Don't use any syntactic sugar for dynamic attrs

This doesn't change any functionality but moves some behavior out of the
parser and into the evaluator in order to simplify the code.

Signed-off-by: Shea Levy <shea@shealevy.com>

src/libexpr/nixexpr.cc

@@ -155,12 +155,19 @@ std::ostream & operator << (std::ostream & str, const Pos & pos)
 
 string showAttrPath(const AttrPath & attrPath)
 {
-    string s;
+    std::ostringstream out;
+    bool first = true;
     foreach (AttrPath::const_iterator, i, attrPath) {
-        if (!s.empty()) s += '.';
-        s += *i;
+        if (!first)
+            out << '.';
+        else
+            first = false;
+        if (i->symbol.set())
+            out << i->symbol;
+        else
+            out << "\"${" << *i->expr << "}\"";
     }
-    return s;
+    return out.str();
 }
 
 
@@ -220,11 +227,17 @@ void ExprSelect::bindVars(const StaticEnv & env)
 {
     e->bindVars(env);
     if (def) def->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
 }
 
 void ExprOpHasAttr::bindVars(const StaticEnv & env)
 {
     e->bindVars(env);
+    foreach (AttrPath::iterator, i, attrPath)
+        if (!i->symbol.set())
+            i->expr->bindVars(env);
 }
 
 void ExprAttrs::bindVars(const StaticEnv & env)