Add wildcard_let lint

[lolbinarycat]

Fixes #4090

changelog: [wildcard_let]: new restriction lint to forbid use of let _

[rustbot]

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[y21]

Is this use-case not already covered by let_underscore_must_use?

[lolbinarycat]

in the 5 years of #4090 being open, noone brought that lint up.

[llogiq]

So I understand there is some overlap, but the wildcard_let lint is broader in scope, correct? In that case, the lint should at least check if the let_underscore_must_use lint would apply and avoid linting in that case to avoid double messages.

[bors]

☔ The latest upstream changes (presumably #12849) made this pull request unmergeable. Please resolve the merge conflicts.

[xFrednet]

Hey @lolbinarycat , this is a ping from triage, since there hasn't been any activity in some time. Are you still planning to continue this implementation?

If you have any questions, you're always welcome to ask them in this PR or on Zulip.

@rustbot author

[lolbinarycat]

@xFrednet not really, since the previously mentioned lint already covers it's usecase.