`TextHashMethod` -> `TextIngestionMethod`, gate with XP feature

I suppose we can use `dynamic-derivations` for the few things we neeed.

10 files changed, 46 insertions, 24 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 2476b7e73..fc397db33 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1105,8 +1105,10 @@ drvName, Bindings * attrs, Value & v)
         auto handleHashMode = [&](const std::string_view s) {
             if (s == "recursive") ingestionMethod = FileIngestionMethod::Recursive;
             else if (s == "flat") ingestionMethod = FileIngestionMethod::Flat;
-            else if (s == "text") ingestionMethod = TextHashMethod {};
-            else
+            else if (s == "text") {
+                experimentalFeatureSettings.require(Xp::DynamicDerivations);
+                ingestionMethod = TextIngestionMethod {};
+            } else
                 state.debugThrowLastTrace(EvalError({
                     .msg = hintfmt("invalid value '%s' for 'outputHashMode' attribute", s),
                     .errPos = state.positions[noPos]
@@ -1274,11 +1276,16 @@ drvName, Bindings * attrs, Value & v)
         }));
 
     /* Check whether the derivation name is valid. */
-    if (isDerivation(drvName) && ingestionMethod != ContentAddressMethod { TextHashMethod { } })
+    if (isDerivation(drvName) &&
+        !(ingestionMethod == ContentAddressMethod { TextIngestionMethod { } } &&
+          outputs.size() == 1 &&
+          *(outputs.begin()) == "out"))
+    {
         state.debugThrowLastTrace(EvalError({
             .msg = hintfmt("derivation names are allowed to end in '%s' only if they produce a single derivation file", drvExtension),
             .errPos = state.positions[noPos]
         }));
+    }
 
     if (outputHash) {
         /* Handle fixed-output derivations.
diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index 0a208750e..7a424fbfc 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -2427,7 +2427,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
                     "output path %1% without valid stats info",
                     actualPath);
             if (outputHash.method == ContentAddressMethod { FileIngestionMethod::Flat } ||
-                outputHash.method == ContentAddressMethod { TextHashMethod {} })
+                outputHash.method == ContentAddressMethod { TextIngestionMethod {} })
             {
                 /* The output path should be a regular file without execute permission. */
                 if (!S_ISREG(st->st_mode) || (st->st_mode & S_IXUSR) != 0)
@@ -2441,7 +2441,7 @@ SingleDrvOutputs LocalDerivationGoal::registerOutputs()
             std::string oldHashPart { scratchPath->hashPart() };
             HashModuloSink caSink { outputHash.hashType, oldHashPart };
             std::visit(overloaded {
-                [&](const TextHashMethod &) {
+                [&](const TextIngestionMethod &) {
                     readFile(actualPath, caSink);
                 },
                 [&](const FileIngestionMethod & m2) {
diff --git a/src/libstore/content-address.cc b/src/libstore/content-address.cc
index 8c04dd285..2bde23e79 100644
--- a/src/libstore/content-address.cc
+++ b/src/libstore/content-address.cc
@@ -23,7 +23,7 @@ std::string makeFileIngestionPrefix(FileIngestionMethod m)
 
 std::string ContentAddressMethod::renderPrefix() const {
     return std::visit(overloaded {
-        [](TextHashMethod) -> std::string { return "text:"; },
+        [](TextIngestionMethod) -> std::string { return "text:"; },
         [](FileIngestionMethod m2) {
              /* Not prefixed for back compat with things that couldn't produce text before. */
             return makeFileIngestionPrefix(m2);
@@ -37,7 +37,7 @@ ContentAddressMethod ContentAddressMethod::parsePrefix(std::string_view & m)
     if (splitPrefix(m, "r:"))
         method = FileIngestionMethod::Recursive;
     else if (splitPrefix(m, "text:"))
-        method = TextHashMethod {};
+        method = TextIngestionMethod {};
     return method;
 }
 
@@ -59,7 +59,7 @@ std::string ContentAddress::render() const
 std::string ContentAddressMethod::render(HashType ht) const
 {
     return std::visit(overloaded {
-        [&](const TextHashMethod & th) {
+        [&](const TextIngestionMethod & th) {
             return std::string{"text:"} + printHashType(ht);
         },
         [&](const FileIngestionMethod & fim) {
@@ -96,7 +96,7 @@ static std::pair<ContentAddressMethod, HashType> parseContentAddressMethodPrefix
         // No parsing of the ingestion method, "text" only support flat.
         HashType hashType = parseHashType_();
         return {
-            TextHashMethod {},
+            TextIngestionMethod {},
             std::move(hashType),
         };
     } else if (prefix == "fixed") {
@@ -120,7 +120,7 @@ ContentAddress ContentAddress::parse(std::string_view rawCa) {
     auto hashType = hashType_; // work around clang bug
 
     return std::visit(overloaded {
-        [&](TextHashMethod &) {
+        [&](TextIngestionMethod &) {
             return ContentAddress(TextHash {
                 .hash = Hash::parseNonSRIUnprefixed(rest, hashType)
             });
@@ -158,7 +158,7 @@ ContentAddressWithReferences ContentAddressWithReferences::fromParts(
     ContentAddressMethod  method, Hash hash, StoreReferences refs)
 {
     return std::visit(overloaded {
-        [&](TextHashMethod _) -> ContentAddressWithReferences {
+        [&](TextIngestionMethod _) -> ContentAddressWithReferences {
             if (refs.self)
                 throw UsageError("Cannot have a self reference with text hashing scheme");
             return TextInfo {
@@ -182,7 +182,7 @@ ContentAddressMethod ContentAddressWithReferences::getMethod() const
 {
     return std::visit(overloaded {
         [](const TextInfo & th) -> ContentAddressMethod {
-            return TextHashMethod {};
+            return TextIngestionMethod {};
         },
         [](const FixedOutputInfo & fsh) -> ContentAddressMethod {
             return fsh.hash.method;
diff --git a/src/libstore/content-address.hh b/src/libstore/content-address.hh
index 962b63e83..8668acacf 100644
--- a/src/libstore/content-address.hh
+++ b/src/libstore/content-address.hh
@@ -22,7 +22,7 @@ namespace nix {
  * Somewhat obscure, used by \ref Derivation derivations and
  * `builtins.toFile` currently.
  */
-struct TextHashMethod : std::monostate { };
+struct TextIngestionMethod : std::monostate { };
 
 /**
  * An enumeration of the main ways we can serialize file system
@@ -57,7 +57,7 @@ std::string makeFileIngestionPrefix(FileIngestionMethod m);
 struct ContentAddressMethod
 {
     typedef std::variant<
-        TextHashMethod,
+        TextIngestionMethod,
         FileIngestionMethod
     > Raw;
 
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index d3b9988c9..31e2e2af5 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -406,7 +406,7 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
                 FramedSource source(from);
                 // TODO this is essentially RemoteStore::addCAToStore. Move it up to Store.
                 return std::visit(overloaded {
-                    [&](const TextHashMethod &) {
+                    [&](const TextIngestionMethod &) {
                         if (hashType != htSHA256)
                             throw UnimplementedError("Only SHA-256 is supported for adding text-hashed data, but '%1' was given",
                                 printHashType(hashType));
diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index fc76ae7ad..1f5f78964 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -216,6 +216,8 @@ static DerivationOutput parseDerivationOutput(const Store & store,
 {
     if (hashAlgo != "") {
         ContentAddressMethod method = ContentAddressMethod::parsePrefix(hashAlgo);
+        if (method == TextIngestionMethod {})
+            experimentalFeatureSettings.require(Xp::DynamicDerivations);
         const auto hashType = parseHashType(hashAlgo);
         if (hashS == "impure") {
             experimentalFeatureSettings.require(Xp::ImpureDerivations);
diff --git a/src/libstore/derivations.hh b/src/libstore/derivations.hh
index 65901ec6d..b36e4ea91 100644
--- a/src/libstore/derivations.hh
+++ b/src/libstore/derivations.hh
@@ -339,12 +339,14 @@ struct Derivation : BasicDerivation
         Store & store,
         const std::map<std::pair<StorePath, std::string>, StorePath> & inputDrvOutputs) const;
 
-    /* Check that the derivation is valid and does not present any
-       illegal states.
-
-       This is mainly a matter of checking the outputs, where our C++
-       representation supports all sorts of combinations we do not yet
-       allow. */
+    /**
+     * Check that the derivation is valid and does not present any
+     * illegal states.
+     *
+     * This is mainly a matter of checking the outputs, where our C++
+     * representation supports all sorts of combinations we do not yet
+     * allow.
+     */
     void checkInvariants(Store & store, const StorePath & drvPath) const;
 
     Derivation() = default;
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index ff5348830..b3f5251f2 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -629,7 +629,7 @@ ref<const ValidPathInfo> RemoteStore::addCAToStore(
         if (repair) throw Error("repairing is not supported when building through the Nix daemon protocol < 1.25");
 
         std::visit(overloaded {
-            [&](const TextHashMethod & thm) -> void {
+            [&](const TextIngestionMethod & thm) -> void {
                 if (hashType != htSHA256)
                     throw UnimplementedError("Only SHA-256 is supported for adding text-hashed data, but '%1' was given",
                         printHashType(hashType));
@@ -782,7 +782,7 @@ StorePath RemoteStore::addTextToStore(
     RepairFlag repair)
 {
     StringSource source(s);
-    return addCAToStore(source, name, TextHashMethod {}, htSHA256, references, repair)->path;
+    return addCAToStore(source, name, TextIngestionMethod {}, htSHA256, references, repair)->path;
 }
 
 void RemoteStore::registerDrvOutput(const Realisation & info)
diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
index bd1899662..ad0ec0427 100644
--- a/src/libutil/experimental-features.cc
+++ b/src/libutil/experimental-features.cc
@@ -12,7 +12,7 @@ struct ExperimentalFeatureDetails
     std::string_view description;
 };
 
-constexpr std::array<ExperimentalFeatureDetails, 12> xpFeatureDetails = {{
+constexpr std::array<ExperimentalFeatureDetails, 13> xpFeatureDetails = {{
     {
         .tag = Xp::CaDerivations,
         .name = "ca-derivations",
@@ -199,6 +199,16 @@ constexpr std::array<ExperimentalFeatureDetails, 12> xpFeatureDetails = {{
             networking.
         )",
     },
+    {
+        .tag = Xp::DynamicDerivations,
+        .name = "dynamic-derivations",
+        .description = R"(
+            Allow the use of a few things related to dynamic derivations:
+
+              - "text hashing" derivation outputs, so we can build .drv
+                files.
+        )",
+    },
 }};
 
 static_assert(
diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh
index 3c00bc4e5..409100592 100644
--- a/src/libutil/experimental-features.hh
+++ b/src/libutil/experimental-features.hh
@@ -29,6 +29,7 @@ enum struct ExperimentalFeature
     Cgroups,
     DiscardReferences,
     DaemonTrustOverride,
+    DynamicDerivations,
 };
 
 /**