resolve target expression to self if trying to resolve it got a result in another file (e.g. builtins) (PY-4256)

python/src/com/jetbrains/python/psi/impl/PyTargetReference.java

@@ -1,5 +1,6 @@
 package com.jetbrains.python.psi.impl;
 
+import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiElementResolveResult;
 import com.intellij.psi.ResolveResult;
 import com.intellij.psi.util.PsiTreeUtil;
@@ -21,7 +22,15 @@ public class PyTargetReference extends PyReferenceImpl {
   @Override
   public ResolveResult[] multiResolve(boolean incompleteCode) {
     final ResolveResult[] results = super.multiResolve(incompleteCode);
-    if (results.length > 0) {
+    boolean resolvedToAnotherFile = false;
+    for (ResolveResult result : results) {
+      final PsiElement element = result.getElement();
+      if (element != null && element.getContainingFile() != myElement.getContainingFile()) {
+        resolvedToAnotherFile = true;
+        break;
+      }
+    }
+    if (results.length > 0 && !resolvedToAnotherFile) {
       return results;
     }
     // resolve to self if no other target found

python/testData/resolve/DontResolveTargetToBuiltins.py

@@ -0,0 +1,2 @@
+str = "foo"
+#<ref>

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

@@ -413,4 +413,8 @@ public class PyResolveTest extends PyResolveTestCase {
   public void testSuperclassResolveScope() {  // PY-3554
     assertResolvesTo(PyClass.class, "date", "datetime.py");
   }
+
+  public void testDontResolveTargetToBuiltins() {  // PY-4256
+    assertResolvesTo(PyTargetExpression.class, "str");
+  }
 }