Unused section warning with warn_unused_configs and cache

[The-Compiler]

With mypy 0.641 or the latest git master, and a config file like:

[mypy]
warn_unused_configs = True
[mypy-bdb]
ignore_missing_imports = True

checking a file like

import bdb

suppresses the error: No library stub file for standard library module 'bdb' error as expected.

However, when running mypy a second time, I assume results are retrieved from its cache, and it shows:

Warning: unused section(s) in mypy.ini: [mypy-bdb]

which means I can only use --warn-unused-configs selectively (like after editing the config), as otherwise, I'd get a lot of bogus warnings in day-to-day usage.

This is probably somewhat similar to #2960, which is the same kind of issue for --warn-unused-ignores.

[petergaultney]

I see this on 0.700 as well. passing --no-warn-unused-configs does silence the error, but it seems strange, since my

[mypy-boto3]
ignore_missing_imports = True

is definitely doing something.

[jtherrmann]

I'm getting the same problem with 0.701 with these lines in mypy.ini:

[mypy-tests.*]
disallow_untyped_defs = False

They're definitely working, but I still get the Warning: unused section(s) in mypy.ini: [mypy-tests.*] error. This happens regardless of whether .mypy_cache is present.

Though, oddly enough, I'm doing this in two different projects but only getting this problem in one of them. I haven't had time to do further debugging.

[JukkaL]

Increasing priority since this seems to affect quite a few people. I think that I've seen this myself as well.

[gvanrossum]

I can do this. Or we can mark it "easy first issue"?

[JukkaL]

I suspect that this might be a bit difficult for a first issue, at least without a few hints.

[gvanrossum]

I can do a simple version of this: ignore the flag when in incremental mode (which is the default). I'm not sure I'm up to fixing it the way we fixed warn_redundant_casts / warn_unused_ignores.