Click option value type incorrect if `multiple=True`.

[adamtheturtle]

Install dependencies:

$ pip install click mypy
$ mypy --version
mypy 0.641
$

Create example.py:

from typing import Sequence, Union

import click

def my_callback(
    ctx: click.core.Context,
    param: Union[click.core.Option, click.core.Parameter],
    value: Sequence[Union[int, bool, str]],
):
    print('Value is: ' + str(value))

@click.command('example')
@click.option('-x', multiple=True, callback=my_callback)
def example(x):
    pass

if __name__ == '__main__':
    example()

Run this to see that value is a tuple:

$ python example.py
Value is: ()
$

Run mypy which incorrectly tells us that value must be Union[bool, int, str]:

$ mypy example.py
example.py:13: error: Argument "callback" to "option" has incompatible type "Callable[[Context, Union[Option, Parameter], Sequence[Union[int, bool, str]]], Any]"; expected "Optional[Callable[[Context, Union[Option, Parameter], Union[bool, int, str]], Any]]"

[srittau]

The best option is probably to just change the type of the value argument to Any in the definition of Callback:

typeshed/third_party/2and3/click/decorators.pyi

Lines 12 to 15 in 59040f0

	_Callback = Callable[
	[Context, Union[Option, Parameter], Union[bool, int, str]],
	Any
	]