New lint [four_forward_slashes]

[Centri3]

Closes #9212

changelog: New lint [four_forward_slashes]

[rustbot]

r? @xFrednet

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[xFrednet]

r$ @blyxyas

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[blyxyas]

I cannot stop thinking about rustc_ast::util::comments::gather_comments, it returns a Vec<Comment> and that could be used to check if the comment starts with // or //// (I'm not sure Comment also includes the initial //).

It would be simpler, but we'd have to do a benchmark to verify speed. Maybe SPEEDTEST can help with that?

[Centri3]

gather_comments may work, but from what I can see it'd do a lot more work for the same result. Even just allocating an empty Vec, then increasing its capacity every time a comment is found, would be slow.

Perhaps we can use the lexer though. I hadn't thought to and that may be nicer

[Centri3]

Unfortunately gather_comments won't work. It doesn't give the span of the comment, only the column it starts at (Comment.pos).

[blyxyas]

LGTM, Thanks! ❤️
cc @xFrednet

[xFrednet]

I'm sadly busy until Tuesday/Wednesday, but then I'll do the last check. :)

[xFrednet]

I have full trust in your review:

@bors r=blyxyas

[bors]

📌 Commit 2e43d0c has been approved by blyxyas

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2e43d0c with merge 9f0cbfd...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: blyxyas
Pushing 9f0cbfd to master...