feat: add symmetric PartialEq impls for Vec, &[T], &mut [T] versus Cow<'_, [T]>

[kx0101]

add the missing reverse PartialEq<Cow<'_, [U]>> impls for Vec<T, A>, &[T], and &mut [T], essentially mirroring the existing forwards in library/alloc/src/vec/partial_eq.rs

partially addresses #152830. The VecDeque half of that issue is being handled separately by #152972, so there is no overlap with this PR

also fyi: verified locally with ./x test library/alloctests --stage 1 and the new test_partial_eq_cow_symmetric test passes alongside the existing alloc test suite

[rustbot]

r? @Mark-Simulacrum

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[kx0101]

had to update the two UI tests expected compiler-error snapshots so they reflect the new PartialEq<Cow<[U]>>

pretty interesting!

[Amanieu]

Starting a crater run to check if this breaks type inference in the ecosystem.

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: d8be255 (d8be25549d5418405531341b4be6d8538fc3c42e, parent: 89a99936d9e76a50e8df622e7242190841fd871b)

[Amanieu]

@craterbot check

[craterbot]

👌 Experiment pr-156160 created and queued.
🤖 Automatically detected try build d8be255
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🚧 Experiment pr-156160 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-156160 is completed!
📊 3 regressed and 0 fixed (993683 total)
📊 5174 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156160/retry-regressed-list.txt ↩

[Mark-Simulacrum]

@craterbot check crates=https://crater-reports.s3.amazonaws.com/pr-156160/retry-regressed-list.txt name=pr-156160-1 p=1

Re-running to double check the spurious regressions. 3 regressed so far aren't real.

[craterbot]

👌 Experiment pr-156160-1 created and queued.
🤖 Automatically detected try build d8be255
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[kx0101]

@Mark-Simulacrum great, thank you very much for your help! 🙏

[craterbot]

🚧 Experiment pr-156160-1 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

[craterbot]

🎉 Experiment pr-156160-1 is completed!
📊 0 regressed and 0 fixed (5021 total)
📊 551 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

Footnotes

1. re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156160-1/retry-regressed-list.txt ↩

[Mark-Simulacrum]

@rfcbot fcp merge libs-api

This adds these impls (I think these are transcribed right out of the macro). Crater didn't find any inference breakage as a result of adding them.

impl<T, U: Clone + PartialEq<T>, A: Allocator> PartialEq<Cow<'_, [U]>> for Vec<T, A> {}
impl<T, U: Clone + PartialEq<T>> PartialEq<Cow<'_, [U]>> for &[T] {}
impl<T, U: Clone + PartialEq<T>> PartialEq<Cow<'_, [U]>> for &mut [T] {}

[rust-rfcbot]

@Mark-Simulacrum has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @the8472

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[kx0101]

@Amanieu @joshtriplett @the8472 hello there! do you think we could merge this? 😄 thanks in advance!