Figure out how to detect unused imports

[JukkaL]

Linters like flake8 can detect unused imports, but this actually doesn't work with PEP 484 compliant code, as some of the uses can be in comments that are not seen by the linter. For example:

from typing import List   # 'List' imported but unused 
x = []  # type: List[int]

We should either try to get linters fixed (file issues) or allow mypy to detect these kinds of errors reliably.

[o11c]

Not just unused imports, but all unused variables (that do not start with _).

I think it's best to make mypy do this, controlled via a -W option. But rewriting the parser is going slower than I expected, I keep restarting when I see a better way ...

Related: #465

[pradyunsg]

What needs to be done to help move this forward?

[ilevkivskyi]

What needs to be done to help move this forward?

Make a PR (assuming you are confident enough, since this might be not a small change).

[ilevkivskyi]

(Btw, latest versions of popular linters already understand/will soon understand type comments).

[pradyunsg]

Make a PR (assuming you are confident enough, since this might be not a small change).

Any pointers for where to get started on this?

(Btw, latest versions of popular linters already understand/will soon understand type comments).

Oh, is this due to the work on typed-ast, which would get adopted by the linters?

[gvanrossum]

Please ask a more specific question. Have you read the documentation, have you tried something, what couldn't you get to work?

[emmatyping]

I believe linters now can detect PEP 484 type comments without issue (see e.g. PyCQA/pyflakes#400), so I think we can close this?

[jdahlin]

Would be nice if mypy could support this, its one less tool is needed to lint a code base.

This doesn't seem possible with the current plugin API, perhaps extending the plugin API to expose enough information to make this possible in third-party code would be good enough.