manual_let_else: do not suggest semantically different replacements

[samueltardieu]

The problem is that this lint does not consider the possibility that the divergent branch can come first and that the patterns may overlap. This led to incorrect suggestions, previously registered as correct in the tests themselves:

let v = match build_enum() {
    _ => continue,
    Variant::Bar(v) | Variant::Baz(v) => v,
};

had a let Variant::Bar(v) | Variant::Baz(v) = v else { continue; } suggestion, which is obviously wrong as the original code continues in any case. Issue #10241 gives another example.

The code now checks that the divergent branch comes second. It could be extended later (I've added a TODO) to check for non-overlapping patterns.

Fixes #10241.

changelog: [manual_let_else] do not suggest non equivalent replacements in match

[rustbot]

r? @dswij

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[samueltardieu]

r? @llogiq

[llogiq]

Thanks, that makes sense.

@bors r+

[bors]

📌 Commit 09d3097 has been approved by llogiq

It is now in the queue for this repository.

[bors]

⌛ Testing commit 09d3097 with merge 6444621...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: llogiq
Pushing 6444621 to master...