repl: add repl-flake experimental feature for gating

src/libutil/experimental-features.cc

@@ -13,6 +13,7 @@ std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
     { Xp::RecursiveNix, "recursive-nix" },
     { Xp::NoUrlLiterals, "no-url-literals" },
     { Xp::FetchClosure, "fetch-closure" },
+    { Xp::ReplFlake, "repl-flake" },
 };
 
 const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)

src/libutil/experimental-features.hh

@@ -22,6 +22,7 @@ enum struct ExperimentalFeature
     RecursiveNix,
     NoUrlLiterals,
     FetchClosure,
+    ReplFlake,
 };
 
 /**

src/nix/repl.cc

@@ -897,7 +897,7 @@ struct CmdRepl : InstallablesCommand
     }
     void prepare()
     {
-        if (!settings.isExperimentalFeatureEnabled(Xp::Flakes) && !(file) && this->_installables.size() >= 1) {
+        if (!settings.isExperimentalFeatureEnabled(Xp::ReplFlake) && !(file) && this->_installables.size() >= 1) {
             warn("future versions of Nix will require using `--file` to load a file");
             if (this->_installables.size() > 1)
                 warn("more than one input file is not currently supported");