Be more cautious when identifying typing Literal (#517)

Author: asottile

pyflakes/checker.py

@@ -1457,7 +1457,15 @@ def ignore(self, node):
         STARRED = NAMECONSTANT = NAMEDEXPR = handleChildren
 
     def SUBSCRIPT(self, node):
-        if _is_typing(node.value, 'Literal', self.scopeStack):
+        if (
+                (
+                    isinstance(node.value, ast.Name) and
+                    node.value.id == 'Literal'
+                ) or (
+                    isinstance(node.value, ast.Attribute) and
+                    node.value.attr == 'Literal'
+                )
+        ):
             orig, self._in_typing_literal = self._in_typing_literal, True
             try:
                 self.handleChildren(node)

pyflakes/test/test_type_annotations.py

@@ -507,6 +507,19 @@ def f(x: Literal['some string']) -> None:
             return None
         """)
 
+    @skipIf(version_info < (3,), 'new in Python 3')
+    def test_literal_type_some_other_module(self):
+        """err on the side of false-negatives for types named Literal"""
+        self.flakes("""
+        from my_module import compat
+        from my_module.compat import Literal
+
+        def f(x: compat.Literal['some string']) -> None:
+            return None
+        def g(x: Literal['some string']) -> None:
+            return None
+        """)
+
     @skipIf(version_info < (3,), 'new in Python 3')
     def test_literal_union_type_typing(self):
         self.flakes("""