False positive in return type on a decorator factory whose results can decorate functions or coroutines
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Description
Bug Report
Mypy gives a false positive (with printed error messages indicating that matching types don't match) on the following code:
from typing import Callable, TypeVar, Coroutine, Any, Union, cast
import asyncio
import functools
import time
F = TypeVar('F', bound=Union[Callable[..., Any], Callable[..., Coroutine[Any, Any, Any]]])
def retry_forever() -> Callable[[F], F]:
"""This function returns a decorator which causes the decorated function or coroutine to
retry repeatedly
:returns: A decorator
"""
def __decorator(f: F) -> F:
if asyncio.iscoroutinefunction(f):
@functools.wraps(f)
async def __inner(*args, **kwargs) -> Any:
while True:
try:
f(*args, **kwargs)
except Exception:
await asyncio.sleep(1)
else:
break
return __inner # error: Incompatible return value type (got "Callable[[VarArg(Any), KwArg(Any)], Coroutine[Any, Any, Any]]", expected "F") [return-value]
else:
@functools.wraps(f)
def __inner(*args, **kwargs) -> Any:
while True:
try:
f(*args, **kwargs)
except Exception:
time.sleep(1)
else:
break
return __inner # error: Incompatible return value type (got "Callable[[VarArg(Any), KwArg(Any)], Coroutine[Any, Any, Any]]", expected "F") [return-value]
return __decorator
To Reproduce
https://mypy-play.net/?mypy=latest&python=3.10&gist=2819b5f48c59c1dde77fc502f34a023c
Expected Behavior
Since the error message reports types which match (modulo the mypy documentation here) this should pass type checking
Your Environment
- Mypy version used: 1.0.0
- Mypy command-line flags: None
- Python version used: 3.10
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 with the provided mypy-play reproducer and inspect the decorator return-value checking path for generic callables that may wrap functions or coroutines. Add a regression test for the shown snippet, then run the relevant type-checking tests; done means the matching return types no longer produce a false positive.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers, devtools
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100