[MRG][feature] Change warns signature to mimic the raises call

[massich]

fixes #2708 providing warns with message and match parameters (similarly to pytest.raises. see #2227)

[massich]

@nicoddemus Before diving into the code, I would like to get some feedback with the functionality itself. Could you check the tests I've written and ping to the appropriated developers to provide feedback before writing the actual feature. Maybe you guys have different view of the problem (like what you pointed in #2708)

[RonnyPfannschmidt]

warns should not replicate the old call style , and even more so for the execute code snippets style, its just an accident of history we should stay clear of

[massich]

so, warnings should always be used within a context manager?

[massich]

I've changed test_message_using in favor of test_message. (The using was a copy-paste error)

[nicoddemus]

Hi @massich sorry for not responding earlier, this one fell through the cracks.

The tests look good to me. The question of whatever we should match a single warning or error out vs match any of the warnings, I think the second is more practical so I would go for it.

I definitely agree we should support only the context manager case and treat function-form and (specially) string-eval forms as history.

cc @flub @hpk42 @The-Compiler would you guys like to share your opinions here?

[The-Compiler]

I don't really have an opinion on this, FWIW - I treat all warnings as errors 😉

[massich]

I got test_match_regex working and I broke some other test, but these could be adressed afterwards. Could you give me some feedback regarding the functionality implementation. cc:@nicoddemus

[flub]

Hi, tests seem fine but I do t see any for the message kwarg. Should that not have been included according to the description?

[massich]

@flub here warns is called with match=r'must be \d+$'

[coveralls]

Coverage decreased (-0.06%) to 92.063% when pulling 8a77dfa on massich:mimic_raises_signature_in_warns into 9d373d8 on pytest-dev:features.

[nicoddemus]

This is looking great!

This needs some docs and a changelog entry, aside my other minor comments.

[nicoddemus]

Please include a case which matches with match but the warning raised is wrong:

with pytest.raises(pytest.fail.Exception):
   with pytest.warns(UserWarning, match=r'must be \d+$'):
       warnings.warn("value must be 42", RuntimeWarning)

[massich]

done.

[nicoddemus]

This is minor, but you are shadowing the builtin compile. I suggest changing to re.compile and import re instead.

[coveralls]

Coverage increased (+0.009%) to 92.057% when pulling aa6a670 on massich:mimic_raises_signature_in_warns into b55a4f8 on pytest-dev:features.

[massich]

The changelog of the feature branch is outdated. Souldn't it have a 3.3.0 section?
Could you update it so that I can rebase feature, or point out where should we state this feature in the changelog

[RonnyPfannschmidt]

@massich we use towncrier to stop the merge pain - please add a news fragment file in the changelog folder

[massich]

Woo thats cool. Thanks.

[coveralls]

Coverage increased (+0.009%) to 92.057% when pulling 80d1654 on massich:mimic_raises_signature_in_warns into b55a4f8 on pytest-dev:features.

[coveralls]

Coverage increased (+0.009%) to 92.057% when pulling a0c6758 on massich:mimic_raises_signature_in_warns into b55a4f8 on pytest-dev:features.

[RonnyPfannschmidt]

well done, thanks 👍