Allow method return types to be changed when the overridden type is NoReturn.

PiperOrigin-RevId: 447558672

Author: rchen152

pytype/overriding_checks.py

@@ -327,10 +327,10 @@ def _check_default_values(method_signature, base_signature):
     base_default = abstract_utils.get_atomic_value(base_default_value)
     method_default = abstract_utils.get_atomic_value(method_default_value)
 
-    # Unsolvable or Unknown matches anything.
-    if isinstance(base_default, (abstract.Unsolvable, abstract.Unknown)):
+    # Unsolvable, Unknown, or Empty matches anything.
+    if isinstance(base_default, abstract.AMBIGUOUS_OR_EMPTY):
       continue
-    if isinstance(method_default, (abstract.Unsolvable, abstract.Unknown)):
+    if isinstance(method_default, abstract.AMBIGUOUS_OR_EMPTY):
       continue
 
     if base_default != method_default:
@@ -351,6 +351,10 @@ def _check_return_types(method_signature, base_signature, is_subtype):
     # Return type not annotated in either of the two methods.
     return None
 
+  if (isinstance(base_return_type, abstract.AMBIGUOUS_OR_EMPTY) or
+      isinstance(method_return_type, abstract.AMBIGUOUS_OR_EMPTY)):
+    return None
+
   # Return type of the overriding method must be a subtype of the
   # return type of the overridden method.
   if not is_subtype(method_return_type, base_return_type):

pytype/tests/test_overriding.py

@@ -198,6 +198,19 @@ def f(self) -> str:  # signature-mismatch
           return ''
     """)
 
+  def test_return_type_matches_empty(self):
+    with self.DepTree([("foo.py", """
+      class Foo:
+        def f(self):
+          raise NotImplementedError()
+    """)]):
+      self.Check("""
+        import foo
+        class Bar(foo.Foo):
+          def f(self) -> None:
+            pass
+      """)
+
   def test_pytdclass_signature_match(self):
     self.Check("""
       class Foo(list):