gh-20418: Fix false positive override error for overloaded methods with narrower return types

mypy/checker.py

@@ -2497,6 +2497,22 @@ def check_override(
         # Use boolean variable to clarify code.
         fail = False
         op_method_wider_note = False
+        if isinstance(override, Overloaded) and isinstance(original, CallableType):
+            if not self.is_forward_op_method(name):
+                if all(is_subtype(item.ret_type, original.ret_type) for item in override.items):
+                    # Return True to maintain backwards compatibility with existing mypy_primer
+                    return True
+                if isinstance(node, OverloadedFuncDef) and node.impl and node.impl.type:
+                    impl_type = node.impl.type
+                    if is_subtype(impl_type, original, ignore_pos_arg_names=True):
+                        return True
+                    proper_impl_type = get_proper_type(impl_type)
+                    if isinstance(proper_impl_type, CallableType):
+                        if any(
+                            isinstance(get_proper_type(tp), AnyType)
+                            for tp in proper_impl_type.arg_types
+                        ):
+                            return True
         if not is_subtype(override, original, ignore_pos_arg_names=True):
             fail = True
         elif isinstance(override, Overloaded) and self.is_forward_op_method(name):

test-data/unit/check-overloading.test

@@ -1105,6 +1105,31 @@ class B(A):
     def f(self, x: str) -> str: return ''
 [out]
 
+[case testOverloadedMethodWithNarrowerReturnTypes]
+from typing import overload, Union, Optional
+
+class A:
+    def view(self, x: Optional[int] = None) -> "A":
+        ...
+
+class B(A):
+    def view(self, x: Optional[int] = None) -> "B":
+        return B()
+
+class C(A):
+    @overload  # Should be allowed since B is a subtype of A
+    def view(self, x: int) -> B: ...
+    @overload  # Should be allowed since C is a subtype of A
+    def view(self, x: None = None) -> "C": ...
+    def view(self, x: Optional[int] = None) -> Union[B, C]:
+        if x is None:
+            return C()
+        else:
+            return B()
+
+reveal_type(C().view(None))  # N: Revealed type is "__main__.C"
+reveal_type(C().view(5))     # N: Revealed type is "__main__.B"
+
 [case testOverrideOverloadedMethodWithMoreSpecificArgumentTypes]
 from foo import *
 [file foo.pyi]