python / python/mypy

overloads in `if TYPE_CHECKING` shouldn't require implementations

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#19,169 3 comments 0 reactions 0 assignees View on GitHub

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feature topic-overloads
Dominant language
Python
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Description

Feature

As I explained in the title.

Pitch

Currently this raises an error:

from typing import TYPE_CHECKING, overload

if TYPE_CHECKING:
    @overload  # E: An overloaded function outside a stub file must have an implementation
    def f(x: int) -> str:
        ...
    
    @overload
    def f(x: str) -> bytes:
        ...

I think that if code is in if TYPE_CHECKING then it shouldn't need an implementation though.

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First steps

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Research direction

Start by reproducing the diagnostic with the provided TYPE_CHECKING and overload snippet, then trace the type-checking path that reports the missing implementation. Done means overloads inside TYPE_CHECKING are accepted without an implementation while the existing requirement remains for ordinary Python code.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers, devtools
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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