Suggest cfg(false) instead of cfg(FALSE)

[clubby789]

Split from #149791

cc @Urgau

[rustbot]

Some changes occurred in check-cfg diagnostics

cc @Urgau

[rustbot]

r? @madsmtm

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[joshtriplett]

LGTM. r=me once CI passes.

@bors delegate+

[bors]

✌️ @clubby789, you can now approve this pull request!

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[Kivooeo]

This will not work on cases like "False" right?

[clubby789]

That's correct - this is mostly based off of FALSE being a somewhat common idiom, while False is not

[jdonszelmann]

hm, have you seen @scrabsha's work on uppercase/lowercase suggestions in the parser? I think it'd be cool if we could suggest against all mis-capitalizations here and maybe do that in a general enough way that all attribute parsers can benefit from it instead of a cfg-specific lint. At least, could you take a quick look if we can re-use the parsing infra for it? I like it when the error messages are consistent :)

[jdonszelmann]

if that doesn't help let me know and I'll approve this version. The change is a good one.

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[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[jdonszelmann]

@bors delegate-