Only provide builtin.{getFlake,fetchClosure} is the corresponding experimental feature is enabled

This allows writing fallback code like

  if builtins ? fetchClosure then
    builtins.fetchClose { ... }
  else
    builtins.storePath ...

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libexpr/primops/fetchClosure.cc b/src/libexpr/primops/fetchClosure.cc
index 47f40ef33..efeb93daf 100644
--- a/src/libexpr/primops/fetchClosure.cc
+++ b/src/libexpr/primops/fetchClosure.cc
@@ -7,8 +7,6 @@ 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;
@@ -145,8 +143,12 @@ static RegisterPrimOp primop_fetchClosure({
       specifying a binary cache from which the path can be fetched.
       Also, requiring a content-addressed final store path avoids the
       need for users to configure binary cache public keys.
+
+      This function is only available if you enable the experimental
+      feature `fetch-closure`.
     )",
     .fun = prim_fetchClosure,
+    .experimentalFeature = Xp::FetchClosure,
 });
 
 }