save-analysis: walk path expressions

This is actually kinda hard to hit, but it fixes missing the `foo` in `for _ in foo {}`.

src/librustc_save_analysis/dump_visitor.rs

@@ -1369,6 +1369,7 @@ fn visit_ty(&mut self, t: &'l ast::Ty) {
     }
 
     fn visit_expr(&mut self, ex: &'l ast::Expr) {
+        debug!("visit_expr {:?}", ex.node);
         self.process_macro_use(ex.span, ex.id);
         match ex.node {
             ast::ExprKind::Call(ref _f, ref _args) => {
@@ -1462,6 +1463,7 @@ fn visit_expr(&mut self, ex: &'l ast::Expr) {
             ast::ExprKind::WhileLet(ref pattern, ref subexpression, ref block, _) => {
                 let value = self.span.snippet(subexpression.span);
                 self.process_var_decl(pattern, value);
+                debug!("for loop, walk sub-expr: {:?}", subexpression.node);
                 visit::walk_expr(self, subexpression);
                 visit::walk_block(self, block);
             }
@@ -1556,6 +1558,10 @@ fn visit_arm(&mut self, arm: &'l ast::Arm) {
         self.visit_expr(&arm.body);
     }
 
+    fn visit_path(&mut self, p: &'l ast::Path, id: NodeId) {
+        self.process_path(id, p, None);
+    }
+
     fn visit_stmt(&mut self, s: &'l ast::Stmt) {
         self.process_macro_use(s.span, s.id);
         visit::walk_stmt(self, s)