Suggest collapsing nested or patterns if the MSRV allows it

[y21]

Nested or patterns have been stable since 1.53, so we should be able to suggest Some(1 | 2) if the MSRV isn't set below that.

This change adds an msrv check and also moves it to matches/mod.rs, because it's also needed by redundant_guards.

changelog: [collapsible_match]: suggest collapsing nested or patterns if the MSRV allows it

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[y21]

This didn't look right. It seems like the intention was to catch if matches!, but because of the way it was written it would still emit a warning on a manually written match that happens to have the same pattern structure but does something in the _ => ... arm that's semantically different. Changed it to look for the matches! macro and added a test case for a false positive that this fixes.

[y21]

Also one thing I've noticed, these two lints redundant_guards and collapsible_match have a lot in common but unfortunately collapsible_match looks for far fewer patterns. I think it'd be neat if they could catch the same patterns by sharing the code and that collapsible_match would catch

if let Some(v) = Some(42) {
  if v == 42 {}
}

and suggest if let Some(42), just like how redundant_guards does it. I'll try to look into that.

[llogiq]

Agreed, unifying those lints will improve functionality and performance. I'll look forward to a follow-up PR. This one already looks merge-worthy, so thank you for improving clippy!

@bors r+

[bors]

📌 Commit 790fb93 has been approved by llogiq

It is now in the queue for this repository.

[bors]

⌛ Testing commit 790fb93 with merge 20b085d...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing 20b085d to master...