New lint: result-unit-err

[llogiq]

This fixes #1721.

• Followed lint naming conventions
• Added passing UI tests (including committed .stderr file)
• cargo test passes locally
• Executed cargo dev update_lints
• Added lint documentation
• Run cargo dev fmt

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changelog: new lint: result-unit-err

[rust-highfive]

r? @ebroto

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[ebroto]

Left some thoughts.

I'm a bit hesitant about making it warn-by-default, beause I'm sure we are going to hear opinions on this :) but I would say that since it's warning only on public functions, it's more than desirable to not use this pattern there.

[llogiq]

Yeah, I was thinking about making it allow by default, but then it's only for the public interface, and missing the Error trait here is usually bad style. Non-newbies will find the lint to be easy to allow anyway. Perhaps I should add a check for no_std code where a Result<_, ()> is somewhat more likely to be acceptable?

Otherwise r?

[ebroto]

Perhaps I should add a check for no_std code where a Result<_, ()> is somewhat more likely to be acceptable

I think that's a good idea, but given that we lint only on () I think we can assume no_std users can use another type.

I did not see a nit before (error messages shouldn't be capitalized), I've changed it myself. When CI passes I'll merge this, thank you!

[ebroto]

@bors r+

[bors]

📌 Commit 74ae116 has been approved by ebroto

[bors]

⌛ Testing commit 74ae116 with merge 92783e3...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: ebroto
Pushing 92783e3 to master...