match_same_arms fix

[Jarcho]

fixes #860
fixes #1140

changelog: Don't lint match_same_arms when an interposing arm's pattern would overlap

[rust-highfive]

r? @xFrednet

(rust-highfive has picked a reviewer for you, use r? to override)

[camsteffen]

Could we use rust-lang/rust#89570 when that is ready?

[Jarcho]

A quick look says no. Two things that are different

1. Exhaustiveness checking is comparing patterns checking if there is anything which doesn't overlap. This is checking if there is anything which does overlap.
2. Exhaustiveness checking does a rolling comparison (p1 with p2, p1+p2 with p3...). This needs a full pairwise comparison to work.

[Jarcho]

Basically done now. Just need to clarify the message for which direction the patterns need to be merged. In some cases it can only be merged in one direction. e.g.

match foo {
    Foo::A(0) => x, // can be Foo::A(0) | Foo::B(0)
    Foo::A(_) => y,
    Foo::B(0) => x, // can't merge Foo::A(0) here
}

If Foo::A(_) were changed to Foo::B(_) the merge would have to go in the opposite direction. If it were instead Foo::C then either change would work. I'm not really sure the best way to display that in the message.

[bors]

☔ The latest upstream changes (presumably #8310) made this pull request unmergeable. Please resolve the merge conflicts.

[xFrednet]

Hey @Jarcho, this PR is on my todo list but sadly a bit too big to review on the side (That's why I haven't left a review yet). I'll be free in about two weeks, would it be alright if I keep this in my backlog until then? Otherwise, I can also see if someone else wants to review this 🙃

[Jarcho]

The issue's been open for more than five years. I think it can wait a couple weeks. Now get back to your thesis.

[xFrednet]

😂 Will do, thanks! 🙃

[bors]

☔ The latest upstream changes (presumably #8322) made this pull request unmergeable. Please resolve the merge conflicts.

[xFrednet]

Alright, I've looked through the implementation and everything looks good to me. I've marked some smaller nits but nothing major. I still have to go through the tests and test output. But you can rebase if you want.

Thank you very much for giving me the time to write on my thesis. It took quite some work, But I'm happy with the result.

[xFrednet]

Okay, I've also looked through the test and the output looks really clean 👍. This should be ready for merging after a rebase and after the comments have been addressed 🙃

[xFrednet]

Hey @Jarcho, this is a ping from triage. Do you plan to continue working on this PR? The direction and changes still look good to me, besides the NITs 🙃

[Jarcho]

Still need to look into your last point. It's on the list of things to do.

[xFrednet]

Looks good to me! Thank you for the refactoring. I've also tested this implementation with lintcheck and everything looks good. 👍 💪

@bors r+

[bors]

📌 Commit 773d203 has been approved by xFrednet

[bors]

⌛ Testing commit 773d203 with merge f07ee8a...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing f07ee8a to master...