Fix some edge case with parent selector evaluation

Fixes #1170

Author: mgreter

debugger.hpp

@@ -264,6 +264,9 @@ inline void debug_ast(AST_Node* node, string ind = "", Env* env = 0)
     cerr << ind << "If " << block;
     cerr << " (" << pstate_source_position(node) << ")";
     cerr << " " << block->tabs() << endl;
+    debug_ast(block->predicate(), ind + " = ");
+    debug_ast(block->consequent(), ind + " <>");
+    debug_ast(block->alternative(), ind + " ><");
   } else if (dynamic_cast<Return*>(node)) {
     Return* block = dynamic_cast<Return*>(node);
     cerr << ind << "Return " << block;

eval.cpp

@@ -1047,9 +1047,13 @@ namespace Sass {
 
   Expression* Eval::operator()(Parent_Selector* p)
   {
+    // no idea why both calls are needed
     Selector* s = p->perform(contextualize);
+    if (!s) s = p->selector()->perform(contextualize);
     // access to parent selector may return 0
     Selector_List* l = static_cast<Selector_List*>(s);
+    // some spec tests cause this (might be a valid case!)
+    // if (!s) { cerr << "Parent Selector eval error" << endl; }
     if (!s) { l = new (ctx.mem) Selector_List(p->pstate()); }
     return l->perform(listize);
   }