Singledispatch return type only tracks base function

[maxrothman]

Python 3.8
Mypy: 7.6.0
issue type: bug

ffrom functools import singledispatch

@singledispatch
def f(arg) -> str:
    pass

@f.register
def _1(arg: int) -> int:
    return arg

@f.register
def _2(arg: list) -> list:
    return list(map(f, arg))

reveal_type(f(1))

Here's the code in the mypy playground

What is the actual behavior/output?

main.py:15: note: Revealed type is 'builtins.str*'

What is the behavior/output you expect?

main.py:15: note: Revealed type is 'builtins.int*'

[ilevkivskyi]

Duplicate of #2904

[LeuschkeTressa]

Note: this is now tracked in #11727.