Fix extend issue being stuck in endless loop

Fixes #3006

Author: mgreter

src/eval_selectors.cpp

@@ -46,10 +46,10 @@ namespace Sass {
   SelectorList* Eval::operator()(ComplexSelector* s)
   {
     bool implicit_parent = !exp.old_at_root_without_rule;
-    if (is_in_selector_schema) exp.pushToSelectorStack({});
+    if (is_in_selector_schema) exp.pushNullSelector();
     SelectorListObj other = s->resolve_parent_refs(
-      exp.getSelectorStack(), traces, implicit_parent);
-    if (is_in_selector_schema) exp.popFromSelectorStack();
+      exp.getOriginalStack(), traces, implicit_parent);
+    if (is_in_selector_schema) exp.popNullSelector();
 
     for (size_t i = 0; i < other->length(); i++) {
       ComplexSelectorObj sel = other->at(i);

src/expand.cpp

@@ -38,17 +38,17 @@ namespace Sass {
     env_stack.push_back(env);
     block_stack.push_back(nullptr);
     call_stack.push_back({});
-    if (stack == NULL) { pushToSelectorStack({}); }
+    if (stack == NULL) { pushNullSelector(); }
     else {
       for (auto item : *stack) {
-        if (item.isNull()) pushToSelectorStack({});
+        if (item.isNull()) pushNullSelector();
         else pushToSelectorStack(item);
       }
     }
-    if (originals == NULL) { pushToOriginalStack({}); }
+    if (originals == NULL) { pushNullSelector(); }
     else {
       for (auto item : *stack) {
-        if (item.isNull()) pushToOriginalStack({});
+        if (item.isNull()) pushNullSelector();
         else pushToOriginalStack(item);
       }
     }
@@ -62,6 +62,23 @@ namespace Sass {
     return 0;
   }
 
+  void Expand::pushNullSelector()
+  {
+    pushToSelectorStack({});
+    pushToOriginalStack({});
+  }
+
+  void Expand::popNullSelector()
+  {
+    popFromOriginalStack();
+    popFromSelectorStack();
+  }
+
+  SelectorStack Expand::getOriginalStack()
+  {
+    return originalStack;
+  }
+
   SelectorStack Expand::getSelectorStack()
   {
     return selector_stack;
@@ -153,15 +170,15 @@ namespace Sass {
       Block* bb = operator()(r->block());
       Keyframe_Rule_Obj k = SASS_MEMORY_NEW(Keyframe_Rule, r->pstate(), bb);
       if (r->schema()) {
-        pushToSelectorStack({});
+        pushNullSelector();
         k->name(eval(r->schema()));
-        popFromSelectorStack();
+        popNullSelector();
       }
       else if (r->selector()) {
         if (SelectorListObj s = r->selector()) {
-          pushToSelectorStack({});
+          pushNullSelector();
           k->name(eval(s));
-          popFromSelectorStack();
+          popNullSelector();
         }
       }
 
@@ -288,10 +305,10 @@ namespace Sass {
     Block* ab = a->block();
     SelectorList* as = a->selector();
     Expression* av = a->value();
-    pushToSelectorStack({});
+    pushNullSelector();
     if (av) av = av->perform(&eval);
     if (as) as = eval(as);
-    popFromSelectorStack();
+    popNullSelector();
     Block* bb = ab ? operator()(ab) : NULL;
     Directive* aa = SASS_MEMORY_NEW(Directive,
                                   a->pstate(),

src/expand.hpp

@@ -22,7 +22,10 @@ namespace Sass {
     SelectorListObj& selector();
     SelectorListObj& original();
     SelectorListObj popFromSelectorStack();
+    SelectorStack getOriginalStack();
     SelectorStack getSelectorStack();
+    void pushNullSelector();
+    void popNullSelector();
     void pushToSelectorStack(SelectorListObj selector);
 
     SelectorListObj popFromOriginalStack();

src/extender.hpp

@@ -126,8 +126,8 @@ namespace Sass {
     std::unordered_map<
       SimpleSelectorObj,
       size_t,
-      ObjHash,
-      ObjEquality
+      ObjPtrHash,
+      ObjPtrEquality
     > sourceSpecificity;
 
     // ##########################################################################