From 0a1d3c1dd311f94e9d1f56e1aa7fe1ab34314ec1 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 17 Jun 2020 16:54:32 +0200
Subject: [PATCH] Don't provide 'getFlake' if the 'flakes' feature is not
 enabled

---
 src/libexpr/flake/flake.cc |  2 +-
 src/libexpr/primops.cc     |  8 +++++---
 src/libexpr/primops.hh     | 17 +++++++++++++++--
 3 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index fa3185d08..9d516bb87 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -588,7 +588,7 @@ static void prim_getFlake(EvalState & state, const Pos & pos, Value * * args, Va
         v);
 }
 
-static RegisterPrimOp r2("getFlake", 1, prim_getFlake);
+static RegisterPrimOp r2("getFlake", 1, prim_getFlake, "flakes");
 
 }
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index bb1926282..2f1a41a64 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -2202,10 +2202,11 @@ static void prim_splitVersion(EvalState & state, const Pos & pos, Value * * args
 RegisterPrimOp::PrimOps * RegisterPrimOp::primOps;
 
 
-RegisterPrimOp::RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun)
+RegisterPrimOp::RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun,
+    std::optional<std::string> requiredFeature)
 {
     if (!primOps) primOps = new PrimOps;
-    primOps->emplace_back(name, arity, fun);
+    primOps->push_back({name, arity, fun, requiredFeature});
 }
 
 
@@ -2397,7 +2398,8 @@ void EvalState::createBaseEnv()
 
     if (RegisterPrimOp::primOps)
         for (auto & primOp : *RegisterPrimOp::primOps)
-            addPrimOp(std::get<0>(primOp), std::get<1>(primOp), std::get<2>(primOp));
+            if (!primOp.requiredFeature || settings.isExperimentalFeatureEnabled(*primOp.requiredFeature))
+                addPrimOp(primOp.name, primOp.arity, primOp.primOp);
 
     /* Now that we've added all primops, sort the `builtins' set,
        because attribute lookups expect it to be sorted. */
diff --git a/src/libexpr/primops.hh b/src/libexpr/primops.hh
index 05d0792ef..75c460ecf 100644
--- a/src/libexpr/primops.hh
+++ b/src/libexpr/primops.hh
@@ -7,12 +7,25 @@ namespace nix {
 
 struct RegisterPrimOp
 {
-    typedef std::vector<std::tuple<std::string, size_t, PrimOpFun>> PrimOps;
+    struct Info
+    {
+        std::string name;
+        size_t arity;
+        PrimOpFun primOp;
+        std::optional<std::string> requiredFeature;
+    };
+
+    typedef std::vector<Info> PrimOps;
     static PrimOps * primOps;
+
     /* You can register a constant by passing an arity of 0. fun
        will get called during EvalState initialization, so there
        may be primops not yet added and builtins is not yet sorted. */
-    RegisterPrimOp(std::string name, size_t arity, PrimOpFun fun);
+    RegisterPrimOp(
+        std::string name,
+        size_t arity,
+        PrimOpFun fun,
+        std::optional<std::string> requiredFeature = {});
 };
 
 /* These primops are disabled without enableNativeCode, but plugins