Relax overload checks to allow return types to be regular subtypes

mypy/checker.py

@@ -3557,7 +3557,7 @@ def is_unsafe_overlapping_signatures(signature: Type, other: Type) -> bool:
             # Special case: all args are subtypes, and returns are subtypes
             if (all(is_proper_subtype(s, o)
                     for (s, o) in zip(signature.arg_types, other.arg_types)) and
-                    is_proper_subtype(signature.ret_type, other.ret_type)):
+                    is_subtype(signature.ret_type, other.ret_type)):
                 return False
             return not is_more_precise_signature(signature, other)
     return True

test-data/unit/check-overloading.test

@@ -1490,3 +1490,17 @@ class Child4(ParentWithDynamicImpl):
 
 [builtins fixtures/tuple.pyi]
 
+[case testOverloadAnyIsConsideredValidReturnSubtype]
+from typing import Any, overload, Optional
+
+@overload
+def foo(x: None) -> Any: ...
+@overload
+def foo(x: Optional[str]) -> str: ...
+def foo(x): pass
+
+@overload
+def bar(x: None) -> object: ...  # E: Overloaded function signatures 1 and 2 overlap with incompatible return types
+@overload
+def bar(x: Optional[str]) -> str: ...
+def bar(x): pass

test-data/unit/lib-stub/attr.pyi

@@ -8,6 +8,20 @@ _ConverterType = Callable[[Any], _T]
 _FilterType = Callable[[Any, Any], bool]
 _ValidatorArgType = Union[_ValidatorType[_T], Sequence[_ValidatorType[_T]]]
 
+# This form catches explicit None or no default but with no other arguments returns Any.
+@overload
+def attrib(default: None = ...,
+           validator: None = ...,
+           repr: bool = ...,
+           cmp: bool = ...,
+           hash: Optional[bool] = ...,
+           init: bool = ...,
+           convert: None = ...,
+           metadata: Optional[Mapping[Any, Any]] = ...,
+           type: None = ...,
+           converter: None = ...,
+           factory: None = ...,
+           ) -> Any: ...
 # This form catches an explicit None or no default and infers the type from the other arguments.
 @overload
 def attrib(default: None = ...,
@@ -36,20 +50,6 @@ def attrib(default: _T,
            converter: Optional[_ConverterType[_T]] = ...,
            factory: Optional[Callable[[], _T]] = ...,
            ) -> _T: ...
-# This form catches explicit None or no default but with no other arguments returns Any.
-@overload
-def attrib(default: None = ...,
-           validator: None = ...,
-           repr: bool = ...,
-           cmp: bool = ...,
-           hash: Optional[bool] = ...,
-           init: bool = ...,
-           convert: None = ...,
-           metadata: Optional[Mapping[Any, Any]] = ...,
-           type: None = ...,
-           converter: None = ...,
-           factory: None = ...,
-           ) -> Any: ...
 # This form covers type=non-Type: e.g. forward references (str), Any
 @overload
 def attrib(default: Optional[_T] = ...,