Derivations can output "text-hashed" data

In particular, this means that derivations can output derivations. But
that ramification isn't (yet!) useful as we would want, since there is
no way to have a dependent derivation that is itself a dependent
derivation.

src/libexpr/primops.cc

@@ -851,7 +851,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
     bool contentAddressed = false;
     std::optional<std::string> outputHash;
     std::string outputHashAlgo;
-    auto ingestionMethod = FileIngestionMethod::Flat;
+    ContentAddressMethod ingestionMethod = FileIngestionMethod::Flat;
 
     StringSet outputs;
     outputs.insert("out");
@@ -864,6 +864,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         auto handleHashMode = [&](const std::string & s) {
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
+            else if (s == "text") ingestionMethod = TextHashMethod {};
             else
                 throw EvalError({
                     .hint = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
@@ -995,8 +996,11 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             state.store->computeFSClosure(state.store->parseStorePath(std::string_view(path).substr(1)), refs);
             for (auto & j : refs) {
                 drv.inputSrcs.insert(j);
-                if (j.isDerivation())
-                    drv.inputDrvs[j] = state.store->readDerivation(j).outputNames();
+                if (j.isDerivation()) {
+                    Derivation jDrv = state.store->readDerivation(j);
+                    if(jDrv.type() != DerivationType::CAFloating)
+                        drv.inputDrvs[j] = jDrv.outputNames();
+                }
             }
         }
 
@@ -1025,9 +1029,9 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         });
 
     /* Check whether the derivation name is valid. */
-    if (isDerivation(drvName))
+    if (isDerivation(drvName) && ingestionMethod != ContentAddressMethod { TextHashMethod { } })
         throw EvalError({
-            .hint = hintfmt("derivation names are not allowed to end in '%s'", drvExtension),
+            .hint = hintfmt("derivation names are allowed to end in '%s' only if they produce a single derivation file", drvExtension),
             .errPos = posDrvName
         });
 
@@ -1045,22 +1049,16 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
         std::optional<HashType> ht = parseHashTypeOpt(outputHashAlgo);
         Hash h = newHashAllowEmpty(*outputHash, ht);
 
-        auto outPath = state.store->makeFixedOutputPath(drvName, FixedOutputInfo {
-            {
-                .method = ingestionMethod,
-                .hash = h,
-            },
-            {},
-        });
-        drv.env["out"] = state.store->printStorePath(outPath);
-        drv.outputs.insert_or_assign("out", DerivationOutput {
-                .output = DerivationOutputCAFixed {
-                    .hash = FixedOutputHash {
-                        .method = ingestionMethod,
-                        .hash = std::move(h),
-                    },
-                },
-        });
+        // FIXME non-trivial fixed refs set
+        auto ca = contentAddressFromMethodHashAndRefs(
+            ingestionMethod,
+            std::move(h),
+            {});
+
+        DerivationOutputCAFixed dof { .ca = ca };
+
+        drv.env["out"] = state.store->printStorePath(dof.path(*state.store, drvName, "out"));
+        drv.outputs.insert_or_assign("out", DerivationOutput { .output = dof });
     }
 
     else if (contentAddressed) {

src/libstore/build.cc

@@ -4070,26 +4070,35 @@ void DerivationGoal::registerOutputs()
 
         auto newInfoFromCA = [&](const DerivationOutputCAFloating outputHash) -> ValidPathInfo {
             auto & st = outputStats.at(outputName);
-            if (outputHash.method == FileIngestionMethod::Flat) {
+            if (outputHash.method == ContentAddressMethod { FileIngestionMethod::Flat } ||
+                outputHash.method == ContentAddressMethod { TextHashMethod {} })
+            {
                 /* The output path should be a regular file without execute permission. */
                 if (!S_ISREG(st.st_mode) || (st.st_mode & S_IXUSR) != 0)
                     throw BuildError(
                         "output path '%1%' should be a non-executable regular file "
-                        "since recursive hashing is not enabled (outputHashMode=flat)",
+                        "since recursive hashing is not enabled (one of outputHashMode={flat,text} is true)",
                         actualPath);
             }
             rewriteOutput();
             /* FIXME optimize and deduplicate with addToStore */
             std::string oldHashPart { scratchPath.hashPart() };
             HashModuloSink caSink { outputHash.hashType, oldHashPart };
-            switch (outputHash.method) {
-            case FileIngestionMethod::Recursive:
-                dumpPath(actualPath, caSink);
-                break;
-            case FileIngestionMethod::Flat:
-                readFile(actualPath, caSink);
-                break;
-            }
+            std::visit(overloaded {
+                [&](TextHashMethod _) {
+                    readFile(actualPath, caSink);
+                },
+                [&](FileIngestionMethod m2) {
+                    switch (m2) {
+                    case FileIngestionMethod::Recursive:
+                        dumpPath(actualPath, caSink);
+                        break;
+                    case FileIngestionMethod::Flat:
+                        readFile(actualPath, caSink);
+                        break;
+                    }
+                },
+            }, outputHash.method);
             auto got = caSink.finish().first;
             HashModuloSink narSink { htSHA256, oldHashPart };
             dumpPath(actualPath, narSink);
@@ -4098,13 +4107,10 @@ void DerivationGoal::registerOutputs()
                 worker.store,
                 {
                     .name = outputPathName(drv->name, outputName),
-                    .info = FixedOutputInfo {
-                        {
-                            .method = outputHash.method,
-                            .hash = got,
-                        },
-                        rewriteRefs(),
-                    },
+                    .info = contentAddressFromMethodHashAndRefs(
+                        outputHash.method,
+                        std::move(got),
+                        rewriteRefs()),
                 },
                 narHashAndSize.first,
             };
@@ -4132,13 +4138,14 @@ void DerivationGoal::registerOutputs()
                 return newInfo0;
             },
             [&](DerivationOutputCAFixed dof) {
+                auto wanted = getContentAddressHash(dof.ca);
+
                 auto newInfo0 = newInfoFromCA(DerivationOutputCAFloating {
-                    .method = dof.hash.method,
-                    .hashType = dof.hash.hash.type,
+                    .method = getContentAddressMethod(dof.ca),
+                    .hashType = wanted.type,
                 });
 
                 /* Check wanted hash */
-                Hash & wanted = dof.hash.hash;
                 assert(newInfo0.ca);
                 auto got = getContentAddressHash(*newInfo0.ca);
                 if (wanted != got) {
@@ -4151,6 +4158,11 @@ void DerivationGoal::registerOutputs()
                             wanted.to_string(SRI, true),
                             got.to_string(SRI, true)));
                 }
+                if (static_cast<const PathReferences<StorePath> &>(newInfo0) != PathReferences<StorePath> {})
+                    delayedException = std::make_exception_ptr(
+                        BuildError("illegal path references in fixed-output derivation '%s'",
+                            worker.store.printStorePath(drvPath)));
+
                 return newInfo0;
             },
             [&](DerivationOutputCAFloating dof) {

src/libstore/content-address.cc

@@ -10,7 +10,7 @@ std::string FixedOutputHash::printMethodAlgo() const
 }
 
 
-std::string makeFileIngestionPrefix(const FileIngestionMethod m)
+std::string makeFileIngestionPrefix(FileIngestionMethod m)
 {
     switch (m) {
     case FileIngestionMethod::Flat:
@@ -21,6 +21,27 @@ std::string makeFileIngestionPrefix(const FileIngestionMethod m)
     assert(false);
 }
 
+std::string makeContentAddressingPrefix(ContentAddressMethod m) {
+    return std::visit(overloaded {
+        [](TextHashMethod _) -> std::string { return "text:"; },
+        [](FileIngestionMethod m2) {
+             /* Not prefixed for back compat with things that couldn't produce text before. */
+            return makeFileIngestionPrefix(m2);
+        },
+    }, m);
+}
+
+ContentAddressMethod parseContentAddressingPrefix(std::string_view & m)
+{
+    ContentAddressMethod method = FileIngestionMethod::Flat;
+    if (splitPrefix(m, "r:"))
+        method = FileIngestionMethod::Recursive;
+    else if (splitPrefix(m, "text:"))
+        method = TextHashMethod {};
+    return method;
+}
+
+
 std::string makeFixedOutputCA(FileIngestionMethod method, const Hash & hash)
 {
     return "fixed:"
@@ -43,14 +64,14 @@ std::string renderContentAddress(ContentAddress ca)
     }, ca);
 }
 
-std::string renderContentAddressMethod(ContentAddressMethod cam)
+std::string renderContentAddressMethodAndHash(ContentAddressMethod cam, HashType ht)
 {
     return std::visit(overloaded {
-        [](TextHashMethod &th) {
-            return std::string{"text:"} + printHashType(htSHA256);
+        [&](TextHashMethod & th) {
+            return std::string{"text:"} + printHashType(ht);
         },
-        [](FixedOutputHashMethod &fshm) {
-            return "fixed:" + makeFileIngestionPrefix(fshm.fileIngestionMethod) + printHashType(fshm.hashType);
+        [&](FileIngestionMethod & fim) {
+            return "fixed:" + makeFileIngestionPrefix(fim) + printHashType(ht);
         }
     }, cam);
 }
@@ -58,7 +79,7 @@ std::string renderContentAddressMethod(ContentAddressMethod cam)
 /*
   Parses content address strings up to the hash.
  */
-static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & rest)
+static std::pair<ContentAddressMethod, HashType> parseContentAddressMethodPrefix(std::string_view & rest)
 {
     std::string_view wholeInput { rest };
 
@@ -82,19 +103,19 @@ static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & r
     if (prefix == "text") {
         // No parsing of the ingestion method, "text" only support flat.
         HashType hashType = parseHashType_();
-        if (hashType != htSHA256)
-            throw Error("text content address hash should use %s, but instead uses %s",
-                printHashType(htSHA256), printHashType(hashType));
-        return TextHashMethod {};
+        return {
+            TextHashMethod {},
+            std::move(hashType),
+        };
     } else if (prefix == "fixed") {
         // Parse method
         auto method = FileIngestionMethod::Flat;
         if (splitPrefix(rest, "r:"))
             method = FileIngestionMethod::Recursive;
         HashType hashType = parseHashType_();
-        return FixedOutputHashMethod {
-            .fileIngestionMethod = method,
-            .hashType = std::move(hashType),
+        return {
+            std::move(method),
+            std::move(hashType),
         };
     } else
         throw UsageError("content address prefix '%s' is unrecognized. Recogonized prefixes are 'text' or 'fixed'", prefix);
@@ -103,25 +124,24 @@ static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & r
 ContentAddress parseContentAddress(std::string_view rawCa) {
     auto rest = rawCa;
 
-    ContentAddressMethod caMethod = parseContentAddressMethodPrefix(rest);
+    auto [caMethod, hashType] = parseContentAddressMethodPrefix(rest);
 
-    return std::visit(
-        overloaded {
-            [&](TextHashMethod thm) {
-                return ContentAddress(TextHash {
-                    .hash = Hash::parseNonSRIUnprefixed(rest, htSHA256)
-                });
-            },
-            [&](FixedOutputHashMethod fohMethod) {
-                return ContentAddress(FixedOutputHash {
-                    .method = fohMethod.fileIngestionMethod,
-                    .hash = Hash::parseNonSRIUnprefixed(rest, std::move(fohMethod.hashType)),
-                });
-            },
-        }, caMethod);
+    return std::visit(overloaded {
+        [&](TextHashMethod _) {
+            return ContentAddress(TextHash {
+                .hash = Hash::parseNonSRIUnprefixed(rest, hashType)
+            });
+        },
+        [&](FileIngestionMethod fim) {
+            return ContentAddress(FixedOutputHash {
+                .method = fim,
+                .hash = Hash::parseNonSRIUnprefixed(rest, hashType),
+            });
+        },
+    }, caMethod);
 }
 
-ContentAddressMethod parseContentAddressMethod(std::string_view caMethod)
+std::pair<ContentAddressMethod, HashType> parseContentAddressMethod(std::string_view caMethod)
 {
     std::string_view asPrefix {std::string{caMethod} + ":"};
     return parseContentAddressMethodPrefix(asPrefix);
@@ -137,6 +157,42 @@ std::string renderContentAddress(std::optional<ContentAddress> ca)
     return ca ? renderContentAddress(*ca) : "";
 }
 
+ContentAddressWithReferences contentAddressFromMethodHashAndRefs(
+    ContentAddressMethod method, Hash && hash, PathReferences<StorePath> && refs)
+{
+    return std::visit(overloaded {
+        [&](TextHashMethod _) -> ContentAddressWithReferences {
+            if (refs.hasSelfReference)
+                throw UsageError("Cannot have a self reference with text hashing scheme");
+            return TextInfo {
+                { .hash = std::move(hash) },
+                std::move(refs.references),
+            };
+        },
+        [&](FileIngestionMethod m2) -> ContentAddressWithReferences {
+            return FixedOutputInfo {
+                {
+                    .method = m2,
+                    .hash = std::move(hash),
+                },
+                std::move(refs),
+            };
+        },
+    }, method);
+}
+
+ContentAddressMethod getContentAddressMethod(const ContentAddressWithReferences & ca)
+{
+    return std::visit(overloaded {
+        [](TextInfo th) -> ContentAddressMethod {
+            return TextHashMethod {};
+        },
+        [](FixedOutputInfo fsh) -> ContentAddressMethod {
+            return fsh.method;
+        },
+    }, ca);
+}
+
 Hash getContentAddressHash(const ContentAddress & ca)
 {
     return std::visit(overloaded {
@@ -160,4 +216,21 @@ ContentAddressWithReferences caWithoutRefs(const ContentAddress & ca) {
     }, ca);
 }
 
+Hash getContentAddressHash(const ContentAddressWithReferences & ca)
+{
+    return std::visit(overloaded {
+        [](TextInfo th) {
+            return th.hash;
+        },
+        [](FixedOutputInfo fsh) {
+            return fsh.hash;
+        },
+    }, ca);
+}
+
+std::string printMethodAlgo(const ContentAddressWithReferences & ca) {
+    return makeContentAddressingPrefix(getContentAddressMethod(ca))
+        + printHashType(getContentAddressHash(ca).type);
+}
+
 }

src/libstore/content-address.hh

@@ -10,11 +10,45 @@ namespace nix {
  * Mini content address
  */
 
+/* We only have one way to hash text with references, so this is a single-value
+   type, mainly useful with std::variant.
+*/
+struct TextHashMethod : std::monostate { };
+
 enum struct FileIngestionMethod : uint8_t {
     Flat = false,
     Recursive = true
 };
 
+/* Compute the prefix to the hash algorithm which indicates how the files were
+   ingested. */
+std::string makeFileIngestionPrefix(FileIngestionMethod m);
+
+
+/* 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. */
+typedef std::variant<
+    TextHashMethod,
+    FileIngestionMethod
+> ContentAddressMethod;
+
+/* Parse and pretty print the algorithm which indicates how the files
+   were ingested, with the the fixed output case not prefixed for back
+   compat. */
+
+std::string makeContentAddressingPrefix(ContentAddressMethod m);
+
+ContentAddressMethod parseContentAddressingPrefix(std::string_view & m);
+
+/* Parse and pretty print a content addressing method and hash in a
+   nicer way, prefixing both cases. */
+
+std::string renderContentAddressMethodAndHash(ContentAddressMethod cam, HashType ht);
+
+std::pair<ContentAddressMethod, HashType> parseContentAddressMethod(std::string_view caMethod);
+
 
 struct TextHash {
     Hash hash;
@@ -27,6 +61,7 @@ struct FixedOutputHash {
     std::string printMethodAlgo() const;
 };
 
+
 /*
   We've accumulated several types of content-addressed paths over the years;
   fixed-output derivations support multiple hash algorithms and serialisation
@@ -43,10 +78,6 @@ typedef std::variant<
     FixedOutputHash // for path computed by makeFixedOutputPath
 > ContentAddress;
 
-/* Compute the prefix to the hash algorithm which indicates how the files were
-   ingested. */
-std::string makeFileIngestionPrefix(const FileIngestionMethod m);
-
 std::string renderContentAddress(ContentAddress ca);
 
 std::string renderContentAddress(std::optional<ContentAddress> ca);
@@ -57,24 +88,6 @@ 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
-  type is only useful in std::variant.
-*/
-struct TextHashMethod { };
-struct FixedOutputHashMethod {
-  FileIngestionMethod fileIngestionMethod;
-  HashType hashType;
-};
-
-typedef std::variant<
-    TextHashMethod,
-    FixedOutputHashMethod
-  > ContentAddressMethod;
-
-ContentAddressMethod parseContentAddressMethod(std::string_view rawCaMethod);
-
-std::string renderContentAddressMethod(ContentAddressMethod caMethod);
 
 /*
  * References set
@@ -92,6 +105,12 @@ struct PathReferences
             && hasSelfReference == other.hasSelfReference;
     }
 
+    bool operator != (const PathReferences<Ref> & other) const
+    {
+        return references != other.references
+            || hasSelfReference != other.hasSelfReference;
+    }
+
     /* Functions to view references + hasSelfReference as one set, mainly for
        compatibility's sake. */
     StorePathSet referencesPossiblyToSelf(const Ref & self) const;
@@ -151,6 +170,14 @@ typedef std::variant<
 
 ContentAddressWithReferences caWithoutRefs(const ContentAddress &);
 
+ContentAddressWithReferences contentAddressFromMethodHashAndRefs(
+    ContentAddressMethod method, Hash && hash, PathReferences<StorePath> && refs);
+
+ContentAddressMethod getContentAddressMethod(const ContentAddressWithReferences & ca);
+Hash getContentAddressHash(const ContentAddressWithReferences & ca);
+
+std::string printMethodAlgo(const ContentAddressWithReferences &);
+
 struct StorePathDescriptor {
     std::string name;
     ContentAddressWithReferences info;

src/libstore/daemon.cc

@@ -380,20 +380,23 @@ 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);
+                auto [contentAddressMethod, hashType] = parseContentAddressMethod(camStr);
                 FramedSource source(from);
                 // TODO this is essentially RemoteStore::addCAToStore. Move it up to Store.
                 return std::visit(overloaded {
-                    [&](TextHashMethod &_) {
+                    [&](TextHashMethod _) {
+                        if (hashType != htSHA256)
+                            throw UnimplementedError("Only SHA-256 is supported for adding text-hashed data, but '%1' was given",
+                                printHashType(hashType));
                         // 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) {
+                    [&](FileIngestionMethod fim) {
                         if (!refs.empty())
                             throw UnimplementedError("cannot yet have refs with flat or nar-hashed data");
-                        auto path = store->addToStoreFromDump(source, name, fohm.fileIngestionMethod, fohm.hashType, repair);
+                        auto path = store->addToStoreFromDump(source, name, fim, hashType, repair);
                         return store->queryPathInfo(path);
                     },
                 }, contentAddressMethod);

src/libstore/derivations.cc

@@ -2,6 +2,7 @@
 #include "store-api.hh"
 #include "globals.hh"
 #include "util.hh"
+#include "split.hh"
 #include "worker-protocol.hh"
 #include "fs-accessor.hh"
 
@@ -26,9 +27,10 @@ std::optional<StorePath> DerivationOutput::path(const Store & store, std::string
 
 
 StorePath DerivationOutputCAFixed::path(const Store & store, std::string_view drvName, std::string_view outputName) const {
-    return store.makeFixedOutputPath(
-        outputPathName(drvName, outputName),
-        { hash, {} });
+    return store.makeFixedOutputPathFromCA(StorePathDescriptor {
+        .name = outputPathName(drvName, outputName),
+        .info = ca,
+    });
 }
 
 
@@ -150,23 +152,19 @@ static StringSet parseStrings(std::istream & str, bool arePaths)
 
 
 static DerivationOutput parseDerivationOutput(const Store & store,
-    std::string_view pathS, std::string_view hashAlgo, std::string_view hash)
+    std::string_view pathS, std::string_view hashAlgo, std::string_view hashS)
 {
     if (hashAlgo != "") {
-        auto method = FileIngestionMethod::Flat;
-        if (string(hashAlgo, 0, 2) == "r:") {
-            method = FileIngestionMethod::Recursive;
-            hashAlgo = hashAlgo.substr(2);
-        }
+        ContentAddressMethod method = parseContentAddressingPrefix(hashAlgo);
         const auto hashType = parseHashType(hashAlgo);
-        if (hash != "") {
+        if (hashS != "") {
             validatePath(pathS);
+            auto hash = Hash::parseNonSRIUnprefixed(hashS, hashType);
             return DerivationOutput {
                 .output = DerivationOutputCAFixed {
-                    .hash = FixedOutputHash {
-                        .method = std::move(method),
-                        .hash = Hash::parseNonSRIUnprefixed(hash, hashType),
-                    },
+                    // FIXME non-trivial fixed refs set
+                    .ca = contentAddressFromMethodHashAndRefs(
+                        method, std::move(hash), {}),
                 },
             };
         } else {
@@ -317,12 +315,12 @@ string Derivation::unparse(const Store & store, bool maskOutputs,
             },
             [&](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));
+                s += ','; printUnquotedString(s, printMethodAlgo(dof.ca));
+                s += ','; printUnquotedString(s, getContentAddressHash(dof.ca).to_string(Base16, false));
             },
             [&](DerivationOutputCAFloating dof) {
                 s += ','; printUnquotedString(s, "");
-                s += ','; printUnquotedString(s, makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
+                s += ','; printUnquotedString(s, makeContentAddressingPrefix(dof.method) + printHashType(dof.hashType));
                 s += ','; printUnquotedString(s, "");
             },
         }, i.second.output);
@@ -482,8 +480,8 @@ DrvHashModulo hashDerivationModulo(Store & store, const Derivation & drv, bool m
         for (const auto & i : drv.outputs) {
             auto & dof = std::get<DerivationOutputCAFixed>(i.second.output);
             auto hash = hashString(htSHA256, "fixed:out:"
-                + dof.hash.printMethodAlgo() + ":"
-                + dof.hash.hash.to_string(Base16, false) + ":"
+                + printMethodAlgo(dof.ca) + ":"
+                + getContentAddressHash(dof.ca).to_string(Base16, false) + ":"
                 + store.printStorePath(dof.path(store, drv.name, i.first)));
             outputHashes.insert_or_assign(i.first, std::move(hash));
         }
@@ -612,12 +610,12 @@ void writeDerivation(Sink & out, const Store & store, const BasicDerivation & dr
             },
             [&](DerivationOutputCAFixed dof) {
                 out << store.printStorePath(dof.path(store, drv.name, i.first))
-                    << dof.hash.printMethodAlgo()
-                    << dof.hash.hash.to_string(Base16, false);
+                    << printMethodAlgo(dof.ca)
+                    << getContentAddressHash(dof.ca).to_string(Base16, false);
             },
             [&](DerivationOutputCAFloating dof) {
                 out << ""
-                    << (makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType))
+                    << (makeContentAddressingPrefix(dof.method) + printHashType(dof.hashType))
                     << "";
             },
         }, i.second.output);

src/libstore/derivations.hh

@@ -27,7 +27,7 @@ struct DerivationOutputInputAddressed
    according to that fixed output. */
 struct DerivationOutputCAFixed
 {
-    FixedOutputHash hash; /* hash used for expected hash computation */
+    ContentAddressWithReferences ca; /* hash and refs used for validating output */
     StorePath path(const Store & store, std::string_view drvName, std::string_view outputName) const;
 };
 
@@ -37,7 +37,7 @@ struct DerivationOutputCAFixed
 struct DerivationOutputCAFloating
 {
     /* information used for expected hash computation */
-    FileIngestionMethod method;
+    ContentAddressMethod method;
     HashType hashType;
 };
 

src/libstore/local-store.cc

@@ -567,7 +567,7 @@ void LocalStore::checkDerivationOutputs(const StorePath & drvPath, const Derivat
                 envHasRightPath(doia.path, i.first);
             },
             [&](DerivationOutputCAFixed dof) {
-                StorePath path = makeFixedOutputPath(drvName, { dof.hash, {} });
+                auto path = dof.path(*this, drvName, i.first);
                 envHasRightPath(path, i.first);
             },
             [&](DerivationOutputCAFloating _) {

src/libstore/misc.cc

@@ -111,9 +111,21 @@ void Store::computeFSClosure(const StorePath & startPath,
 std::optional<ContentAddress> getDerivationCA(const BasicDerivation & drv)
 {
     auto out = drv.outputs.find("out");
-    if (out != drv.outputs.end()) {
-        if (auto v = std::get_if<DerivationOutputCAFixed>(&out->second.output))
-            return v->hash;
+    if (out == drv.outputs.end())
+        return std::nullopt;
+    if (auto dof = std::get_if<DerivationOutputCAFixed>(&out->second.output)) {
+        return std::visit(overloaded {
+        	[&](TextInfo ti) -> std::optional<ContentAddress> {
+        		if (!ti.references.empty())
+        			return std::nullopt;
+        		return static_cast<TextHash>(ti);
+			},
+        	[&](FixedOutputInfo fi) -> std::optional<ContentAddress> {
+        		if (fi.references != PathReferences<StorePath> {})
+        			return std::nullopt;
+        		return static_cast<FixedOutputHash>(fi);
+			},
+        }, dof->ca);
     }
     return std::nullopt;
 }

src/libstore/remote-store.cc

@@ -457,6 +457,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
     Source & dump,
     const string & name,
     ContentAddressMethod caMethod,
+    HashType hashType,
     const StorePathSet & references,
     RepairFlag repair)
 {
@@ -468,7 +469,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
         conn->to
             << wopAddToStore
             << name
-            << renderContentAddressMethod(caMethod);
+            << renderContentAddressMethodAndHash(caMethod, hashType);
         worker_proto::write(*this, conn->to, references);
         conn->to << repair;
 
@@ -484,18 +485,21 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
 
         std::visit(overloaded {
             [&](TextHashMethod thm) -> void {
+                if (hashType != htSHA256)
+                    throw UnimplementedError("Only SHA-256 is supported for adding text-hashed data, but '%1' was given",
+                        printHashType(hashType));
                 std::string s = dump.drain();
                 conn->to << wopAddTextToStore << name << s;
                 worker_proto::write(*this, conn->to, references);
                 conn.processStderr();
             },
-            [&](FixedOutputHashMethod fohm) -> void {
+            [&](FileIngestionMethod fim) -> void {
                 conn->to
                     << wopAddToStore
                     << name
-                    << ((fohm.hashType == htSHA256 && fohm.fileIngestionMethod == FileIngestionMethod::Recursive) ? 0 : 1) /* backwards compatibility hack */
-                    << (fohm.fileIngestionMethod == FileIngestionMethod::Recursive ? 1 : 0)
-                    << printHashType(fohm.hashType);
+                    << ((hashType == htSHA256 && fim == FileIngestionMethod::Recursive) ? 0 : 1) /* backwards compatibility hack */
+                    << (fim == FileIngestionMethod::Recursive ? 1 : 0)
+                    << printHashType(hashType);
 
                 try {
                     conn->to.written = 0;
@@ -503,7 +507,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
                     connections->incCapacity();
                     {
                         Finally cleanup([&]() { connections->decCapacity(); });
-                        if (fohm.fileIngestionMethod == FileIngestionMethod::Recursive) {
+                        if (fim == FileIngestionMethod::Recursive) {
                             dump.drainInto(conn->to);
                         } else {
                             std::string contents = dump.drain();
@@ -536,7 +540,7 @@ StorePath RemoteStore::addToStoreFromDump(Source & dump, const string & name,
         FileIngestionMethod method, HashType hashType, RepairFlag repair)
 {
     StorePathSet references;
-    return addCAToStore(dump, name, FixedOutputHashMethod{ .fileIngestionMethod = method, .hashType = hashType }, references, repair)->path;
+    return addCAToStore(dump, name, method, hashType, references, repair)->path;
 }
 
 
@@ -597,7 +601,7 @@ StorePath RemoteStore::addTextToStore(const string & name, const string & s,
     const StorePathSet & references, RepairFlag repair)
 {
     StringSource source(s);
-    return addCAToStore(source, name, TextHashMethod{}, references, repair)->path;
+    return addCAToStore(source, name, TextHashMethod {}, htSHA256, references, repair)->path;
 }
 
 

src/libstore/remote-store.hh

@@ -68,6 +68,7 @@ public:
         Source & dump,
         const string & name,
         ContentAddressMethod caMethod,
+        HashType hashType,
         const StorePathSet & references,
         RepairFlag repair);
 

src/nix/show-derivation.cc

@@ -76,11 +76,12 @@ struct CmdShowDerivation : InstallablesCommand
                         },
                         [&](DerivationOutputCAFixed dof) {
                             outputObj.attr("path", store->printStorePath(dof.path(*store, drv.name, outputName)));
-                            outputObj.attr("hashAlgo", dof.hash.printMethodAlgo());
-                            outputObj.attr("hash", dof.hash.hash.to_string(Base16, false));
+                            outputObj.attr("hashAlgo", printMethodAlgo(dof.ca));
+                            outputObj.attr("hash", getContentAddressHash(dof.ca).to_string(Base16, false));
+                            // FIXME print refs?
                         },
                         [&](DerivationOutputCAFloating dof) {
-                            outputObj.attr("hashAlgo", makeFileIngestionPrefix(dof.method) + printHashType(dof.hashType));
+                            outputObj.attr("hashAlgo", makeContentAddressingPrefix(dof.method) + printHashType(dof.hashType));
                         },
                     }, output.output);
                 }

tests/local.mk

@@ -35,7 +35,8 @@ nix_tests = \
   recursive.sh \
   describe-stores.sh \
   flakes.sh \
-  content-addressed.sh
+  content-addressed.sh \
+  text-hashed-output.sh
   # parallel.sh
   # build-remote-content-addressed-fixed.sh \
 

tests/text-hashed-output.nix

@@ -0,0 +1,29 @@
+with import ./config.nix;
+
+# A simple content-addressed derivation.
+# The derivation can be arbitrarily modified by passing a different `seed`,
+# but the output will always be the same
+rec {
+  root = mkDerivation {
+    name = "text-hashed-root";
+    buildCommand = ''
+      set -x
+      echo "Building a CA derivation"
+      mkdir -p $out
+      echo "Hello World" > $out/hello
+    '';
+    __contentAddressed = true;
+    outputHashMode = "recursive";
+    outputHashAlgo = "sha256";
+  };
+  dependent = mkDerivation {
+    name = "text-hashed-root.drv";
+    buildCommand = ''
+      echo "Copying the derivation"
+      cp ${root.drvPath} $out
+    '';
+    __contentAddressed = true;
+    outputHashMode = "text";
+    outputHashAlgo = "sha256";
+  };
+}

tests/text-hashed-output.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+# In the corresponding nix file, we have two derivations: the first, named root,
+# is a normal recursive derivation, while the second, named dependent, has the
+# new outputHashMode "text". Note that in "dependent", we don't refer to the
+# build output of root, but only to the path of the drv file. For this reason,
+# we only need to:
+#
+# - instantiate the root derivation
+# - build the dependent derivation
+# - check that the path of the output coincides with that of the original derivation
+
+drv=$(nix-instantiate --experimental-features ca-derivations ./text-hashed-output.nix -A root)
+nix --experimental-features 'nix-command ca-derivations' show-derivation --derivation "$drv"
+
+drvDep=$(nix-instantiate --experimental-features ca-derivations ./text-hashed-output.nix -A dependent)
+nix --experimental-features 'nix-command ca-derivations' show-derivation --derivation "$drvDep"
+
+out1=$(nix-build --experimental-features ca-derivations ./text-hashed-output.nix -A dependent --no-out-link)
+
+nix --experimental-features 'nix-command ca-derivations' path-info $drv --derivation --json | jq
+nix --experimental-features 'nix-command ca-derivations' path-info $out1 --derivation --json | jq
+
+test $out1 == $drv