Adjustable whitelines feature

[Klavionik]

I've been suffering from the same behavior that was mentioned in several issues:

• yamlfix overly aggressively removes spaces between list items #230
• Option to keep whitelines not just in sections #242

So I decided to give it a try and implement a solution.

What I did was:

1. I found a piece of code that removes our beloved whitelines (namely the _fix_whitelines method) and added a new config option, whitelines, to make it adjustable (right now it just multiplies whitelines by zero, removing them completely).
2. I rewrote _fix_flow_style_lists method so that it not only fixes Ruyaml's bad behavior, but also keeps the whitelines that happened to be inside the flow style list. I also made it run before _fix_whitelines. Then I had to fix test_fix_code_functions_emit_debug_logs as it was comparing lists and broke after I changed the order of fixers (maybe I should've just reorder the expected list?).
3. I slightly fixed _add_newline_at_end_of_file so that it won't add excessive whitelines, only make sure that there's exactly 1 newline at the end of a file.

This is probably not the ideal solution, but I hope it helps to cover some common use cases.

Checklist

• Add test cases to all the changes you introduce
• Update the documentation for the changes

[coveralls]

Pull Request Test Coverage Report for Build 5032706547

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 6 of 6 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.005%) to 99.793%

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Totals
Change from base Build 4881195162:	-0.005%
Covered Lines:	482
Relevant Lines:	483

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💛 - Coveralls

[lyz-code]

Hi @Klavionik thank you so much for your pull request, it is beautiful. You not only fixed one of the most complained issues, but also reduced the complexity of the code and added more comments.

Sorry for taking so long to answer, please take a look at the only comment I've made and we'll be ready to merge it :)

[calumy]

Would you consider adding this to the CLI too, rather than relying on an environment variable? This would be useful when running with pre-commit.

[lyz-code]

By the way this PR will probably solve also this issue #237. Can you please check if it does? If you can't it's fine

[lyz-code]

Would you consider adding this to the CLI too, rather than relying on an environment variable? This would be useful when running with pre-commit.

@calumy can you try to use a config file with the -c flag?

[Klavionik]

By the way this PR will probably solve also this issue #237. Can you please check if it does? If you can't it's fine

This PR indeed solves this problem.

Before:

test: |
  Onetwothree  

  Onetwothree

  Onetwothree

After (with whitelines = 1)

---
test: |-
  Onetwothree  

  Onetwothree

  Onetwothree

[Klavionik]

Thank you! I'm glad to help. Actually 4 days is a pretty fast response, so don't be hard on youself!

I acted upon your review and force-pushed the changes.

[calumy]

Would you consider adding this to the CLI too, rather than relying on an environment variable? This would be useful when running with pre-commit.

@calumy can you try to use a config file with the -c flag?

Apologies for the noise. I forgot that it was possible to configure through a config file. Thanks for highlighting this fact and thanks for the great tool.

[lyz-code]

Thanks for your contribution and kind words ^^

[lyz-code]

Included in 1.10.0