Show the exact position of undefined variables

In particular, undefined variable errors in a "with" previously didn't
show *any* position information, so this should help a lot in those
cases.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 7db0a15fa30f..e555a5dff051 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -109,6 +109,7 @@ struct ExprPath : Expr
 
 struct ExprVar : Expr
 {
+    Pos pos;
     Symbol name;
 
     /* Whether the variable comes from an environment (e.g. a rec, let
@@ -124,7 +125,7 @@ struct ExprVar : Expr
     unsigned int level;
     unsigned int displ;
 
-    ExprVar(const Symbol & name) : name(name) { };
+    ExprVar(const Pos & pos, const Symbol & name) : pos(pos), name(name) { };
     COMMON_METHODS
     Value * maybeThunk(EvalState & state, Env & env);
 };