Output a warning to stderr when an invalid key is read from an INI config file

[gnikonorov]

Implementation of #6856.
Changes:

• Show a warning when an invalid INI key is read from a config ini file.
• Add the --strict-config which forces warnings to become errors

[gnikonorov]

So now, the output looks like this:

============================================================================================================ 1 passed in 0.02s =============================================================================================================
(.venv) gnikonorov:~/pytest/gleb_test$ python3 -m pytest test_change.py
WARNING: unknown config ini key: superbadkey
=========================================================================================================== test session starts ============================================================================================================
platform linux -- Python 3.6.9, pytest-5.4.1.dev381+geef4f87e7.d20200531, py-1.8.1, pluggy-0.13.1
rootdir: /home/gnikonorov/pytest/gleb_test, inifile: pytest.ini
plugins: hypothesis-5.15.1
collected 1 item

test_change.py .                                                                                                                                                                                                                     [100%]

============================================================================================================ 1 passed in 0.02s =============================================================================================================
(.venv) gnikonorov:~/pytest/gleb_test$

[RonnyPfannschmidt]

thanks for getting this started it's a good idea

the validation call has to happen after all plugins are registered
we might need a additional declaration of required plugins to know all the options or a way to opt out of this for projects that declare options of pytest plugins which are not always installed

[RonnyPfannschmidt]

i wonder if we should use real python warning here and set the file to the configfile/the line to the line of the key

[gnikonorov]

I used sys.stderr becauase it looks like the rest of this file does ( see https://github.com/pytest-dev/pytest/blob/master/src/_pytest/config/__init__.py#L1228 for example ). I don't mind changing it though

[gnikonorov]

sorry @RonnyPfannschmidt I didn't see your review and added in the --strict-config flag the issue requestor mentioned. It's late here, I'll update this PR again tomorrow regarding your comments

[gnikonorov]

@RonnyPfannschmidt - I think I placed the validation after plugin consideration now.
I guess we just need to resolve #7286 (comment) now

[gnikonorov]

Personally, I think we should keep with the file and use sys.stderr for consistency, and maybe open an issue to track refactoring all sys.stderr calls into warning. Thoughts @RonnyPfannschmidt ?

[gnikonorov]

Created a new issue to track the migration to the warnings module. I think this PR is good for another look, @RonnyPfannschmidt

[RonnyPfannschmidt]

Looking good now

The changelog fragments is empty ,
And a second follow up issue we need is the list of the required plugins

[gnikonorov]

Sorry about that @RonnyPfannschmidt, I could have sworn I wrote the change log entry. It's added in now.

I'll create the second follow up issue tonight

[RonnyPfannschmidt]

@gnikonorov it looks like a good old `git add´ before adding content, most of us have been there and review has our backs for that ^^

[gnikonorov]

Most definitely @RonnyPfannschmidt
Does the pipeline not auto merge? Seems like it’s hanging on all green

[RonnyPfannschmidt]

we have no automated merge after green, its easy to miss/fail a detail, so merges are done by hand

[gnikonorov]

That makes sense, thanks for explaining @RonnyPfannschmidt !