Bug with `type: ignore` comment on import and incremental

[refi64]

Still trying to get a test case. However, for now, I'll post the interesting parts:

• In errors.py, I have code like this:

import colorama  # type: ignore

For some reason, the cache for this file at some point didn't add colorama to the suppressed section, so the import started being an error.

[gvanrossum]

Hm, interesting. @Michael0x2a might have some insights.

[refi64]

Create the following files:

• x.py:

  A = 0
  from y import B

• y.py:

  import xyz  # type: ignore
  B = 0
  from x import A

Now, watch the following commands:

ryan@DevPC-LX ~/blaze-mypy/bug master $ mypy -i x.py  # Works.
ryan@DevPC-LX ~/blaze-mypy/bug master $ touch x.py    # Update the mtime of x.py.
ryan@DevPC-LX ~/blaze-mypy/bug master $ mypy -i x.py  # Works.
ryan@DevPC-LX ~/blaze-mypy/bug master $ touch x.py    # Update the mtime of x.py again.
ryan@DevPC-LX ~/blaze-mypy/bug master $ mypy -i x.py  # Fails!
x.py:2: note: In module imported here:
y.py:1: error: Cannot find module named 'xyz'
y.py:1: note: (Perhaps setting MYPYPATH or using the "--silent-imports" flag would help)
ryan@DevPC-LX ~/blaze-mypy/bug master $ 

[refi64]

Workaround to avoid having to clear the entire cache: rm .mypy_cache/*/y.*.json, replacing y with the module that had the type: ignore comment.

[gvanrossum]

Workarounds for incremental mode that requires deleting cache files are not very useful. :-)

[refi64]

Well, I actually just realized that a much, much better workaround is to just do touch y.py... I don't know why I didn't think of that before...

[gvanrossum]

But it definitely is a bug.

[gvanrossum]

Is this still reproducible?

[refi64]

@gvanrossum Yup.