From 48aa57549d514432d6621c1e29f051951eca2d7f Mon Sep 17 00:00:00 2001
From: Yorick van Pelt <yorick@yorickvanpelt.nl>
Date: Mon, 28 Aug 2023 18:20:23 +0200
Subject: [PATCH] primops: change to std::function, allowing the passing of
 user data

---
 src/libexpr/eval.hh    | 3 ++-
 src/libexpr/primops.cc | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index f15d19653..a1b0e58e4 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -17,6 +17,7 @@
 #include <optional>
 #include <unordered_map>
 #include <mutex>
+#include <functional>
 
 namespace nix {
 
@@ -72,7 +73,7 @@ struct PrimOp
     /**
      * Implementation of the primop.
      */
-    PrimOpFun fun;
+    std::function<std::remove_pointer<PrimOpFun>::type> fun;
 
     /**
      * Optional experimental for this to be gated on.
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index db4237130..a619a627a 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -3402,8 +3402,11 @@ static void prim_sort(EvalState & state, const PosIdx pos, Value * * args, Value
            callFunction. */
         /* TODO: (layus) this is absurd. An optimisation like this
            should be outside the lambda creation */
-        if (args[0]->isPrimOp() && args[0]->primOp->fun == prim_lessThan)
-            return CompareValues(state, noPos, "while evaluating the ordering function passed to builtins.sort")(a, b);
+        if (args[0]->isPrimOp()) {
+            auto ptr = args[0]->primOp->fun.target<decltype(&prim_lessThan)>();
+            if (ptr && *ptr == prim_lessThan)
+                return CompareValues(state, noPos, "while evaluating the ordering function passed to builtins.sort")(a, b);
+        }
 
         Value * vs[] = {a, b};
         Value vBool;