From 18e3d63341bc03e152659a6836a1b52a1241fe57 Mon Sep 17 00:00:00 2001
From: Kevin Amado <kamadorueda@gmail.com>
Date: Fri, 15 Oct 2021 18:56:17 -0500
Subject: [PATCH] fetchTree: add pos to EvalState::forceValue

- This way we improve error messages
  on infinite recursion
- Demo:
  ```nix
  let x = builtins.fetchTree x;
  in x
  ```
- Before:
  ```bash
  $ nix-instantiate --extra-experimental-features flakes --strict
  error: infinite recursion encountered
  ```
- After:
  ```bash
  $ nix-instantiate --extra-experimental-features flakes --strict
  error: infinite recursion encountered

       at /data/github/kamadorueda/nix/test.nix:1:9:

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

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

diff --git a/src/libexpr/primops/fetchTree.cc b/src/libexpr/primops/fetchTree.cc
index f570f19ae..441edd648 100644
--- a/src/libexpr/primops/fetchTree.cc
+++ b/src/libexpr/primops/fetchTree.cc
@@ -97,7 +97,7 @@ static void fetchTree(
     fetchers::Input input;
     PathSet context;
 
-    state.forceValue(*args[0]);
+    state.forceValue(*args[0], pos);
 
     if (args[0]->type() == nAttrs) {
         state.forceAttrs(*args[0], pos);