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dataclass_transform decorator not detected when using alias #19731
Description
Bug Report
I came across this while trying to conditionally use typing.dataclass_transform or typing_extensions.dataclass_transforms depending on the Python version running the code.
If one defines an alias for dataclass_transform, using the alias as a decorator does not result in the expected result (mypy does not recognize the decorated class as if being decorated with dataclass_transform)
To Reproduce
Playground link: https://mypy-play.net/?mypy=latest&python=3.12&gist=c88ba0d811ade24ad47f302dfdb5b6f7
import dataclasses
import typing
dataclass_transform = typing.dataclass_transform
@dataclass_transform()
def transform(cls, /, **kwargs):
return dataclasses.dataclass(**kwargs)
@transform
class Example:
field: int
Example(field=1)Expected Behavior
No error, same as if typing.dataclass_transform was being used directly
Actual Behavior
Example is not recognized as a dataclass-like class:
main.py:17: error: Unexpected keyword argument "field" for "Example" [call-arg]
Your Environment
- Mypy version used: 1.17.1
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): none - Python version used: 3.12
Activity
sterliakov commentedon Aug 27, 2025
There are multiple hardcoded fullnames in mypy that do not support aliasing. The same applies to
typing.no_type_checkandtyping.TypedDict, for example.https://mypy-play.net/?mypy=master&python=3.10&flags=strict&gist=e75986dae521c8386ff818e57e79ad40
Apparently
dataclasses.dataclasscan't be aliased either.alex commentedon Sep 1, 2025
Is this a fundamental limitation of mypy's design, or just an incidental limitation for how these APIs were implemented?
sterliakov commentedon Sep 1, 2025
It's an implementation issue AFAIC. Maybe I'll try to get it working this week, there are multiple tickets caused by this.
alex commentedon Sep 1, 2025
Thanks!