Bundle LCOV, Cobertura, and SARIF formatters

[sferik]

We absorbed simplecov-html and simplecov_json_formatter into the gem. The three formats that downstream tools actually consume are still third-party gems.

• LCOV is the lingua franca. Coveralls, Codecov, genhtml, and the Coverage Gutters extension for VS Code all read it.
• Cobertura XML is what Jenkins, GitLab, and Azure Pipelines ingest.
• SARIF puts uncovered lines into GitHub code scanning, which is how they get annotated on the diff without a bot account posting comments.

Each one is a few hundred lines against SourceFile and a fixture-based spec, and each replaces a dependency that projects carry for no reason other than getting their numbers into a service. Bundling them also means the formats stay correct when the resultset shape changes, which is not true of a formatter gem that nobody has touched since branch coverage landed.

The related cheap win is --annotate github on simplecov uncovered, emitting ::warning file=lib/foo.rb,line=41::Line not covered. That gets inline diff annotations in a plain workflow with no upload step and no code scanning permissions.

Prior art for bundling rather than farming out: go tool cover writes its own profile format and coverage.py ships xml, lcov, json, and html in the box.

[sferik]

@fortissimo1997, @t-mario-y, @jessebs Curious what you all think about building-in your gems?

SimpleCov recently absorbed the simplecov-html and simplecov_json_formatter gems, which I think was a good decision. Your gems are sufficiently popular (50+ million downloads) that I’d consider including them as well, so these formatters track internal changes the moment they happen instead of waiting on a cross-gem release.

I’d happy add you as maintainers of SimpleCov, so you could continue to work on these features (or not), as well as add core features that your respective formatters could build upon (or not). Just as valuable would be your opinions: output details that downstream consumers are picky about, compatibility quirks you've had to accommodate (Coveralls vs Codecov vs genhtml for LCOV, GitLab vs Jenkins for Cobertura), or anything else you learned maintaining these.

Or you can try to talk me out of this if you think it’s a bad idea. 😊

[sferik]

@chetan I’d also consider folding in simplecov-console if you’re open to it. It doesn’t have quite as many downloads as the others, but “Console” feels like a core format to me and I’d be happy to have you as a co-maintainer.

[jessebs]

@sferik - I'd be willing to have the discussion. Can you provide a way for me to contact you with some questions?

[sferik]

You can ask questions here or email me privately: sferik@gmail.com