typing_extension.Self infers the wrong type from __new__

Note: if you are reporting a wrong signature of a function or a class in the standard library, then the typeshed tracker is better suited for this report: https://github.com/python/typeshed/issues.

Describe the bug
When using __new__ directly (example below), the return type is the class itself instead of inferring from the first classmethod param (cls)

To Reproduce

import enum
from typing_extensions import Self, reveal_type


class ActionLevel(enum.IntEnum):
    def __new__(cls, value: int, doc: str) -> Self:
        member = int.__new__(cls, value)
        reveal_type(member)
        member._value_ = value
        member.__doc__ = doc
        return member

Expected behavior
member should be ActionLevel not int

Screenshots or Code

VS Code extension or command-line
Both.
npx pyright@1.1.294 .\scripts\stubsabot.py

Additional context
This was first found here: python/typeshed#9694 (comment)

I'm not able to repro the problem you're seeing. Here's the behavior I see:

Can you confirm that when you paste the above code into a new editor window in a new project with default pyright settings that you get an error?

Perhaps you have an old version of typing_extensions or typing_extensions-stubs installed in your environment?

typing_extensions is 4.5.0
I narrowed down what in the configs causes it: setting "typeshedPath". In this case, my minimal pyrightconfig.json is as such:

{
    "$schema": "https://raw.githubusercontent.com/microsoft/pyright/main/packages/vscode-pyright/schemas/pyrightconfig.schema.json",
    "typeshedPath": ".",
}

I can confirm I have no typing_extensions-stubs in my env:

Note this happens with typing too:
npx pyright@1.1.294 .\scripts\stubsabot.py --pythonversion=3.11

pyright 1.1.294
E:\Users\Avasam\Documents\Git\typeshed\scripts\stubsabot.py
  E:\Users\Avasam\Documents\Git\typeshed\scripts\stubsabot.py:8:21 - information: Type of "member" is "int"
  E:\Users\Avasam\Documents\Git\typeshed\scripts\stubsabot.py:9:16 - error: Cannot assign member "_value_" for type "int"
    Member "_value_" is unknown (reportGeneralTypeIssues)
  E:\Users\Avasam\Documents\Git\typeshed\scripts\stubsabot.py:11:16 - error: Expression of type "int" cannot be assigned to return type "Self@ActionLevel"
    "int" is incompatible with "ActionLevel" (reportGeneralTypeIssues)
2 errors, 0 warnings, 1 information

Is this something that can be fixed on typeshed's side? Or is it due to some special casing done with "typeshedPath" ?

Ah, you're using a version of typeshed that is newer than what is bundled with pyright 1.1.294. That's an important detail! I'm able to repro the problem now, so I'll investigate further.

Fixed bug that resulted in incorrect type evaluation when a `__new__`…

Thanks for the bug report. This will be addressed in the next release.

This is addressed in pyright 1.1.295, which I just published. It will also be included in a future release of pylance.

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`typing_extension.Self` infers the wrong type from `new` #4668

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typing_extension.Self infers the wrong type from __new__ #4668

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erictraut commented on Feb 21, 2023

Avasam commented on Feb 21, 2023

erictraut commented on Feb 21, 2023

erictraut commented on Feb 22, 2023

erictraut commented on Feb 22, 2023

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`typing_extension.Self` infers the wrong type from `new` #4668