Merge pull request #9915 from 9999years/evaluating-attribute-position

Add position information to `while evaluating the attribute` errors in the debugger

(cherry picked from commit ffe67c86a8ef3695e5c8b9c9800c192ac633dded)
Change-Id: I177ea5ec60898abe09fb9d80d9602b2a32ff8f44

2 files changed, 24 insertions, 1 deletions

diff --git a/doc/manual/rl-next/source-location-in-while-evaluating-attribute.md b/doc/manual/rl-next/source-location-in-while-evaluating-attribute.md
new file mode 100644
index 000000000..0e0b74c5a
--- /dev/null
+++ b/doc/manual/rl-next/source-location-in-while-evaluating-attribute.md
@@ -0,0 +1,23 @@
+---
+synopsis: "In the debugger, `while evaluating the attribute` errors now include position information"
+prs: 9915
+---
+
+Before:
+
+```
+0: while evaluating the attribute 'python311.pythonForBuild.pkgs'
+0x600001522598
+```
+
+After:
+
+```
+0: while evaluating the attribute 'python311.pythonForBuild.pkgs'
+/nix/store/hg65h51xnp74ikahns9hyf3py5mlbbqq-source/overrides/default.nix:132:27
+
+   131|
+   132|       bootstrappingBase = pkgs.${self.python.pythonAttr}.pythonForBuild.pkgs;
+      |                           ^
+   133|     in
+```
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 565688868..debeaf75f 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1457,7 +1457,7 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                 state,
                 *this,
                 env,
-                state.positions[pos2],
+                state.positions[getPos()],
                 "while evaluating the attribute '%1%'",
                 showAttrPath(state, env, attrPath))
             : nullptr;