If we cannot infer the type of '__new__', return a weak class type (PY-10893)

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

@@ -408,6 +408,12 @@ public class PyCallExpressionHelper {
             if (t != null && !(t instanceof PyNoneType)) {
               return t;
             }
+            if (cls != null && t == null) {
+              final PyFunction newMethod = cls.findMethodByName(PyNames.NEW, true);
+              if (newMethod != null && !PyBuiltinCache.getInstance(call).hasInBuiltins(newMethod)) {
+                return PyUnionType.createWeakType(new PyClassTypeImpl(cls, false));
+              }
+            }
           }
           if (cls != null) {
             return new PyClassTypeImpl(cls, false);

python/testData/inspections/PyUnresolvedReferencesInspection/CustomNewReturnInAnotherModule/a.py

@@ -0,0 +1,4 @@
+from b import C
+
+c = C()
+c.foo()

python/testData/inspections/PyUnresolvedReferencesInspection/CustomNewReturnInAnotherModule/b.py

@@ -0,0 +1,8 @@
+class C(object):
+    def __new__(cls):
+        return D()
+
+
+class D(object):
+    def foo(self):
+        pass

python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java

@@ -298,6 +298,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyTestCase {
     doMultiFileTest("a.py");
   }
 
+  // PY-10893
+  public void testCustomNewReturnInAnotherModule() {
+    doMultiFileTest("a.py");
+  }
+
   private void doTest() {
     myFixture.configureByFile(TEST_DIRECTORY + getTestName(true) + ".py");
     myFixture.enableInspections(PyUnresolvedReferencesInspection.class);