Properly use proper subtyping for callables (#16343)

Fixes #16338

This is kind of a major change, but it is technically correct: we should
not treat `(*args: Any, **kwargs: Any)` special in `is_proper_subtype()`
(only in `is_subtype()`). Unfortunately, this requires an additional
flag for `is_callable_compatible()`, since currently we are passing the
subtype kind information via a callback, which is not applicable to
handling argument kinds.

Author: ilevkivskyi

mypy/checker.py

@@ -800,7 +800,7 @@ def check_overlapping_overloads(self, defn: OverloadedFuncDef) -> None:
 
                 # Is the overload alternative's arguments subtypes of the implementation's?
                 if not is_callable_compatible(
-                    impl, sig1, is_compat=is_subtype, ignore_return=True
+                    impl, sig1, is_compat=is_subtype, is_proper_subtype=False, ignore_return=True
                 ):
                     self.msg.overloaded_signatures_arg_specific(i + 1, defn.impl)
 
@@ -7685,6 +7685,7 @@ def is_unsafe_overlapping_overload_signatures(
         signature,
         other,
         is_compat=is_overlapping_types_no_promote_no_uninhabited_no_none,
+        is_proper_subtype=False,
         is_compat_return=lambda l, r: not is_subtype_no_promote(l, r),
         ignore_return=False,
         check_args_covariantly=True,
@@ -7694,6 +7695,7 @@ def is_unsafe_overlapping_overload_signatures(
         other,
         signature,
         is_compat=is_overlapping_types_no_promote_no_uninhabited_no_none,
+        is_proper_subtype=False,
         is_compat_return=lambda l, r: not is_subtype_no_promote(r, l),
         ignore_return=False,
         check_args_covariantly=False,
@@ -7744,7 +7746,7 @@ def overload_can_never_match(signature: CallableType, other: CallableType) -> bo
         signature, {tvar.id: erase_def_to_union_or_bound(tvar) for tvar in signature.variables}
     )
     return is_callable_compatible(
-        exp_signature, other, is_compat=is_more_precise, ignore_return=True
+        exp_signature, other, is_compat=is_more_precise, is_proper_subtype=True, ignore_return=True
     )
 
 
@@ -7754,7 +7756,9 @@ def is_more_general_arg_prefix(t: FunctionLike, s: FunctionLike) -> bool:
     #      general than one with fewer items (or just one item)?
     if isinstance(t, CallableType):
         if isinstance(s, CallableType):
-            return is_callable_compatible(t, s, is_compat=is_proper_subtype, ignore_return=True)
+            return is_callable_compatible(
+                t, s, is_compat=is_proper_subtype, is_proper_subtype=True, ignore_return=True
+            )
     elif isinstance(t, FunctionLike):
         if isinstance(s, FunctionLike):
             if len(t.items) == len(s.items):
@@ -7769,6 +7773,7 @@ def is_same_arg_prefix(t: CallableType, s: CallableType) -> bool:
         t,
         s,
         is_compat=is_same_type,
+        is_proper_subtype=True,
         ignore_return=True,
         check_args_covariantly=True,
         ignore_pos_arg_names=True,

mypy/constraints.py

@@ -1352,7 +1352,11 @@ def find_matching_overload_item(overloaded: Overloaded, template: CallableType)
         # Return type may be indeterminate in the template, so ignore it when performing a
         # subtype check.
         if mypy.subtypes.is_callable_compatible(
-            item, template, is_compat=mypy.subtypes.is_subtype, ignore_return=True
+            item,
+            template,
+            is_compat=mypy.subtypes.is_subtype,
+            is_proper_subtype=False,
+            ignore_return=True,
         ):
             return item
     # Fall back to the first item if we can't find a match. This is totally arbitrary --
@@ -1370,7 +1374,11 @@ def find_matching_overload_items(
         # Return type may be indeterminate in the template, so ignore it when performing a
         # subtype check.
         if mypy.subtypes.is_callable_compatible(
-            item, template, is_compat=mypy.subtypes.is_subtype, ignore_return=True
+            item,
+            template,
+            is_compat=mypy.subtypes.is_subtype,
+            is_proper_subtype=False,
+            ignore_return=True,
         ):
             res.append(item)
     if not res:

mypy/meet.py

@@ -462,6 +462,7 @@ def _type_object_overlap(left: Type, right: Type) -> bool:
             left,
             right,
             is_compat=_is_overlapping_types,
+            is_proper_subtype=False,
             ignore_pos_arg_names=True,
             allow_partial_overlap=True,
         )

mypy/subtypes.py

@@ -658,6 +658,8 @@ def visit_parameters(self, left: Parameters) -> bool:
                 left,
                 self.right,
                 is_compat=self._is_subtype,
+                # TODO: this should pass the current value, but then couple tests fail.
+                is_proper_subtype=False,
                 ignore_pos_arg_names=self.subtype_context.ignore_pos_arg_names,
             )
         else:
@@ -677,6 +679,7 @@ def visit_callable_type(self, left: CallableType) -> bool:
                 left,
                 right,
                 is_compat=self._is_subtype,
+                is_proper_subtype=self.proper_subtype,
                 ignore_pos_arg_names=self.subtype_context.ignore_pos_arg_names,
                 strict_concatenate=(self.options.extra_checks or self.options.strict_concatenate)
                 if self.options
@@ -932,6 +935,7 @@ def visit_overloaded(self, left: Overloaded) -> bool:
                                 left_item,
                                 right_item,
                                 is_compat=self._is_subtype,
+                                is_proper_subtype=self.proper_subtype,
                                 ignore_return=True,
                                 ignore_pos_arg_names=self.subtype_context.ignore_pos_arg_names,
                                 strict_concatenate=strict_concat,
@@ -940,6 +944,7 @@ def visit_overloaded(self, left: Overloaded) -> bool:
                                 right_item,
                                 left_item,
                                 is_compat=self._is_subtype,
+                                is_proper_subtype=self.proper_subtype,
                                 ignore_return=True,
                                 ignore_pos_arg_names=self.subtype_context.ignore_pos_arg_names,
                                 strict_concatenate=strict_concat,
@@ -1358,6 +1363,7 @@ def is_callable_compatible(
     right: CallableType,
     *,
     is_compat: Callable[[Type, Type], bool],
+    is_proper_subtype: bool,
     is_compat_return: Callable[[Type, Type], bool] | None = None,
     ignore_return: bool = False,
     ignore_pos_arg_names: bool = False,
@@ -1517,6 +1523,7 @@ def g(x: int) -> int: ...
         left,
         right,
         is_compat=is_compat,
+        is_proper_subtype=is_proper_subtype,
         ignore_pos_arg_names=ignore_pos_arg_names,
         allow_partial_overlap=allow_partial_overlap,
         strict_concatenate_check=strict_concatenate_check,
@@ -1552,12 +1559,13 @@ def are_parameters_compatible(
     right: Parameters | NormalizedCallableType,
     *,
     is_compat: Callable[[Type, Type], bool],
+    is_proper_subtype: bool,
     ignore_pos_arg_names: bool = False,
     allow_partial_overlap: bool = False,
     strict_concatenate_check: bool = False,
 ) -> bool:
     """Helper function for is_callable_compatible, used for Parameter compatibility"""
-    if right.is_ellipsis_args:
+    if right.is_ellipsis_args and not is_proper_subtype:
         return True
 
     left_star = left.var_arg()
@@ -1566,9 +1574,9 @@ def are_parameters_compatible(
     right_star2 = right.kw_arg()
 
     # Treat "def _(*a: Any, **kw: Any) -> X" similarly to "Callable[..., X]"
-    if are_trivial_parameters(right):
+    if are_trivial_parameters(right) and not is_proper_subtype:
         return True
-    trivial_suffix = is_trivial_suffix(right)
+    trivial_suffix = is_trivial_suffix(right) and not is_proper_subtype
 
     # Match up corresponding arguments and check them for compatibility. In
     # every pair (argL, argR) of corresponding arguments from L and R, argL must

test-data/unit/check-overloading.test

@@ -6501,7 +6501,7 @@ eggs = lambda: 'eggs'
 reveal_type(func(eggs))  # N: Revealed type is "def (builtins.str) -> builtins.str"
 
 spam: Callable[..., str] = lambda x, y: 'baz'
-reveal_type(func(spam))  # N: Revealed type is "def (*Any, **Any) -> builtins.str"
+reveal_type(func(spam))  # N: Revealed type is "def (*Any, **Any) -> Any"
 [builtins fixtures/paramspec.pyi]
 
 [case testGenericOverloadOverlapWithType]
@@ -6673,3 +6673,23 @@ c2 = MyCallable("test")
 reveal_type(c2)  # N: Revealed type is "__main__.MyCallable[builtins.str]"
 reveal_type(c2()) # should be int  # N: Revealed type is "builtins.int"
 [builtins fixtures/tuple.pyi]
+
+[case testOverloadWithStarAnyFallback]
+from typing import overload, Any
+
+class A:
+    @overload
+    def f(self, e: str) -> str: ...
+    @overload
+    def f(self, *args: Any, **kwargs: Any) -> Any: ...
+    def f(self, *args, **kwargs):
+        pass
+
+class B:
+    @overload
+    def f(self, e: str, **kwargs: Any) -> str: ...
+    @overload
+    def f(self, *args: Any, **kwargs: Any) -> Any: ...
+    def f(self, *args, **kwargs):
+        pass
+[builtins fixtures/tuple.pyi]