
 
-            PathSet invalid;
+            if (knownOutputPaths && settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
-            for (auto & j : drv->outputs)
-                if (wantOutput(j.first, path.outputs)
-                    && !isValidPath(j.second.path(*this, drv->name)))
-                    invalid.insert(printStorePath(j.second.path(*this, drv->name)));
-            if (invalid.empty()) return;
-
-            if (settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
                 auto drvState = make_ref<Sync<DrvState>>(DrvState(invalid.size()));
                 for (auto & output : invalid)
                     pool.enqueue(std::bind(checkOutput, printStorePath(path.path), drv, output, drvState));

src/libstore/references.cc

@@ -79,9 +79,17 @@ void RefScanSink::operator () (const unsigned char * data, size_t len)
 std::pair<PathSet, HashResult> scanForReferences(const string & path,
     const PathSet & refs)
 {
-    RefScanSink refsSink;
     HashSink hashSink { htSHA256 };
-    TeeSink sink { refsSink, hashSink };
+    auto found = scanForReferences(hashSink, path, refs);
+    auto hash = hashSink.finish();
+    return std::pair<PathSet, HashResult>(found, hash);
+}
+
+PathSet scanForReferences(Sink & toTee,
+    const string & path, const PathSet & refs)
+{
+    RefScanSink refsSink;
+    TeeSink sink { refsSink, toTee };
     std::map<string, Path> backMap;
 
     /* For efficiency (and a higher hit rate), just search for the
@@ -111,9 +119,7 @@ std::pair<PathSet, HashResult> scanForReferences(const string & path,
         found.insert(j->second);
     }
 
-    auto hash = hashSink.finish();
+    return found;
-
-    return std::pair<PathSet, HashResult>(found, hash);
 }
 
 

src/libstore/references.hh

@@ -7,6 +7,8 @@ namespace nix {
 
 std::pair<PathSet, HashResult> scanForReferences(const Path & path, const PathSet & refs);
 
+PathSet scanForReferences(Sink & toTee, const Path & path, const PathSet & refs);
+
 struct RewritingSink : Sink
 {
     std::string from, to, prev;

src/libstore/store-api.cc

@@ -140,21 +140,28 @@ StorePathWithOutputs Store::followLinksToStorePathWithOutputs(std::string_view p
 */
 
 
-StorePath Store::makeStorePath(const string & type,
+StorePath Store::makeStorePath(std::string_view type,
-    const Hash & hash, std::string_view name) const
+    std::string_view hash, std::string_view name) const
 {
     /* e.g., "source:sha256:1abc...:/nix/store:foo.tar.gz" */
-    string s = type + ":" + hash.to_string(Base16, true) + ":" + storeDir + ":" + std::string(name);
+    string s = std::string { type } + ":" + std::string { hash }
+        + ":" + storeDir + ":" + std::string { name };
     auto h = compressHash(hashString(htSHA256, s), 20);
     return StorePath(h, name);
 }
 
 
-StorePath Store::makeOutputPath(const string & id,
+StorePath Store::makeStorePath(std::string_view type,
     const Hash & hash, std::string_view name) const
 {
-    return makeStorePath("output:" + id, hash,
+    return makeStorePath(type, hash.to_string(Base16, true), name);
-        std::string(name) + (id == "out" ? "" : "-" + id));
+}
+
+
+StorePath Store::makeOutputPath(std::string_view id,
+    const Hash & hash, std::string_view name) const
+{
+    return makeStorePath("output:" + std::string { id }, hash, outputPathName(name, id));
 }
 
 

src/libstore/store-api.hh

@@ -244,10 +244,12 @@ public:
     StorePathWithOutputs followLinksToStorePathWithOutputs(std::string_view path) const;
 
     /* Constructs a unique store path name. */
-    StorePath makeStorePath(const string & type,
+    StorePath makeStorePath(std::string_view type,
+        std::string_view hash, std::string_view name) const;
+    StorePath makeStorePath(std::string_view type,
         const Hash & hash, std::string_view name) const;
 
-    StorePath makeOutputPath(const string & id,
+    StorePath makeOutputPath(std::string_view id,
         const Hash & hash, std::string_view name) const;
 
     StorePath makeFixedOutputPath(FileIngestionMethod method,

src/libutil/serialise.hh

@@ -22,6 +22,12 @@ struct Sink
     }
 };
 
+/* Just throws away data. */
+struct NullSink : Sink
+{
+    void operator () (const unsigned char * data, size_t len) override
+    { }
+};
 
 /* A buffered abstract sink. */
 struct BufferedSink : virtual Sink

src/nix-build/nix-build.cc

@@ -487,50 +487,56 @@ static void _main(int argc, char * * argv)
 
         std::vector<StorePathWithOutputs> pathsToBuild;
 
-        std::map<Path, Path> drvPrefixes;
+        std::map<StorePath, std::pair<size_t, StringSet>> drvMap;
-        std::map<Path, Path> resultSymlinks;
-        std::vector<Path> outPaths;
 
         for (auto & drvInfo : drvs) {
-            auto drvPath = drvInfo.queryDrvPath();
+            auto drvPath = store->parseStorePath(drvInfo.queryDrvPath());
-            auto outPath = drvInfo.queryOutPath();
 
             auto outputName = drvInfo.queryOutputName();
             if (outputName == "")
-                throw Error("derivation '%s' lacks an 'outputName' attribute", drvPath);
+                throw Error("derivation '%s' lacks an 'outputName' attribute", store->printStorePath(drvPath));
 
-            pathsToBuild.push_back({store->parseStorePath(drvPath), {outputName}});
+            pathsToBuild.push_back({drvPath, {outputName}});
 
-            std::string drvPrefix;
+            auto i = drvMap.find(drvPath);
-            auto i = drvPrefixes.find(drvPath);
+            if (i != drvMap.end())
-            if (i != drvPrefixes.end())
+                i->second.second.insert(outputName);
-                drvPrefix = i->second;
             else {
-                drvPrefix = outLink;
+                drvMap[drvPath] = {drvMap.size(), {outputName}};
-                if (drvPrefixes.size())
-                    drvPrefix += fmt("-%d", drvPrefixes.size() + 1);
-                drvPrefixes[drvPath] = drvPrefix;
             }
-
-            std::string symlink = drvPrefix;
-            if (outputName != "out") symlink += "-" + outputName;
-
-            resultSymlinks[symlink] = outPath;
-            outPaths.push_back(outPath);
         }
 
         buildPaths(pathsToBuild);
 
         if (dryRun) return;
 
-        for (auto & symlink : resultSymlinks)
+        std::vector<StorePath> outPaths;
-            if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>())
+
-                store2->addPermRoot(store->parseStorePath(symlink.second), absPath(symlink.first), true);
+        for (auto & [drvPath, info] : drvMap) {
+            auto & [counter, wantedOutputs] = info;
+            std::string drvPrefix = outLink;
+            if (counter)
+                drvPrefix += fmt("-%d", counter + 1);
+
+            auto builtOutputs = store->queryDerivationOutputMapAssumeTotal(drvPath);
+
+            for (auto & outputName : wantedOutputs) {
+                auto outputPath = builtOutputs.at(outputName);
+
+                if (auto store2 = store.dynamic_pointer_cast<LocalFSStore>()) {
+                    std::string symlink = drvPrefix;
+                    if (outputName != "out") symlink += "-" + outputName;
+                    store2->addPermRoot(outputPath, absPath(symlink), true);
+                }
+
+                outPaths.push_back(outputPath);
+            }
+        }
 
         logger->stop();
 
         for (auto & path : outPaths)
-            std::cout << path << '\n';
+            std::cout << store->printStorePath(path) << '\n';
     }
 }
 

src/nix-store/nix-store.cc

@@ -65,6 +65,7 @@ static PathSet realisePath(StorePathWithOutputs path, bool build = true)
 
     if (path.path.isDerivation()) {
         if (build) store->buildPaths({path});
+        auto outputPaths = store->queryDerivationOutputMapAssumeTotal(path.path);
         Derivation drv = store->derivationFromPath(path.path);
         rootNr++;
 
@@ -77,7 +78,8 @@ static PathSet realisePath(StorePathWithOutputs path, bool build = true)
             if (i == drv.outputs.end())
                 throw Error("derivation '%s' does not have an output named '%s'",
                     store2->printStorePath(path.path), j);
-            auto outPath = store2->printStorePath(i->second.path(*store, drv.name));
+            auto outPath = outputPaths.at(i->first);
+            auto retPath = store->printStorePath(outPath);
             if (store2) {
                 if (gcRoot == "")
                     printGCWarning();
@@ -85,10 +87,10 @@ static PathSet realisePath(StorePathWithOutputs path, bool build = true)
                     Path rootName = gcRoot;
                     if (rootNr > 1) rootName += "-" + std::to_string(rootNr);
                     if (i->first != "out") rootName += "-" + i->first;
-                    outPath = store2->addPermRoot(store->parseStorePath(outPath), rootName, indirectRoot);
+                    retPath = store2->addPermRoot(outPath, rootName, indirectRoot);
                 }
             }
-            outputs.insert(outPath);
+            outputs.insert(retPath);
         }
         return outputs;
     }
@@ -218,8 +220,14 @@ static StorePathSet maybeUseOutputs(const StorePath & storePath, bool useOutput,
     if (useOutput && storePath.isDerivation()) {
         auto drv = store->derivationFromPath(storePath);
         StorePathSet outputs;
-        for (auto & i : drv.outputs)
+        if (forceRealise)
-            outputs.insert(i.second.path(*store, drv.name));
+            return store->queryDerivationOutputs(storePath);
+        for (auto & i : drv.outputs) {
+            auto optPath = i.second.pathOpt(*store, drv.name);
+            if (!optPath)
+                throw UsageError("Cannot use output path of floating content-addressed derivation until we know what it is (e.g. by building it)");
+            outputs.insert(*optPath);
+        }
         return outputs;
     }
     else return {storePath};
@@ -309,11 +317,9 @@ static void opQuery(Strings opFlags, Strings opArgs)
 
         case qOutputs: {
             for (auto & i : opArgs) {
-                auto i2 = store->followLinksToStorePath(i);
+                auto outputs = maybeUseOutputs(store->followLinksToStorePath(i), true, forceRealise);
-                if (forceRealise) realisePath({i2});
+                for (auto & outputPath : outputs)
-                Derivation drv = store->derivationFromPath(i2);
+                    cout << fmt("%1%\n", store->printStorePath(outputPath));
-                for (auto & j : drv.outputs)
-                    cout << fmt("%1%\n", store->printStorePath(j.second.path(*store, drv.name)));
             }
             break;
         }

src/nix/build.cc

@@ -74,7 +74,8 @@ struct CmdBuild : InstallablesCommand, MixDryRun, MixProfile
                             store2->addPermRoot(bo.path, absPath(symlink), true);
                         },
                         [&](BuildableFromDrv bfd) {
-                            for (auto & output : bfd.outputs) {
+                            auto builtOutputs = store->queryDerivationOutputMapAssumeTotal(bfd.drvPath);
+                            for (auto & output : builtOutputs) {
                                 std::string symlink = outLink;
                                 if (i) symlink += fmt("-%d", i);
                                 if (output.first != "out") symlink += fmt("-%s", output.first);

src/nix/command.cc

@@ -137,7 +137,9 @@ void MixProfile::updateProfile(const Buildables & buildables)
             },
             [&](BuildableFromDrv bfd) {
                 for (auto & output : bfd.outputs) {
-                    result.push_back(output.second);
+                    if (!output.second)
+                        throw Error("output path should be known because we just tried to build it");
+                    result.push_back(*output.second);
                 }
             },
         }, buildable);

src/nix/installables.cc

@@ -302,10 +302,10 @@ struct InstallableStorePath : Installable
     Buildables toBuildables() override
     {
         if (storePath.isDerivation()) {
-            std::map<std::string, StorePath> outputs;
+            std::map<std::string, std::optional<StorePath>> outputs;
             auto drv = store->readDerivation(storePath);
             for (auto & [name, output] : drv.outputs)
-                outputs.emplace(name, output.path(*store, drv.name));
+                outputs.emplace(name, output.pathOpt(*store, drv.name));
             return {
                 BuildableFromDrv {
                     .drvPath = storePath,
@@ -331,7 +331,7 @@ Buildables InstallableValue::toBuildables()
 {
     Buildables res;
 
-    std::map<StorePath, OutputPathMap> drvsToOutputs;
+    std::map<StorePath, std::map<std::string, std::optional<StorePath>>> drvsToOutputs;
 
     // Group by derivation, helps with .all in particular
     for (auto & drv : toDerivations()) {
@@ -674,8 +674,11 @@ StorePathSet toStorePaths(ref<Store> store,
                     outPaths.insert(bo.path);
                 },
                 [&](BuildableFromDrv bfd) {
-                    for (auto & output : bfd.outputs)
+                    for (auto & output : bfd.outputs) {
-                        outPaths.insert(output.second);
+                        if (!output.second)
+                            throw Error("Cannot operate on output of unbuilt CA drv");
+                        outPaths.insert(*output.second);
+                    }
                 },
             }, b);
     } else {

src/nix/installables.hh

@@ -20,7 +20,7 @@ struct BuildableOpaque {
 
 struct BuildableFromDrv {
     StorePath drvPath;
-    std::map<std::string, StorePath> outputs;
+    std::map<std::string, std::optional<StorePath>> outputs;
 };
 
 typedef std::variant<
@@ -82,7 +82,7 @@ struct InstallableValue : Installable
     struct DerivationInfo
     {
         StorePath drvPath;
-        StorePath outPath;
+        std::optional<StorePath> outPath;
         std::string outputName;
     };
 

src/nix/profile.cc

@@ -178,7 +178,9 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
                 auto [attrPath, resolvedRef, drv] = installable2->toDerivation();
 
                 ProfileElement element;
-                element.storePaths = {drv.outPath}; // FIXME
+                if (!drv.outPath)
+                    throw UnimplementedError("CA derivations are not yet supported by 'nix profile'");
+                element.storePaths = {*drv.outPath}; // FIXME
                 element.source = ProfileElementSource{
                     installable2->flakeRef,
                     resolvedRef,
@@ -189,7 +191,7 @@ struct CmdProfileInstall : InstallablesCommand, MixDefaultProfile
 
                 manifest.elements.emplace_back(std::move(element));
             } else
-                throw Error("'nix profile install' does not support argument '%s'", installable->what());
+                throw UnimplementedError("'nix profile install' does not support argument '%s'", installable->what());
         }
 
         store->buildPaths(pathsToBuild);
@@ -347,7 +349,9 @@ struct CmdProfileUpgrade : virtual SourceExprCommand, MixDefaultProfile, MixProf
                 printInfo("upgrading '%s' from flake '%s' to '%s'",
                     element.source->attrPath, element.source->resolvedRef, resolvedRef);
 
-                element.storePaths = {drv.outPath}; // FIXME
+                if (!drv.outPath)
+                    throw UnimplementedError("CA derivations are not yet supported by 'nix profile'");
+                element.storePaths = {*drv.outPath}; // FIXME
                 element.source = ProfileElementSource{
                     installable.flakeRef,
                     resolvedRef,

src/nix/repl.cc

@@ -488,10 +488,10 @@ bool NixRepl::processLine(string line)
                but doing it in a child makes it easier to recover from
                problems / SIGINT. */
             if (runProgram(settings.nixBinDir + "/nix", Strings{"build", "--no-link", drvPath}) == 0) {
-                auto drv = readDerivation(*state->store, drvPath, Derivation::nameFromPath(state->store->parseStorePath(drvPath)));
+                auto outputs = state->store->queryDerivationOutputMapAssumeTotal(state->store->parseStorePath(drvPath));
                 std::cout << std::endl << "this derivation produced the following outputs:" << std::endl;
-                for (auto & i : drv.outputs)
+                for (auto & i : outputs)
-                    std::cout << fmt("  %s -> %s\n", i.first, state->store->printStorePath(i.second.path(*state->store, drv.name)));
+                    std::cout << fmt("  %s -> %s\n", i.first, state->store->printStorePath(i.second));
             }
         } else if (command == ":i") {
             runProgram(settings.nixBinDir + "/nix-env", Strings{"-i", drvPath});

src/nix/show-derivation.cc

@@ -69,12 +69,12 @@ struct CmdShowDerivation : InstallablesCommand
                 auto outputsObj(drvObj.object("outputs"));
                 for (auto & output : drv.outputs) {
                     auto outputObj(outputsObj.object(output.first));
-                    outputObj.attr("path", store->printStorePath(output.second.path(*store, drv.name)));
-
                     std::visit(overloaded {
                         [&](DerivationOutputInputAddressed doi) {
+                            outputObj.attr("path", store->printStorePath(doi.path));
                         },
                         [&](DerivationOutputCAFixed dof) {
+                            outputObj.attr("path", store->printStorePath(dof.path(*store, drv.name, output.first)));
                             outputObj.attr("hashAlgo", dof.hash.printMethodAlgo());
                             outputObj.attr("hash", dof.hash.hash.to_string(Base16, false));
                         },

tests/content-addressed.nix

@@ -0,0 +1,19 @@
+with import ./config.nix;
+
+{ seed ? 0 }:
+# A simple content-addressed derivation.
+# The derivation can be arbitrarily modified by passing a different `seed`,
+# but the output will always be the same
+mkDerivation {
+  name = "simple-content-addressed";
+  buildCommand = ''
+    set -x
+    echo "Building a CA derivation"
+    echo "The seed is ${toString seed}"
+    mkdir -p $out
+    echo "Hello World" > $out/hello
+  '';
+  __contentAddressed = true;
+  outputHashMode = "recursive";
+  outputHashAlgo = "sha256";
+}

tests/content-addressed.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+clearStore
+clearCache
+
+export REMOTE_STORE=file://$cacheDir
+
+drv=$(nix-instantiate --experimental-features ca-derivations ./content-addressed.nix --arg seed 1)
+nix --experimental-features 'nix-command ca-derivations' show-derivation --derivation "$drv" --arg seed 1
+
+out1=$(nix-build --experimental-features ca-derivations ./content-addressed.nix --arg seed 1 --no-out-link)
+out2=$(nix-build --experimental-features ca-derivations ./content-addressed.nix --arg seed 2 --no-out-link)
+
+test $out1 == $out2

tests/local.mk

@@ -32,7 +32,8 @@ nix_tests = \
   post-hook.sh \
   function-trace.sh \
   recursive.sh \
-  flakes.sh
+  flakes.sh \
+  content-addressed.sh
   # parallel.sh
 
 install-tests += $(foreach x, $(nix_tests), tests/$(x))

tests/multiple-outputs.nix

@@ -2,6 +2,21 @@ with import ./config.nix;
 
 rec {
 
+  # Want to ensure that "out" doesn't get a suffix on it's path.
+  nameCheck = mkDerivation {
+    name = "multiple-outputs-a";
+    outputs = [ "out" "dev" ];
+    builder = builtins.toFile "builder.sh"
+      ''
+        mkdir $first $second
+        test -z $all
+        echo "first" > $first/file
+        echo "second" > $second/file
+        ln -s $first $second/link
+      '';
+    helloString = "Hello, world!";
+  };
+
   a = mkDerivation {
     name = "multiple-outputs-a";
     outputs = [ "first" "second" ];

tests/multiple-outputs.sh

@@ -4,6 +4,12 @@ clearStore
 
 rm -f $TEST_ROOT/result*
 
+# Test whether the output names match our expectations
+outPath=$(nix-instantiate multiple-outputs.nix --eval -A nameCheck.out.outPath)
+[ "$(echo "$outPath" | sed -E 's_^".*/[^-/]*-([^/]*)"$_\1_')" = "multiple-outputs-a" ]
+outPath=$(nix-instantiate multiple-outputs.nix --eval -A nameCheck.dev.outPath)
+[ "$(echo "$outPath" | sed -E 's_^".*/[^-/]*-([^/]*)"$_\1_')" = "multiple-outputs-a-dev" ]
+
 # Test whether read-only evaluation works when referring to the
 # ‘drvPath’ attribute.
 echo "evaluating c..."