Multiple output-format support

[RuRo]

Steps

• Add yourself to CONTRIBUTORS if you are a new contributor.
• Add a ChangeLog entry describing what your PR does.
• If it's a new feature or an important bug fix, add a What's New entry in doc/whatsnew/<current release.rst>.
• Write a good description on what the PR does.

Description

This PR allows users to specify more than one output format by passing a comma-separated list output-format like this:

--output-format=text,json

You can also set the output file for each output format by specifying it after a colon like this:

--output-format=text:path/to/pylint-report.txt,json:different/path/to/pylint-report.json

Without the :path part, the default is to output to stdout.

Type of Changes

	Type
✓	✨ New feature

Related Issue

Closes #1798

[Pierre-Sassoulas]

Thank you for this merge request. I made some comment to address before merging but I also think we'll need more tests than that, I did not check in detail but I don't think a lot of test cases are tested right now.

[coveralls]

Coverage increased (+0.08%) to 91.803% when pulling 399d0d3 on RuRo:feature/multi-output-formats into 5ebbc30 on PyCQA:master.

[RuRo]

@Pierre-Sassoulas done, I think. Regarding type hints, I've tried my best, but I may need some help with the following:

• I can't annotate the linter property on MultiReporter, because attempting to import pylint/lint/pylinter.py in pylint/reporters/multi_reporter.py leads to circular import errors. I've annotated it with PyLinter = Any for now.
• I don't know the properly parametrized types of stats and previous_stats arguments of MultiReporter.on_close. They seem to be dicts of some kind, so I've annotated them as Mapping[Any, Any] for now.

[RuRo]

I also think we'll need more tests than that, I did not check in detail but I don't think a lot of test cases are tested right now.

Well, there weren't a lot of tests for output-format in the first place.
Feel free to suggest any additional tests that you would like me to write.

[RuRo]

@Pierre-Sassoulas I think I've addressed all the requested changes and all the checks pass now.

[Pierre-Sassoulas]

Thank you for this new option and for adding tests in what was not previously covered. Congratulation on becoming a pylint contributor :)

[RuRo]

Btw, while I have your attention. Do you know, what will the next pylint version be (2.9 or 3.0) and when can we expect its release? The ChangeLogs say 2.9, but PyPI already has some alpha 3.0.0 releases.

[Pierre-Sassoulas]

Pylint 2.9.0 will release very soon (after astroid 2.5.7), pylint 3.0.0alpha is a version including breaking changes (See #3504) that is not going out of alpha before a long time, 3.0.0a4 will release at the same time than 2.9.0.