"An implementation for an overloaded function is not allowed in a stub file" for overloaded type hint

Bug Report

I'm documenting a compiled extension module written in Rust. I write docstrings in my .pyi file so that IDEs and API documentation can automatically pick up those docstrings.

Docstrings are allowed in functions but this errors when a function is overloaded.

To Reproduce

# tmp.pyi

from typing import overload

def fn1() -> None:
    """Call this function."""

@overload
def fn2(a: str) -> str: ...
@overload
def fn2(a: int) -> int: ...
def fn2(a: int | str) -> int | str:
    """Call this function."""

uv run mypy tmp.pyi

gives:

tmp.pyi:10: error: An implementation for an overloaded function is not allowed in a stub file  [misc]

Note that this does not error on line 3 for the non-overloaded function.

Expected Behavior

Expected mypy to not error when a docstring is included on a function that has overloads.

Actual Behavior

tmp.pyi:10: error: An implementation for an overloaded function is not allowed in a stub file  [misc]
Found 1 error in 1 file (checked 1 source file)

Your Environment

• Mypy version used:

  > uv run mypy --version
  mypy 1.15.0 (compiled: yes)
  

• Mypy command-line flags: None, just uv run mypy tmp.pyi

• Mypy configuration options from mypy.ini (and other config files): None

• Python version used:

  > uv run python --version
  Python 3.9.21
  

Inizia eseguendo uv run mypy tmp.pyi con il riproduttore e segui la diagnostica riportata alla riga 10 per la funzione stub sovraccaricata. Aggiungi una copertura di regressione per consentire il suo docstring e conferma che il comando termini senza questo errore.