overload + decorator to transform callable into class protocol w/ attribute does not see the attribute
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Description
Bug Report
Trying to combine function attributes (a la #2087) where we add the attribute with a decorator fails to apply the decorator and the attribute is dropped on the ground.
To Reproduce
from __future__ import annotations
from typing import overload, Callable, TypeVar, Protocol
from typing_extensions import ParamSpec, reveal_type
P = ParamSpec("P")
R = TypeVar("R", covariant=True)
class WithExtra(Protocol[P, R]):
extra: str
def __call__(self, *args: P.args, **kwargs: P.kwargs) -> R: ...
def add_extra(func: Callable[P, R]) -> WithExtra[P, R]:
func.extra = "added" # type: ignore
return func # type: ignore
@overload
@add_extra
def foo(x: int) -> str: ...
@overload
@add_extra
def foo(x: str) -> str: ...
@add_extra
def foo(x: int | str) -> str:
return str(x)
assert foo.extra # type: ignore[attr-defined]
reveal_type(foo) # Revealed type is "Overload(def (x: builtins.int) -> builtins.str, def (x: builtins.str) -> builtins.str)"
This works in pyright.
I feel like it should be possible to work around it with a callable class, but I've yet to figure out the proper incantation.
Real-life use: https://github.com/pytest-dev/pytest/blob/b0caf3d7adc45f773177424593431869fd2f82d8/src/_pytest/python_api.py#L1025
Your Environment
- Mypy version used: 1.14.1
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: python 3.13.1
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running the supplied reproduction with mypy 1.14.1 and verify the revealed overload type and missing extra attribute. Trace the overload and decorator type-analysis paths to identify where the callable protocol information is lost, then add a regression test showing the expected attribute-aware result.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100