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Fix descriptor access for complex generics #21506

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Fix descriptor access for complex generics #21506

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49213a0
Fix descriptor access for complex generics (fixes #21505)
JiwaniZakir May 18, 2026
9df2b5f
Fix mypy self-check type errors in analyze_descriptor_access
JiwaniZakir May 18, 2026
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24 changes: 13 additions & 11 deletions mypy/checkmember.py
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Original file line number Diff line number Diff line change
Expand Up @@ -710,15 +710,15 @@ def analyze_descriptor_access(descriptor_type: Type, mx: MemberContext) -> Type:
)
return AnyType(TypeOfAny.from_error)

bound_method = analyze_decorator_or_funcbase_access(
defn=dunder_get,
itype=descriptor_type,
name="__get__",
mx=mx.copy_modified(self_type=descriptor_type),
)

typ = map_instance_to_supertype(descriptor_type, dunder_get.info)
dunder_get_type = expand_type_by_instance(bound_method, typ)
# Use the unbound __get__ type and pass (self, instance, owner) together so that
# type inference can jointly solve all type variables. The bound-method approach
# (bind_self first, then call with 2 args) fails when the __get__ self annotation
# contains type variables that appear in the instance parameter too, because
# bind_self may not be able to unify them correctly against complex callable types.
dunder_get_func = dunder_get.func if isinstance(dunder_get, Decorator) else dunder_get
typ = function_type(dunder_get_func, mx.chk.named_type("builtins.function"))
typ_for_instance = map_instance_to_supertype(descriptor_type, dunder_get_func.info)
dunder_get_type: Type = expand_type_by_instance(typ, typ_for_instance)

if isinstance(instance_type, FunctionLike) and instance_type.is_type_obj():
owner_type = instance_type.items[0].ret_type
Expand All @@ -734,21 +734,23 @@ def analyze_descriptor_access(descriptor_type: Type, mx: MemberContext) -> Type:
callable_name,
dunder_get_type,
[
TempNode(orig_descriptor_type, context=mx.context),
TempNode(instance_type, context=mx.context),
TempNode(TypeType.make_normalized(owner_type), context=mx.context),
],
[ARG_POS, ARG_POS],
[ARG_POS, ARG_POS, ARG_POS],
mx.context,
object_type=descriptor_type,
)

_, inferred_dunder_get_type = mx.chk.expr_checker.check_call(
dunder_get_type,
[
TempNode(orig_descriptor_type, context=mx.context),
TempNode(instance_type, context=mx.context),
TempNode(TypeType.make_normalized(owner_type), context=mx.context),
],
[ARG_POS, ARG_POS],
[ARG_POS, ARG_POS, ARG_POS],
mx.context,
object_type=descriptor_type,
callable_name=callable_name,
Expand Down
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