From 1bdeef83958251e728abe9398b4286cb6b5e9551 Mon Sep 17 00:00:00 2001
From: Kevin Amado <kamadorueda@gmail.com>
Date: Thu, 14 Oct 2021 23:23:04 -0500
Subject: [PATCH] add pos to EvalState::forceValue

- This way we improve error messages
  on infinite recursion
- Demo:
  ```nix
  let
    x = builtins.fetchMercurial x;
  in
  x
  ```
- Before:
  ```bash
  $ nix-instantiate --show-trace --strict
  error: infinite recursion encountered
  ```
- After:
  ```bash
  nix-instantiate --show-trace --strict
  error: infinite recursion encountered

       at /data/github/kamadorueda/test/default.nix:2:7:

            1| let
            2|   x = builtins.fetchMercurial x;
             |       ^
            3| in
  ```

Mentions: #3505
---
 src/libexpr/primops/fetchMercurial.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libexpr/primops/fetchMercurial.cc b/src/libexpr/primops/fetchMercurial.cc
index 1cd481243..c23480853 100644
--- a/src/libexpr/primops/fetchMercurial.cc
+++ b/src/libexpr/primops/fetchMercurial.cc
@@ -15,7 +15,7 @@ static void prim_fetchMercurial(EvalState & state, const Pos & pos, Value * * ar
     std::string name = "source";
     PathSet context;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {