flake8 #noqa comments get moved a place where they're ignored

[shish]

Operating system: Linux
Python version: 3.6
Black version: 18.4a5
Does also happen on master: ?

Using a long list of typing imports with #noqa because my code is py2 compatible so I'm using the comment syntax for type hints

original code

from typing import Dict, List, Set, ...  # noqa

becomes

from typing import (
    Dict,
    List,
    Set,
    ...,
)  # noqa

but flake8 wants

from typing import (  # noqa
    Dict,
    List,
    Set,
    ...,
)

[zsol]

You can work around this by doing

from typing import (
    Dict,  # noqa
    List,  # noqa
    ...,
)

[ambv]

Shish, Black doesn't understand how noqa comments are different from other comments. Even if it did, that would be a heuristic at best since any part of the bracketed expression may end up on its own line and we don't know which part exactly is meant to be silenced. I'm open to a pull request to improve this but my gut feeling is that it would be pretty tricky to get right. I hope that making the user adapt the reformatted code once so that other linters are happy isn't too much to ask.

What @zsol is suggesting will work, but you can also say what you suggested and Black will keep it:

from typing import (  # noqa
    Dict,
    List,
    Sequence,
    ...
)

[shish]

Yeah, I can see why this would be a very tricky special case - in my own code I manually moved the comment once, and black now keeps it in the correct place; it's just when I did the original one-off bulk-reformat of my project that a bunch of flake8 errors suddenly became un-silenced :)

[JelleZijlstra]

I ran into a similar issue with # type: ignore comments; black moved around my # type: ignores on some long lines, and now mypy no longer likes my code.

[ambv]

@JelleZijlstra, were you able to move # type: ignore back where you wanted it?

[shish]

I wonder if "when reformatting a one-line statement with a comment into a multi-line statement with a comment, put the comment at the end of the first line instead of at the end of the last line" would be a good approach? Running through some examples in my head I think that that should be equally consistent as the current behaviour, but it would Just Work more in more cases (and it feels more intuitive IMO - if I'm commenting a block of code, I put the comment at the start of the block)

[ambv]

I think what I can do for # noqa and # type: ignore is to move the comment after the opening parenthesis instead of after the closing parenthesis (because the latter is guaranteed to have no effect).

[zsol]

Maybe consider handling # pylint: comments as well, as described in #386