Add [T; N]: TryFrom<Vec<T>> (insta-stable)

[scottmcm]

This is very similar to the existing Box<[T; N]>: TryFrom<Box<[T]>>, but allows avoiding the shrink_to_fit if you have a vector and not a boxed slice.

Like the slice equivalents of this, it fails if the length of the vector is not exactly N.
This uses Vec<T> as the Error type to return the input, like how the Rc<[T]> -> Rc<[T; N]> (and Arc) ones also reflect the input directly in the error type.

#[stable(feature = "array_try_from_vec", since = "1.47.0")]
impl<T, const N: usize> TryFrom<Vec<T>> for [T; N] {
    type Error = Vec<T>;
    fn try_from(mut vec: Vec<T>) -> Result<[T; N], Vec<T>>;
}

Inspired by this zulip thread: https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/APIs.20for.20getting.20stuff.20from.20a.20Vec.20by.20owned/near/209048103

[rust-highfive]

r? @LukasKalbertodt

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[LukasKalbertodt]

Code looks good (apart from Rust version nit). Having Vec<T> be the error type also makes sense to me.

As this is insta-stable and I can't start FCPs:
r? @KodrAus

[LukasKalbertodt]

Oh right, review comments are not picked up.

r? @KodrAus

[KodrAus]

Thanks @scottmcm! This looks good to me.

@rfcbot fcp merge

[rfcbot]

Team member @KodrAus has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @KodrAus
• @dtolnay
• @sfackler
• @withoutboats

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.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

The RFC will be merged soon.

[dtolnay]

@bors r+

[bors]

📌 Commit 3d89ee9 has been approved by dtolnay

[scottmcm]

It's unclear to me what happened here -- maybe the job just never started? https://buildbot2.rust-lang.org/homu/results/rust/76310

@bors retry

[bors]

⌛ Testing commit 3d89ee9 with merge f976b4641b963dbcc1ed4edb155fce5db28807b1...

[bors]

💔 Test failed - checks-actions

[dtolnay]

Can't tell what failed. This is the only failing job I see: seemed to be working then got killed with signal 9.

    Finished release [optimized] target(s) in 1m 05s
[TIMING] ToolBuild { compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-apple-darwin", file: None } }, target: TargetSelection { triple: "x86_64-apple-darwin", file: None }, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, is_optional_tool: false, source_type: InTree, extra_features: [] } -- 65.034
[TIMING] Tidy { compiler: Compiler { stage: 0, host: TargetSelection { triple: "x86_64-apple-darwin", file: None } }, target: TargetSelection { triple: "x86_64-apple-darwin", file: None } } -- 0.000
tidy check


command did not execute successfully: "/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage0-tools-bin/tidy" "/Users/runner/work/rust/rust" "/Users/runner/work/rust/rust/build/x86_64-apple-darwin/stage0/bin/cargo"
expected success, got: signal: 9


failed to run: /Users/runner/work/rust/rust/build/bootstrap/debug/bootstrap --stage 2 test
Build completed unsuccessfully in 0:01:13

@bors retry

[RalfJung]

@bors rollup