From eac5841970737b799c55ec78f6ace6d80762ff04 Mon Sep 17 00:00:00 2001
From: Shea Levy <shea@shealevy.com>
Date: Thu, 15 May 2014 11:30:46 -0400
Subject: [PATCH] Provide a more useful error message when a dynamic attr
 lookup fails

---
 src/libexpr/eval.cc | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 0f7e8e385..81abe5b61 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -757,8 +757,16 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
                 }
             } else {
                 state.forceAttrs(*vAttrs, pos);
-                if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end())
-                    throwEvalError("attribute `%1%' missing, at %2%", showAttrPath(attrPath), pos);
+                if ((j = vAttrs->attrs->find(name)) == vAttrs->attrs->end()) {
+                    AttrPath staticPath;
+                    AttrPath::const_iterator j;
+                    for (j = attrPath.begin(); j != i; ++j)
+                        staticPath.push_back(AttrName(getName(*j, state, env)));
+                    staticPath.push_back(AttrName(getName(*j, state, env)));
+                    for (j = j + 1; j != attrPath.end(); ++j)
+                        staticPath.push_back(*j);
+                    throwEvalError("attribute `%1%' missing, at %2%", showAttrPath(staticPath), pos);
+                }
             }
             vAttrs = j->value;
             pos2 = j->pos;