Cleanup ContentAddressMethod to match docs

The old `std::variant` is bad because we aren't adding a new case to
`FileIngestionMethod` so much as we are defining a separate concept ---
store object content addressing rather than file system object content
addressing. As such, it is more correct to just create a fresh
enumeration.

Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

src/libexpr/eval.cc

@@ -2303,7 +2303,7 @@ StorePath EvalState::copyPathToStore(NixStringContext & context, const SourcePat
                 path.resolveSymlinks(),
                 settings.readOnlyMode ? FetchMode::DryRun : FetchMode::Copy,
                 path.baseName(),
-                FileIngestionMethod::NixArchive,
+                ContentAddressMethod::Raw::NixArchive,
                 nullptr,
                 repair);
             allowPath(dstPath);

src/libexpr/primops.cc

@@ -1209,7 +1209,7 @@ static void derivationStrictInternal(
         auto handleHashMode = [&](const std::string_view s) {
             if (s == "recursive") {
                 // back compat, new name is "nar"
-                ingestionMethod = FileIngestionMethod::NixArchive;
+                ingestionMethod = ContentAddressMethod::Raw::NixArchive;
             } else try {
                 ingestionMethod = ContentAddressMethod::parse(s);
             } catch (UsageError &) {
@@ -1217,9 +1217,9 @@ static void derivationStrictInternal(
                     "invalid value '%s' for 'outputHashMode' attribute", s
                 ).atPos(v).debugThrow();
             }
-            if (ingestionMethod == TextIngestionMethod {})
+            if (ingestionMethod == ContentAddressMethod::Raw::Text)
                 experimentalFeatureSettings.require(Xp::DynamicDerivations);
-            if (ingestionMethod == FileIngestionMethod::Git)
+            if (ingestionMethod == ContentAddressMethod::Raw::Git)
                 experimentalFeatureSettings.require(Xp::GitHashing);
         };
 
@@ -1391,7 +1391,7 @@ static void derivationStrictInternal(
 
     /* Check whether the derivation name is valid. */
     if (isDerivation(drvName) &&
-        !(ingestionMethod == ContentAddressMethod { TextIngestionMethod { } } &&
+        !(ingestionMethod == ContentAddressMethod::Raw::Text &&
           outputs.size() == 1 &&
           *(outputs.begin()) == "out"))
     {
@@ -1413,7 +1413,7 @@ static void derivationStrictInternal(
 
         auto h = newHashAllowEmpty(*outputHash, outputHashAlgo);
 
-        auto method = ingestionMethod.value_or(FileIngestionMethod::Flat);
+        auto method = ingestionMethod.value_or(ContentAddressMethod::Raw::Flat);
 
         DerivationOutput::CAFixed dof {
             .ca = ContentAddress {
@@ -1432,7 +1432,7 @@ static void derivationStrictInternal(
                 .atPos(v).debugThrow();
 
         auto ha = outputHashAlgo.value_or(HashAlgorithm::SHA256);
-        auto method = ingestionMethod.value_or(FileIngestionMethod::NixArchive);
+        auto method = ingestionMethod.value_or(ContentAddressMethod::Raw::NixArchive);
 
         for (auto & i : outputs) {
             drv.env[i] = hashPlaceholder(i);
@@ -2208,7 +2208,7 @@ static void prim_toFile(EvalState & state, const PosIdx pos, Value * * args, Val
         })
         : ({
             StringSource s { contents };
-            state.store->addToStoreFromDump(s, name, FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, refs, state.repair);
+            state.store->addToStoreFromDump(s, name, FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, refs, state.repair);
         });
 
     /* Note: we don't need to add `context' to the context of the
@@ -2391,7 +2391,7 @@ static void prim_filterSource(EvalState & state, const PosIdx pos, Value * * arg
         "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");
 
-    addPath(state, pos, path.baseName(), path, args[0], FileIngestionMethod::NixArchive, std::nullopt, v, context);
+    addPath(state, pos, path.baseName(), path, args[0], ContentAddressMethod::Raw::NixArchive, std::nullopt, v, context);
 }
 
 static RegisterPrimOp primop_filterSource({
@@ -2454,7 +2454,7 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
     std::optional<SourcePath> path;
     std::string name;
     Value * filterFun = nullptr;
-    ContentAddressMethod method = FileIngestionMethod::NixArchive;
+    auto method = ContentAddressMethod::Raw::NixArchive;
     std::optional<Hash> expectedHash;
     NixStringContext context;
 
@@ -2470,8 +2470,8 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
             state.forceFunction(*(filterFun = attr.value), attr.pos, "while evaluating the `filter` parameter passed to builtins.path");
         else if (n == "recursive")
             method = state.forceBool(*attr.value, attr.pos, "while evaluating the `recursive` attribute passed to builtins.path")
-                ? FileIngestionMethod::NixArchive
+                ? ContentAddressMethod::Raw::NixArchive
-                : FileIngestionMethod::Flat;
+                : ContentAddressMethod::Raw::Flat;
         else if (n == "sha256")
             expectedHash = newHashAllowEmpty(state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `sha256` attribute passed to builtins.path"), HashAlgorithm::SHA256);
         else

src/libfetchers/fetch-to-store.hh

@@ -18,7 +18,7 @@ StorePath fetchToStore(
     const SourcePath & path,
     FetchMode mode,
     std::string_view name = "source",
-    ContentAddressMethod method = FileIngestionMethod::NixArchive,
+    ContentAddressMethod method = ContentAddressMethod::Raw::NixArchive,
     PathFilter * filter = nullptr,
     RepairFlag repair = NoRepair);
 

src/libfetchers/mercurial.cc

@@ -213,7 +213,7 @@ struct MercurialInputScheme : InputScheme
                 auto storePath = store->addToStore(
                     input.getName(),
                     {getFSSourceAccessor(), CanonPath(actualPath)},
-                    FileIngestionMethod::NixArchive, HashAlgorithm::SHA256, {},
+                    ContentAddressMethod::Raw::NixArchive, HashAlgorithm::SHA256, {},
                     filter);
 
                 return storePath;

src/libstore/content-address.cc

@@ -8,6 +8,7 @@ std::string_view makeFileIngestionPrefix(FileIngestionMethod m)
 {
     switch (m) {
     case FileIngestionMethod::Flat:
+        // Not prefixed for back compat
         return "";
     case FileIngestionMethod::NixArchive:
         return "r:";
@@ -15,91 +16,128 @@ std::string_view makeFileIngestionPrefix(FileIngestionMethod m)
         experimentalFeatureSettings.require(Xp::GitHashing);
         return "git:";
     default:
-        throw Error("impossible, caught both cases");
+        assert(false);
     }
 }
 
 std::string_view ContentAddressMethod::render() const
 {
-    return std::visit(overloaded {
+    switch (raw) {
-        [](TextIngestionMethod) -> std::string_view { return "text"; },
+    case ContentAddressMethod::Raw::Text:
-        [](FileIngestionMethod m2) {
+        return "text";
-             /* Not prefixed for back compat with things that couldn't produce text before. */
+    case ContentAddressMethod::Raw::Flat:
-            return renderFileIngestionMethod(m2);
+    case ContentAddressMethod::Raw::NixArchive:
-        },
+    case ContentAddressMethod::Raw::Git:
-    }, raw);
+        return renderFileIngestionMethod(getFileIngestionMethod());
+    default:
+        assert(false);
+    }
+}
+
+/**
+ * **Not surjective**
+ *
+ * This is not exposed because `FileIngestionMethod::Flat` maps to
+ * `ContentAddressMethod::Raw::Flat` and
+ * `ContentAddressMethod::Raw::Text` alike. We can thus only safely use
+ * this when the latter is ruled out (e.g. because it is already
+ * handled).
+ */
+static ContentAddressMethod fileIngestionMethodToContentAddressMethod(FileIngestionMethod m)
+{
+    switch (m) {
+    case FileIngestionMethod::Flat:
+        return ContentAddressMethod::Raw::Flat;
+    case FileIngestionMethod::NixArchive:
+        return ContentAddressMethod::Raw::NixArchive;
+    case FileIngestionMethod::Git:
+        return ContentAddressMethod::Raw::Git;
+    default:
+        assert(false);
+    }
 }
 
 ContentAddressMethod ContentAddressMethod::parse(std::string_view m)
 {
     if (m == "text")
-        return TextIngestionMethod {};
+        return ContentAddressMethod::Raw::Text;
     else
-        return parseFileIngestionMethod(m);
+        return fileIngestionMethodToContentAddressMethod(
+            parseFileIngestionMethod(m));
 }
 
 std::string_view ContentAddressMethod::renderPrefix() const
 {
-    return std::visit(overloaded {
+    switch (raw) {
-        [](TextIngestionMethod) -> std::string_view { return "text:"; },
+    case ContentAddressMethod::Raw::Text:
-        [](FileIngestionMethod m2) {
+        return "text:";
-             /* Not prefixed for back compat with things that couldn't produce text before. */
+    case ContentAddressMethod::Raw::Flat:
-            return makeFileIngestionPrefix(m2);
+    case ContentAddressMethod::Raw::NixArchive:
-        },
+    case ContentAddressMethod::Raw::Git:
-    }, raw);
+        return makeFileIngestionPrefix(getFileIngestionMethod());
+    default:
+        assert(false);
+    }
 }
 
 ContentAddressMethod ContentAddressMethod::parsePrefix(std::string_view & m)
 {
     if (splitPrefix(m, "r:")) {
-        return FileIngestionMethod::NixArchive;
+        return ContentAddressMethod::Raw::NixArchive;
     }
     else if (splitPrefix(m, "git:")) {
         experimentalFeatureSettings.require(Xp::GitHashing);
-        return FileIngestionMethod::Git;
+        return ContentAddressMethod::Raw::Git;
     }
     else if (splitPrefix(m, "text:")) {
-        return TextIngestionMethod {};
+        return ContentAddressMethod::Raw::Text;
+    }
+    return ContentAddressMethod::Raw::Flat;
+}
+
+/**
+ * This is slightly more mindful of forward compat in that it uses `fixed:`
+ * rather than just doing a raw empty prefix or `r:`, which doesn't "save room"
+ * for future changes very well.
+ */
+static std::string renderPrefixModern(const ContentAddressMethod & ca)
+{
+    switch (ca.raw) {
+    case ContentAddressMethod::Raw::Text:
+        return "text:";
+    case ContentAddressMethod::Raw::Flat:
+    case ContentAddressMethod::Raw::NixArchive:
+    case ContentAddressMethod::Raw::Git:
+        return "fixed:" + makeFileIngestionPrefix(ca.getFileIngestionMethod());
+    default:
+        assert(false);
     }
-    return FileIngestionMethod::Flat;
 }
 
 std::string ContentAddressMethod::renderWithAlgo(HashAlgorithm ha) const
 {
-    return std::visit(overloaded {
+    return renderPrefixModern(*this) + printHashAlgo(ha);
-        [&](const TextIngestionMethod & th) {
-            return std::string{"text:"} + printHashAlgo(ha);
-        },
-        [&](const FileIngestionMethod & fim) {
-            return "fixed:" + makeFileIngestionPrefix(fim) + printHashAlgo(ha);
-        }
-    }, raw);
 }
 
 FileIngestionMethod ContentAddressMethod::getFileIngestionMethod() const
 {
-    return std::visit(overloaded {
+    switch (raw) {
-        [&](const TextIngestionMethod & th) {
+    case ContentAddressMethod::Raw::Flat:
-            return FileIngestionMethod::Flat;
+        return FileIngestionMethod::Flat;
-        },
+    case ContentAddressMethod::Raw::NixArchive:
-        [&](const FileIngestionMethod & fim) {
+        return FileIngestionMethod::NixArchive;
-            return fim;
+    case ContentAddressMethod::Raw::Git:
-        }
+        return FileIngestionMethod::Git;
-    }, raw);
+    case ContentAddressMethod::Raw::Text:
+        return FileIngestionMethod::Flat;
+    default:
+        assert(false);
+    }
 }
 
 std::string ContentAddress::render() const
 {
-    return std::visit(overloaded {
+    return renderPrefixModern(method) + this->hash.to_string(HashFormat::Nix32, true);
-        [](const TextIngestionMethod &) -> std::string {
-            return "text:";
-        },
-        [](const FileIngestionMethod & method) {
-            return "fixed:"
-                + makeFileIngestionPrefix(method);
-        },
-    }, method.raw)
-        + this->hash.to_string(HashFormat::Nix32, true);
 }
 
 /**
@@ -130,17 +168,17 @@ static std::pair<ContentAddressMethod, HashAlgorithm> parseContentAddressMethodP
         // No parsing of the ingestion method, "text" only support flat.
         HashAlgorithm hashAlgo = parseHashAlgorithm_();
         return {
-            TextIngestionMethod {},
+            ContentAddressMethod::Raw::Text,
             std::move(hashAlgo),
         };
     } else if (prefix == "fixed") {
         // Parse method
-        auto method = FileIngestionMethod::Flat;
+        auto method = ContentAddressMethod::Raw::Flat;
         if (splitPrefix(rest, "r:"))
-            method = FileIngestionMethod::NixArchive;
+            method = ContentAddressMethod::Raw::NixArchive;
         else if (splitPrefix(rest, "git:")) {
             experimentalFeatureSettings.require(Xp::GitHashing);
-            method = FileIngestionMethod::Git;
+            method = ContentAddressMethod::Raw::Git;
         }
         HashAlgorithm hashAlgo = parseHashAlgorithm_();
         return {
@@ -201,57 +239,58 @@ size_t StoreReferences::size() const
 
 ContentAddressWithReferences ContentAddressWithReferences::withoutRefs(const ContentAddress & ca) noexcept
 {
-    return std::visit(overloaded {
+    switch (ca.method.raw) {
-        [&](const TextIngestionMethod &) -> ContentAddressWithReferences {
+    case ContentAddressMethod::Raw::Text:
-            return TextInfo {
+        return TextInfo {
-                .hash = ca.hash,
+            .hash = ca.hash,
-                .references = {},
+            .references = {},
-            };
+        };
-        },
+    case ContentAddressMethod::Raw::Flat:
-        [&](const FileIngestionMethod & method) -> ContentAddressWithReferences {
+    case ContentAddressMethod::Raw::NixArchive:
-            return FixedOutputInfo {
+    case ContentAddressMethod::Raw::Git:
-                .method = method,
+        return FixedOutputInfo {
-                .hash = ca.hash,
+            .method = ca.method.getFileIngestionMethod(),
-                .references = {},
+            .hash = ca.hash,
-            };
+            .references = {},
-        },
+        };
-    }, ca.method.raw);
+    default:
+        assert(false);
+    }
 }
 
 ContentAddressWithReferences ContentAddressWithReferences::fromParts(
     ContentAddressMethod method, Hash hash, StoreReferences refs)
 {
-    return std::visit(overloaded {
+    switch (method.raw) {
-        [&](TextIngestionMethod _) -> ContentAddressWithReferences {
+    case ContentAddressMethod::Raw::Text:
-            if (refs.self)
+        if (refs.self)
-                throw Error("self-reference not allowed with text hashing");
+            throw Error("self-reference not allowed with text hashing");
-            return ContentAddressWithReferences {
+        return TextInfo {
-                TextInfo {
+            .hash = std::move(hash),
-                    .hash = std::move(hash),
+            .references = std::move(refs.others),
-                    .references = std::move(refs.others),
+        };
-                }
+    case ContentAddressMethod::Raw::Flat:
-            };
+    case ContentAddressMethod::Raw::NixArchive:
-        },
+    case ContentAddressMethod::Raw::Git:
-        [&](FileIngestionMethod m2) -> ContentAddressWithReferences {
+        return FixedOutputInfo {
-            return ContentAddressWithReferences {
+            .method = method.getFileIngestionMethod(),
-                FixedOutputInfo {
+            .hash = std::move(hash),
-                    .method = m2,
+            .references = std::move(refs),
-                    .hash = std::move(hash),
+        };
-                    .references = std::move(refs),
+    default:
-                }
+        assert(false);
-            };
+    }
-        },
-    }, method.raw);
 }
 
 ContentAddressMethod ContentAddressWithReferences::getMethod() const
 {
     return std::visit(overloaded {
         [](const TextInfo & th) -> ContentAddressMethod {
-            return TextIngestionMethod {};
+            return ContentAddressMethod::Raw::Text;
         },
         [](const FixedOutputInfo & fsh) -> ContentAddressMethod {
-            return fsh.method;
+            return fileIngestionMethodToContentAddressMethod(
+                fsh.method);
         },
     }, raw);
 }

src/libstore/content-address.hh

@@ -5,7 +5,6 @@
 #include "hash.hh"
 #include "path.hh"
 #include "file-content-address.hh"
-#include "comparator.hh"
 #include "variant-wrapper.hh"
 
 namespace nix {
@@ -14,24 +13,6 @@ 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.
-*/
-
-/**
- * The single way we can serialize "text" file system objects.
- *
- * Somewhat obscure, used by \ref Derivation derivations and
- * `builtins.toFile` currently.
- *
- * TextIngestionMethod is identical to FileIngestionMethod::Fixed except that
- * the former may not have self-references and is tagged `text:${algo}:${hash}`
- * rather than `fixed:${algo}:${hash}`.  The contents of the store path are
- * ingested and hashed identically, aside from the slightly different tag and
- * restriction on self-references.
- */
-struct TextIngestionMethod : std::monostate { };
-
 /**
  * Compute the prefix to the hash algorithm which indicates how the
  * files were ingested.
@@ -48,14 +29,51 @@ std::string_view makeFileIngestionPrefix(FileIngestionMethod m);
  */
 struct ContentAddressMethod
 {
-    typedef std::variant<
+    enum struct Raw {
-        TextIngestionMethod,
+        /**
-        FileIngestionMethod
+         * Calculate a store path using the `FileIngestionMethod::Flat`
-    > Raw;
+         * hash of the file system objects, and references.
+         *
+         * See `store-object/content-address.md#method-flat` in the
+         * manual.
+         */
+        Flat,
+
+        /**
+         * Calculate a store path using the
+         * `FileIngestionMethod::NixArchive` hash of the file system
+         * objects, and references.
+         *
+         * See `store-object/content-address.md#method-flat` in the
+         * manual.
+         */
+        NixArchive,
+
+        /**
+         * Calculate a store path using the `FileIngestionMethod::Git`
+         * hash of the file system objects, and references.
+         *
+         * Part of `ExperimentalFeature::GitHashing`.
+         *
+         * See `store-object/content-address.md#method-git` in the
+         * manual.
+         */
+        Git,
+
+        /**
+         * Calculate a store path using the `FileIngestionMethod::Flat`
+         * hash of the file system objects, and references, but in a
+         * different way than `ContentAddressMethod::Raw::Flat`.
+         *
+         * See `store-object/content-address.md#method-text` in the
+         * manual.
+         */
+        Text,
+    };
 
     Raw raw;
 
-    GENERATE_CMP(ContentAddressMethod, me->raw);
+    auto operator <=>(const ContentAddressMethod &) const = default;
 
     MAKE_WRAPPER_CONSTRUCTOR(ContentAddressMethod);
 
@@ -141,7 +159,7 @@ struct ContentAddress
      */
     Hash hash;
 
-    GENERATE_CMP(ContentAddress, me->method, me->hash);
+    auto operator <=>(const ContentAddress &) const = default;
 
     /**
      * Compute the content-addressability assertion
@@ -200,7 +218,7 @@ struct StoreReferences
      */
     size_t size() const;
 
-    GENERATE_CMP(StoreReferences, me->self, me->others);
+    auto operator <=>(const StoreReferences &) const = default;
 };
 
 // This matches the additional info that we need for makeTextPath
@@ -217,7 +235,7 @@ struct TextInfo
      */
     StorePathSet references;
 
-    GENERATE_CMP(TextInfo, me->hash, me->references);
+    auto operator <=>(const TextInfo &) const = default;
 };
 
 struct FixedOutputInfo
@@ -237,7 +255,7 @@ struct FixedOutputInfo
      */
     StoreReferences references;
 
-    GENERATE_CMP(FixedOutputInfo, me->hash, me->references);
+    auto operator <=>(const FixedOutputInfo &) const = default;
 };
 
 /**
@@ -254,7 +272,7 @@ struct ContentAddressWithReferences
 
     Raw raw;
 
-    GENERATE_CMP(ContentAddressWithReferences, me->raw);
+    auto operator <=>(const ContentAddressWithReferences &) const = default;
 
     MAKE_WRAPPER_CONSTRUCTOR(ContentAddressWithReferences);
 

src/libstore/daemon.cc

@@ -435,19 +435,21 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         } else {
             HashAlgorithm hashAlgo;
             std::string baseName;
-            FileIngestionMethod method;
+            ContentAddressMethod method;
             {
                 bool fixed;
                 uint8_t recursive;
                 std::string hashAlgoRaw;
                 from >> baseName >> fixed /* obsolete */ >> recursive >> hashAlgoRaw;
-                if (recursive > (uint8_t) FileIngestionMethod::NixArchive)
+                if (recursive > true)
                     throw Error("unsupported FileIngestionMethod with value of %i; you may need to upgrade nix-daemon", recursive);
-                method = FileIngestionMethod { recursive };
+                method = recursive
+                    ? ContentAddressMethod::Raw::NixArchive
+                    : ContentAddressMethod::Raw::Flat;
                 /* Compatibility hack. */
                 if (!fixed) {
                     hashAlgoRaw = "sha256";
-                    method = FileIngestionMethod::NixArchive;
+                    method = ContentAddressMethod::Raw::NixArchive;
                 }
                 hashAlgo = parseHashAlgo(hashAlgoRaw);
             }
@@ -500,7 +502,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
         logger->startWork();
         auto path = ({
             StringSource source { s };
-            store->addToStoreFromDump(source, suffix, FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, refs, NoRepair);
+            store->addToStoreFromDump(source, suffix, FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, refs, NoRepair);
         });
         logger->stopWork();
         to << store->printStorePath(path);

src/libstore/derivations.cc

@@ -150,7 +150,7 @@ StorePath writeDerivation(Store & store,
         })
         : ({
             StringSource s { contents };
-            store.addToStoreFromDump(s, suffix, FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, references, repair);
+            store.addToStoreFromDump(s, suffix, FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, references, repair);
         });
 }
 
@@ -274,7 +274,7 @@ static DerivationOutput parseDerivationOutput(
 {
     if (hashAlgoStr != "") {
         ContentAddressMethod method = ContentAddressMethod::parsePrefix(hashAlgoStr);
-        if (method == TextIngestionMethod {})
+        if (method == ContentAddressMethod::Raw::Text)
             xpSettings.require(Xp::DynamicDerivations);
         const auto hashAlgo = parseHashAlgo(hashAlgoStr);
         if (hashS == "impure") {
@@ -1249,7 +1249,7 @@ DerivationOutput DerivationOutput::fromJSON(
     auto methodAlgo = [&]() -> std::pair<ContentAddressMethod, HashAlgorithm> {
         auto & method_ = getString(valueAt(json, "method"));
         ContentAddressMethod method = ContentAddressMethod::parse(method_);
-        if (method == TextIngestionMethod {})
+        if (method == ContentAddressMethod::Raw::Text)
             xpSettings.require(Xp::DynamicDerivations);
 
         auto & hashAlgo_ = getString(valueAt(json, "hashAlgo"));

src/libstore/local-store.cc

@@ -1253,7 +1253,7 @@ StorePath LocalStore::addToStoreFromDump(
     std::filesystem::path tempDir;
     AutoCloseFD tempDirFd;
 
-    bool methodsMatch = ContentAddressMethod(FileIngestionMethod(dumpMethod)) == hashMethod;
+    bool methodsMatch = static_cast<FileIngestionMethod>(dumpMethod) == hashMethod.getFileIngestionMethod();
 
     /* If the methods don't match, our streaming hash of the dump is the
        wrong sort, and we need to rehash. */

src/libstore/path-info.cc

@@ -48,15 +48,21 @@ std::optional<ContentAddressWithReferences> ValidPathInfo::contentAddressWithRef
     if (! ca)
         return std::nullopt;
 
-    return std::visit(overloaded {
+    switch (ca->method.raw) {
-        [&](const TextIngestionMethod &) -> ContentAddressWithReferences {
+        case ContentAddressMethod::Raw::Text:
+        {
             assert(references.count(path) == 0);
             return TextInfo {
                 .hash = ca->hash,
                 .references = references,
             };
-        },
+        }
-        [&](const FileIngestionMethod & m2) -> ContentAddressWithReferences {
+
+        case ContentAddressMethod::Raw::Flat:
+        case ContentAddressMethod::Raw::NixArchive:
+        case ContentAddressMethod::Raw::Git:
+        default:
+        {
             auto refs = references;
             bool hasSelfReference = false;
             if (refs.count(path)) {
@@ -64,15 +70,15 @@ std::optional<ContentAddressWithReferences> ValidPathInfo::contentAddressWithRef
                 refs.erase(path);
             }
             return FixedOutputInfo {
-                .method = m2,
+                .method = ca->method.getFileIngestionMethod(),
                 .hash = ca->hash,
                 .references = {
                     .others = std::move(refs),
                     .self = hasSelfReference,
                 },
             };
-        },
+        }
-    }, ca->method.raw);
+    }
 }
 
 bool ValidPathInfo::isContentAddressed(const Store & store) const
@@ -127,22 +133,18 @@ ValidPathInfo::ValidPathInfo(
       : UnkeyedValidPathInfo(narHash)
       , path(store.makeFixedOutputPathFromCA(name, ca))
 {
+    this->ca = ContentAddress {
+        .method = ca.getMethod(),
+        .hash = ca.getHash(),
+    };
     std::visit(overloaded {
         [this](TextInfo && ti) {
             this->references = std::move(ti.references);
-            this->ca = ContentAddress {
-                .method = TextIngestionMethod {},
-                .hash = std::move(ti.hash),
-            };
         },
         [this](FixedOutputInfo && foi) {
             this->references = std::move(foi.references.others);
             if (foi.references.self)
                 this->references.insert(path);
-            this->ca = ContentAddress {
-                .method = std::move(foi.method),
-                .hash = std::move(foi.hash),
-            };
         },
     }, std::move(ca).raw);
 }

src/libstore/remote-store.cc

@@ -392,8 +392,9 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
     else {
         if (repair) throw Error("repairing is not supported when building through the Nix daemon protocol < 1.25");
 
-        std::visit(overloaded {
+        switch (caMethod.raw) {
-            [&](const TextIngestionMethod & thm) -> void {
+            case ContentAddressMethod::Raw::Text:
+            {
                 if (hashAlgo != HashAlgorithm::SHA256)
                     throw UnimplementedError("When adding text-hashed data called '%s', only SHA-256 is supported but '%s' was given",
                         name, printHashAlgo(hashAlgo));
@@ -401,8 +402,14 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
                 conn->to << WorkerProto::Op::AddTextToStore << name << s;
                 WorkerProto::write(*this, *conn, references);
                 conn.processStderr();
-            },
+                break;
-            [&](const FileIngestionMethod & fim) -> void {
+            }
+            case ContentAddressMethod::Raw::Flat:
+            case ContentAddressMethod::Raw::NixArchive:
+            case ContentAddressMethod::Raw::Git:
+            default:
+            {
+                auto fim = caMethod.getFileIngestionMethod();
                 conn->to
                     << WorkerProto::Op::AddToStore
                     << name
@@ -432,9 +439,9 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
                         } catch (EndOfFile & e) { }
                     throw;
                 }
-
+                break;
             }
-        }, caMethod.raw);
+        }
         auto path = parseStorePath(readString(conn->from));
         // Release our connection to prevent a deadlock in queryPathInfo().
         conn_.reset();

src/libstore/store-api.cc

@@ -356,7 +356,7 @@ ValidPathInfo Store::addToStoreSlow(
     RegularFileSink fileSink { caHashSink };
     TeeSink unusualHashTee { narHashSink, caHashSink };
 
-    auto & narSink = method == FileIngestionMethod::NixArchive && hashAlgo != HashAlgorithm::SHA256
+    auto & narSink = method == ContentAddressMethod::Raw::NixArchive && hashAlgo != HashAlgorithm::SHA256
         ? static_cast<Sink &>(unusualHashTee)
         : narHashSink;
 
@@ -384,9 +384,9 @@ ValidPathInfo Store::addToStoreSlow(
        finish. */
     auto [narHash, narSize] = narHashSink.finish();
 
-    auto hash = method == FileIngestionMethod::NixArchive && hashAlgo == HashAlgorithm::SHA256
+    auto hash = method == ContentAddressMethod::Raw::NixArchive && hashAlgo == HashAlgorithm::SHA256
         ? narHash
-        : method == FileIngestionMethod::Git
+        : method == ContentAddressMethod::Raw::Git
         ? git::dumpHash(hashAlgo, srcPath).hash
         : caHashSink.finish().first;
 

src/libstore/store-api.hh

@@ -441,7 +441,7 @@ public:
     virtual StorePath addToStore(
         std::string_view name,
         const SourcePath & path,
-        ContentAddressMethod method = FileIngestionMethod::NixArchive,
+        ContentAddressMethod method = ContentAddressMethod::Raw::NixArchive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = StorePathSet(),
         PathFilter & filter = defaultPathFilter,
@@ -455,7 +455,7 @@ public:
     ValidPathInfo addToStoreSlow(
         std::string_view name,
         const SourcePath & path,
-        ContentAddressMethod method = FileIngestionMethod::NixArchive,
+        ContentAddressMethod method = ContentAddressMethod::Raw::NixArchive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = StorePathSet(),
         std::optional<Hash> expectedCAHash = {});
@@ -481,7 +481,7 @@ public:
         Source & dump,
         std::string_view name,
         FileSerialisationMethod dumpMethod = FileSerialisationMethod::NixArchive,
-        ContentAddressMethod hashMethod = FileIngestionMethod::NixArchive,
+        ContentAddressMethod hashMethod = ContentAddressMethod::Raw::NixArchive,
         HashAlgorithm hashAlgo = HashAlgorithm::SHA256,
         const StorePathSet & references = StorePathSet(),
         RepairFlag repair = NoRepair) = 0;

src/libutil/file-content-address.hh

@@ -117,6 +117,8 @@ enum struct FileIngestionMethod : uint8_t {
     /**
      * Git hashing.
      *
+     * Part of `ExperimentalFeature::GitHashing`.
+     *
      * See `file-system-object/content-address.md#serial-git` in the
      * manual.
      */

src/nix-env/user-env.cc

@@ -115,7 +115,7 @@ bool createUserEnv(EvalState & state, PackageInfos & elems,
         std::string str2 = str.str();
         StringSource source { str2 };
         state.store->addToStoreFromDump(
-            source, "env-manifest.nix", FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, references);
+            source, "env-manifest.nix", FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, references);
     });
 
     /* Get the environment builder expression. */

src/nix-store/nix-store.cc

@@ -194,10 +194,10 @@ static void opAdd(Strings opFlags, Strings opArgs)
    store. */
 static void opAddFixed(Strings opFlags, Strings opArgs)
 {
-    auto method = FileIngestionMethod::Flat;
+    ContentAddressMethod method = ContentAddressMethod::Raw::Flat;
 
     for (auto & i : opFlags)
-        if (i == "--recursive") method = FileIngestionMethod::NixArchive;
+        if (i == "--recursive") method = ContentAddressMethod::Raw::NixArchive;
         else throw UsageError("unknown flag '%1%'", i);
 
     if (opArgs.empty())

src/nix/add-to-store.cc

@@ -12,7 +12,7 @@ struct CmdAddToStore : MixDryRun, StoreCommand
 {
     Path path;
     std::optional<std::string> namePart;
-    ContentAddressMethod caMethod = FileIngestionMethod::NixArchive;
+    ContentAddressMethod caMethod = ContentAddressMethod::Raw::NixArchive;
     HashAlgorithm hashAlgo = HashAlgorithm::SHA256;
 
     CmdAddToStore()
@@ -68,7 +68,7 @@ struct CmdAddFile : CmdAddToStore
 {
     CmdAddFile()
     {
-        caMethod = FileIngestionMethod::Flat;
+        caMethod = ContentAddressMethod::Raw::Flat;
     }
 
     std::string description() override

src/nix/develop.cc

@@ -238,7 +238,7 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     auto getEnvShPath = ({
         StringSource source { getEnvSh };
         evalStore->addToStoreFromDump(
-            source, "get-env.sh", FileSerialisationMethod::Flat, TextIngestionMethod {}, HashAlgorithm::SHA256, {});
+            source, "get-env.sh", FileSerialisationMethod::Flat, ContentAddressMethod::Raw::Text, HashAlgorithm::SHA256, {});
     });
 
     drv.args = {store->printStorePath(getEnvShPath)};

src/nix/prefetch.cc

@@ -57,7 +57,9 @@ std::tuple<StorePath, Hash> prefetchFile(
         bool unpack,
         bool executable)
 {
-    auto ingestionMethod = unpack || executable ? FileIngestionMethod::NixArchive : FileIngestionMethod::Flat;
+    ContentAddressMethod method = unpack || executable
+        ? ContentAddressMethod::Raw::NixArchive
+        : ContentAddressMethod::Raw::Flat;
 
     /* Figure out a name in the Nix store. */
     if (!name) {
@@ -73,11 +75,10 @@ std::tuple<StorePath, Hash> prefetchFile(
        the store. */
     if (expectedHash) {
         hashAlgo = expectedHash->algo;
-        storePath = store->makeFixedOutputPath(*name, FixedOutputInfo {
+        storePath = store->makeFixedOutputPathFromCA(*name, ContentAddressWithReferences::fromParts(
-            .method = ingestionMethod,
+            method,
-            .hash = *expectedHash,
+            *expectedHash,
-            .references = {},
+            {}));
-        });
         if (store->isValidPath(*storePath))
             hash = expectedHash;
         else
@@ -128,7 +129,7 @@ std::tuple<StorePath, Hash> prefetchFile(
 
         auto info = store->addToStoreSlow(
             *name, PosixSourceAccessor::createAtRoot(tmpFile),
-            ingestionMethod, hashAlgo, {}, expectedHash);
+            method, hashAlgo, {}, expectedHash);
         storePath = info.path;
         assert(info.ca);
         hash = info.ca->hash;

src/perl/lib/Nix/Store.xs

@@ -335,7 +335,7 @@ SV *
 StoreWrapper::addToStore(char * srcPath, int recursive, char * algo)
     PPCODE:
         try {
-            auto method = recursive ? FileIngestionMethod::NixArchive : FileIngestionMethod::Flat;
+            auto method = recursive ? ContentAddressMethod::Raw::NixArchive : ContentAddressMethod::Raw::Flat;
             auto path = THIS->store->addToStore(
                 std::string(baseNameOf(srcPath)),
                 PosixSourceAccessor::createAtRoot(srcPath),

tests/unit/libstore/common-protocol.cc

@@ -83,15 +83,15 @@ CHARACTERIZATION_TEST(
     "content-address",
     (std::tuple<ContentAddress, ContentAddress, ContentAddress> {
         ContentAddress {
-            .method = TextIngestionMethod {},
+            .method = ContentAddressMethod::Raw::Text,
             .hash = hashString(HashAlgorithm::SHA256, "Derive(...)"),
         },
         ContentAddress {
-            .method = FileIngestionMethod::Flat,
+            .method = ContentAddressMethod::Raw::Flat,
             .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
         },
         ContentAddress {
-            .method = FileIngestionMethod::NixArchive,
+            .method = ContentAddressMethod::Raw::NixArchive,
             .hash = hashString(HashAlgorithm::SHA256, "(...)"),
         },
     }))
@@ -178,7 +178,7 @@ CHARACTERIZATION_TEST(
         std::nullopt,
         std::optional {
             ContentAddress {
-                .method = FileIngestionMethod::Flat,
+                .method = ContentAddressMethod::Raw::Flat,
                 .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
             },
         },

tests/unit/libstore/content-address.cc

@@ -9,11 +9,11 @@ namespace nix {
  * --------------------------------------------------------------------------*/
 
 TEST(ContentAddressMethod, testRoundTripPrintParse_1) {
-    for (const ContentAddressMethod & cam : {
+    for (ContentAddressMethod cam : {
-        ContentAddressMethod { TextIngestionMethod {} },
+        ContentAddressMethod::Raw::Text,
-        ContentAddressMethod { FileIngestionMethod::Flat },
+        ContentAddressMethod::Raw::Flat,
-        ContentAddressMethod { FileIngestionMethod::NixArchive },
+        ContentAddressMethod::Raw::NixArchive,
-        ContentAddressMethod { FileIngestionMethod::Git },
+        ContentAddressMethod::Raw::Git,
     }) {
         EXPECT_EQ(ContentAddressMethod::parse(cam.render()), cam);
     }

tests/unit/libstore/derivation.cc

@@ -108,7 +108,7 @@ TEST_JSON(DerivationTest, inputAddressed,
 TEST_JSON(DerivationTest, caFixedFlat,
     (DerivationOutput::CAFixed {
         .ca = {
-            .method = FileIngestionMethod::Flat,
+            .method = ContentAddressMethod::Raw::Flat,
             .hash = Hash::parseAnyPrefixed("sha256-iUUXyRY8iW7DGirb0zwGgf1fRbLA7wimTJKgP7l/OQ8="),
         },
     }),
@@ -117,7 +117,7 @@ TEST_JSON(DerivationTest, caFixedFlat,
 TEST_JSON(DerivationTest, caFixedNAR,
     (DerivationOutput::CAFixed {
         .ca = {
-            .method = FileIngestionMethod::NixArchive,
+            .method = ContentAddressMethod::Raw::NixArchive,
             .hash = Hash::parseAnyPrefixed("sha256-iUUXyRY8iW7DGirb0zwGgf1fRbLA7wimTJKgP7l/OQ8="),
         },
     }),
@@ -126,6 +126,7 @@ TEST_JSON(DerivationTest, caFixedNAR,
 TEST_JSON(DynDerivationTest, caFixedText,
     (DerivationOutput::CAFixed {
         .ca = {
+            .method = ContentAddressMethod::Raw::Text,
             .hash = Hash::parseAnyPrefixed("sha256-iUUXyRY8iW7DGirb0zwGgf1fRbLA7wimTJKgP7l/OQ8="),
         },
     }),
@@ -133,7 +134,7 @@ TEST_JSON(DynDerivationTest, caFixedText,
 
 TEST_JSON(CaDerivationTest, caFloating,
     (DerivationOutput::CAFloating {
-        .method = FileIngestionMethod::NixArchive,
+        .method = ContentAddressMethod::Raw::NixArchive,
         .hashAlgo = HashAlgorithm::SHA256,
     }),
     "drv-name", "output-name")
@@ -144,7 +145,7 @@ TEST_JSON(DerivationTest, deferred,
 
 TEST_JSON(ImpureDerivationTest, impure,
     (DerivationOutput::Impure {
-        .method = FileIngestionMethod::NixArchive,
+        .method = ContentAddressMethod::Raw::NixArchive,
         .hashAlgo = HashAlgorithm::SHA256,
     }),
     "drv-name", "output-name")

tests/unit/libstore/serve-protocol.cc

@@ -55,15 +55,15 @@ VERSIONED_CHARACTERIZATION_TEST(
     defaultVersion,
     (std::tuple<ContentAddress, ContentAddress, ContentAddress> {
         ContentAddress {
-            .method = TextIngestionMethod {},
+            .method = ContentAddressMethod::Raw::Text,
             .hash = hashString(HashAlgorithm::SHA256, "Derive(...)"),
         },
         ContentAddress {
-            .method = FileIngestionMethod::Flat,
+            .method = ContentAddressMethod::Raw::Flat,
             .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
         },
         ContentAddress {
-            .method = FileIngestionMethod::NixArchive,
+            .method = ContentAddressMethod::Raw::NixArchive,
             .hash = hashString(HashAlgorithm::SHA256, "(...)"),
         },
     }))
@@ -398,7 +398,7 @@ VERSIONED_CHARACTERIZATION_TEST(
         std::nullopt,
         std::optional {
             ContentAddress {
-                .method = FileIngestionMethod::Flat,
+                .method = ContentAddressMethod::Raw::Flat,
                 .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
             },
         },

tests/unit/libstore/worker-protocol.cc

@@ -56,15 +56,15 @@ VERSIONED_CHARACTERIZATION_TEST(
     defaultVersion,
     (std::tuple<ContentAddress, ContentAddress, ContentAddress> {
         ContentAddress {
-            .method = TextIngestionMethod {},
+            .method = ContentAddressMethod::Raw::Text,
             .hash = hashString(HashAlgorithm::SHA256, "Derive(...)"),
         },
         ContentAddress {
-            .method = FileIngestionMethod::Flat,
+            .method = ContentAddressMethod::Raw::Flat,
             .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
         },
         ContentAddress {
-            .method = FileIngestionMethod::NixArchive,
+            .method = ContentAddressMethod::Raw::NixArchive,
             .hash = hashString(HashAlgorithm::SHA256, "(...)"),
         },
     }))
@@ -598,7 +598,7 @@ VERSIONED_CHARACTERIZATION_TEST(
         std::nullopt,
         std::optional {
             ContentAddress {
-                .method = FileIngestionMethod::Flat,
+                .method = ContentAddressMethod::Raw::Flat,
                 .hash = hashString(HashAlgorithm::SHA1, "blob blob..."),
             },
         },