Mypy plugin generates incompatible type overloads for @curry decorated functions with TypeVar

[fadedDexofan]

Bug report

What's wrong

returns mypy plugin generate incorrect type overloads for curry decorated function with TypeVar arguments

Code to reproduce issue:

from typing import TypeVar

from returns.curry import curry
from returns.io import IO

_T = TypeVar('_T', int, str)

@curry
def _union_sets(first_set: set[_T], second_set: set[_T]) -> set[_T]:
    return first_set.union(second_set)

@curry
def _concat_objs(first: _T, second: _T) -> _T:
    return first + second

set_1 = IO({1, 2, 3})
set_2 = IO({3, 4, 5})

union = set_1.apply(set_2.apply(IO(_union_sets)))

string_1 = IO('a')
string_2 = IO('b')

concat = string_1.apply(string_2.apply(IO(_concat_objs)))

Mypy gives incompatible type overloaded function error for both curried functions:

error: Argument 1 to "IO" has incompatible type overloaded function; expected "Callable[[Set[int]], Callable[..., Set[_T]]]"  [arg-type]
error: Argument 1 to "IO" has incompatible type overloaded function; expected "Callable[[Set[int]], Callable[[Set[int]], Set[_T]]]"  [arg-type]
error: Argument 1 to "IO" has incompatible type overloaded function; expected "Callable[[str], Callable[..., _T]]"  [arg-type]
error: Argument 1 to "IO" has incompatible type overloaded function; expected "Callable[[str], Callable[[str], _T]]"  [arg-type]

How is that should be

Type overloads for functions with TypeVar's should be generated correctly

System information

• python version: 3.9.7

• returns version: 0.16.0

• mypy version: 0.910

• hypothesis version (if any):

• pytest version (if any):

[fadedDexofan]

Found that error disappears if add type annotation to result var. E.g.

union: IO[set[int]] = set_1.apply(set_2.apply(IO(_union_sets)))
concat: IO[set[str]] = string_1.apply(string_2.apply(IO(_concat_objs)))