resolve works correctly in nested comprehensions (temp fix until parser is rewritten) (PY-3068)

python/src/com/jetbrains/python/psi/resolve/PyResolveUtil.java

@@ -147,8 +147,12 @@ public class PyResolveUtil {
       if ((roof != null) && (seeker != null) && !PsiTreeUtil.isAncestor(roof, seeker, false)) return null;
       // maybe we're capped by a class? param lists are not capped though syntactically inside the function.  
       if (is_outside_param_list && refersFromMethodToClass(capFunction, seeker)) continue;
-      // names defined in a comprehension element are only visible inside it
-      if (seeker instanceof PyComprehensionElement && !PsiTreeUtil.isAncestor(seeker, elt, false)) continue;
+      // names defined in a comprehension element are only visible inside it or the list comp expressions directly above it
+      if (seeker instanceof PyComprehensionElement &&
+          !(seeker.getParent() instanceof PyComprehensionElement) &&
+          !PsiTreeUtil.isAncestor(seeker, elt, false)) {
+        continue;
+      }
       // check what we got
       if (seeker != null) {
         if (!processor.execute(seeker, ResolveState.initial())) {

python/testData/resolve/NestedListComp.py

@@ -0,0 +1,3 @@
+lst1 = [[1,2,3],[4,5,6],[7,8,9]]
+lst2 = [xx for yy in lst1 for xx in yy]
+#                                    <ref>

python/testSrc/com/jetbrains/python/PyResolveTest.java

@@ -405,4 +405,8 @@ public class PyResolveTest extends PyResolveTestCase {
   public void testResolveInGenerator() {
     assertResolvesTo(PyTargetExpression.class, "foo");
   }
+
+  public void testNestedListComp() {  // PY-3068
+    assertResolvesTo(PyTargetExpression.class, "yy");
+  }
 }