fix: improve error messaging for unreachable loop return cases

[yossydev]

Check to see if the pattern is single binding, and if so, display a better error message!

ref: #116572

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @b-naber (or someone else) soon.

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[yossydev]

@rustbot review

[fmease]

Could you please add a test for this in tests/ui?

[yossydev]

Could you please add a test for this in tests/ui?

ok!

[fmease]

r? fmease

[Dylan-DPC]

@yossydev any updates on adding the test? thanks

[yossydev]

@Dylan-DPC

any updates on adding the test? thanks

We are currently making it! Is it possible to wait a little longer...?

[Dylan-DPC]

@yossydev sure take your time, just wanted to check if you were still working on it or if there some issue that we can help resolve. Thanks

[fmease]

@yossydev I'd say enough time has passed, I'll close this PR due to inactivity.

Feel to free to open a new PR once you find the time to work on this again. You can also ping me if and before you'd like to push your changes to this PR since I think I need to reopen it for you (?).

Note that the next time around it would be great if you could add some sort of UI test as well as a short explainer how the changes relate to issue #116572 (if it works towards fixing it, if it fixes it completely, ...).

You can consult the rustc dev guide on writing UI tests and a lot of other things.