Add check that live_region is live in sanitize_promoted

[Noble-Mushtak]

This pull request fixes #88434 by adding a check in sanitize_promoted to ensure that only regions which are actually live are added to the liveness_constraints of the BorrowCheckContext.

To implement this change, I needed to add a method to LivenessValues which gets the elements contained by a region:

/// Returns an iterator of all the elements contained by the region `r`
crate fn get_elements(&self, row: N) -> impl Iterator<Item = Location> + '_

Then, inside sanitize_promoted, we check whether the iterator returned by this method is non-empty to ensure that the region is actually live at at least one location before adding that region to the liveness_constraints of the BorrowCheckContext.

This is my first pull request to the Rust repo, so any feedback on how I can improve this pull request or if there is a better way to fix this issue would be very appreciated.

[rust-highfive]

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

Please see the contribution instructions for more information.

[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[Noble-Mushtak]

Apologies, I think I accidentally modified some submodules in my commit somehow, but I reverted and then reapplied my actual changes, so hopefully this should be fixed now.

[camelid]

Apologies, I think I accidentally modified some submodules in my commit somehow, but I reverted and then reapplied my actual changes, so hopefully this should be fixed now.

Yeah, it's easy to do that. Running git submodule update may make it so that you can't git add them by mistake (though sometimes that doesn't fix all of them). I usually run something like git add compiler/ to avoid committing submodules by mistake.

[camelid]

Might be good to add these feature flags to the test to get any "real" errors.

[camelid]

@Noble-Mushtak If you change

This pull request fixes issue #88434

to

This pull request fixes #88434

then GitHub will automatically close the issue when this PR is merged.

[wesleywiser]

r? @jackh726 or feel free to re-assign to someone more familiar with borrowck🙂

[jackh726]

r? @nikomatsakis

[nikomatsakis]

Gave this a first read. I'd like @oli-obk to take a look.

[oli-obk]

@bors r=nikomatsakis,oli-obk

I want to dig into some (preexisting) things I saw while reviewing, but nothing that should block this change

[bors]

📌 Commit 8fc329f has been approved by nikomatsakis,oli-obk

[bors]

⌛ Testing commit 8fc329f with merge 2044f12e4c5620666baf28d15401c194cedd02a0...

[bors]

💥 Test timed out

[oli-obk]

@bors retry

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

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[bors]

⌛ Testing commit 8fc329f with merge 0a56eb1...

[bors]

☀️ Test successful - checks-actions
Approved by: nikomatsakis,oli-obk
Pushing 0a56eb1 to master...

[rust-timer]

Finished benchmarking commit (0a56eb1): comparison url.

Summary: This benchmark run did not return any relevant changes.

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression