Add experimental feature 'fetch-closure'

src/libexpr/primops/fetchClosure.cc

@@ -7,6 +7,8 @@ namespace nix {
 
 static void prim_fetchClosure(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
+    settings.requireExperimentalFeature(Xp::FetchClosure);
+
     state.forceAttrs(*args[0], pos);
 
     std::optional<std::string> fromStoreUrl;

src/libutil/experimental-features.cc

@@ -11,6 +11,7 @@ std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
     { Xp::NixCommand, "nix-command" },
     { Xp::RecursiveNix, "recursive-nix" },
     { Xp::NoUrlLiterals, "no-url-literals" },
+    { Xp::FetchClosure, "fetch-closure" },
 };
 
 const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)

src/libutil/experimental-features.hh

@@ -19,7 +19,8 @@ enum struct ExperimentalFeature
     Flakes,
     NixCommand,
     RecursiveNix,
-    NoUrlLiterals
+    NoUrlLiterals,
+    FetchClosure,
 };
 
 /**

tests/fetchClosure.sh

@@ -1,5 +1,6 @@
 source common.sh
 
+enableFeatures "fetch-closure"
 needLocalStore "'--no-require-sigs' can’t be used with the daemon"
 
 clearStore