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Add [T; N]: TryFrom<Vec<T>> (insta-stable) #76310

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merged 3 commits into from
Sep 19, 2020

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@scottmcm scottmcm commented Sep 4, 2020

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

@scottmcm scottmcm added T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. needs-fcp This change is insta-stable, so needs a completed FCP to proceed. labels Sep 4, 2020
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r? @LukasKalbertodt

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@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 4, 2020
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.
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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

library/alloc/src/vec.rs Outdated Show resolved Hide resolved
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Oh right, review comments are not picked up.

r? @KodrAus

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KodrAus commented Sep 6, 2020

Thanks @scottmcm! This looks good to me.

@rfcbot fcp merge

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rfcbot commented Sep 6, 2020

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

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 rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Sep 6, 2020
library/alloc/src/vec.rs Outdated Show resolved Hide resolved
Thanks, Amanieu

Co-authored-by: Amanieu d'Antras <[email protected]>
@rfcbot rfcbot added final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. and removed proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. labels Sep 7, 2020
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rfcbot commented Sep 7, 2020

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

@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Sep 17, 2020
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rfcbot commented Sep 17, 2020

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.

@rfcbot rfcbot added the to-announce Announce this issue on triage meeting label Sep 17, 2020
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dtolnay commented Sep 17, 2020

@bors r+

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bors commented Sep 17, 2020

📌 Commit 3d89ee9 has been approved by dtolnay

@bors bors added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 17, 2020
@spastorino spastorino removed the to-announce Announce this issue on triage meeting label Sep 17, 2020
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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 bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 17, 2020
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bors commented Sep 17, 2020

⌛ Testing commit 3d89ee9 with merge f976b4641b963dbcc1ed4edb155fce5db28807b1...

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bors commented Sep 17, 2020

💔 Test failed - checks-actions

@bors bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 17, 2020
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dtolnay commented Sep 19, 2020

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

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 19, 2020
RalfJung added a commit to RalfJung/rust that referenced this pull request Sep 19, 2020
Add `[T; N]: TryFrom<Vec<T>>` (insta-stable)

This is very similar to the [existing](https://doc.rust-lang.org/nightly/std/convert/trait.TryFrom.html#impl-TryFrom%3CBox%3C%5BT%5D%3E%3E) `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.

```rust
#[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
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@bors rollup

bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 19, 2020
Rollup of 14 pull requests

Successful merges:

 - rust-lang#73963 (deny(unsafe_op_in_unsafe_fn) in libstd/path.rs)
 - rust-lang#75099 (lint/ty: move fns to avoid abstraction violation)
 - rust-lang#75502 (Use implicit (not explicit) rules for promotability by default in `const fn`)
 - rust-lang#75580 (Add test for checking duplicated branch or-patterns)
 - rust-lang#76310 (Add `[T; N]: TryFrom<Vec<T>>` (insta-stable))
 - rust-lang#76400 (Clean up vec benches bench_in_place style)
 - rust-lang#76434 (do not inline black_box when building for Miri)
 - rust-lang#76492 (Add associated constant `BITS` to all integer types)
 - rust-lang#76525 (Add as_str() to string::Drain.)
 - rust-lang#76636 (assert ScalarMaybeUninit size)
 - rust-lang#76749 (give *even better* suggestion when matching a const range)
 - rust-lang#76757 (don't convert types to the same type with try_into (clippy::useless_conversion))
 - rust-lang#76796 (Give a better error message when x.py uses the wrong stage for CI)
 - rust-lang#76798 (Build fixes for RISC-V 32-bit Linux support)

Failed merges:

r? `@ghost`
@bors bors merged commit bac2f39 into rust-lang:master Sep 19, 2020
@rustbot rustbot added this to the 1.48.0 milestone Sep 19, 2020
@scottmcm scottmcm deleted the array-try_from-vec branch September 19, 2020 19:27
wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request Nov 24, 2020
Clean up some of the pkgsrc Makefile, there's still lots in here that
should just be deleted though.  Switch SunOS to the illumos bootstrap
by default.

Version 1.48.0 (2020-11-19)
==========================

Language
--------

- [The `unsafe` keyword is now syntactically permitted on modules.][75857] This
  is still rejected *semantically*, but can now be parsed by procedural macros.

Compiler
--------
- [Stabilised the `-C link-self-contained=<yes|no>` compiler flag.][76158] This tells
  `rustc` whether to link its own C runtime and libraries or to rely on a external
  linker to find them. (Supported only on `windows-gnu`, `linux-musl`, and `wasi` platforms.)
- [You can now use `-C target-feature=+crt-static` on `linux-gnu` targets.][77386]
  Note: If you're using cargo you must explicitly pass the `--target` flag.
- [Added tier 2\* support for `aarch64-unknown-linux-musl`.][76420]

\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.

Libraries
---------
- [`io::Write` is now implemented for `&ChildStdin` `&Sink`, `&Stdout`,
  and `&Stderr`.][76275]
- [All arrays of any length now implement `TryFrom<Vec<T>>`.][76310]
- [The `matches!` macro now supports having a trailing comma.][74880]
- [`Vec<A>` now implements `PartialEq<[B]>` where `A: PartialEq<B>`.][74194]
- [The `RefCell::{replace, replace_with, clone}` methods now all use `#[track_caller]`.][77055]

Stabilized APIs
---------------
- [`slice::as_ptr_range`]
- [`slice::as_mut_ptr_range`]
- [`VecDeque::make_contiguous`]
- [`future::pending`]
- [`future::ready`]

The following previously stable methods are now `const fn`'s:

- [`Option::is_some`]
- [`Option::is_none`]
- [`Option::as_ref`]
- [`Result::is_ok`]
- [`Result::is_err`]
- [`Result::as_ref`]
- [`Ordering::reverse`]
- [`Ordering::then`]

Cargo
-----

Rustdoc
-------
- [You can now link to items in `rustdoc` using the intra-doc link
  syntax.][74430] E.g. ``/// Uses [`std::future`]`` will automatically generate
  a link to `std::future`'s documentation. See ["Linking to items by
  name"][intradoc-links] for more information.
- [You can now specify `#[doc(alias = "<alias>")]` on items to add search aliases
  when searching through `rustdoc`'s UI.][75740]

Compatibility Notes
-------------------
- [Promotion of references to `'static` lifetime inside `const fn` now follows the
  same rules as inside a `fn` body.][75502] In particular, `&foo()` will not be
  promoted to `'static` lifetime any more inside `const fn`s.
- [Associated type bindings on trait objects are now verified to meet the bounds
  declared on the trait when checking that they implement the trait.][27675]
- [When trait bounds on associated types or opaque types are ambiguous, the
  compiler no longer makes an arbitrary choice on which bound to use.][54121]
- [Fixed recursive nonterminals not being expanded in macros during
  pretty-print/reparse check.][77153] This may cause errors if your macro wasn't
  correctly handling recursive nonterminal tokens.
- [`&mut` references to non zero-sized types are no longer promoted.][75585]
- [`rustc` will now warn if you use attributes like `#[link_name]` or `#[cold]`
  in places where they have no effect.][73461]
- [Updated `_mm256_extract_epi8` and `_mm256_extract_epi16` signatures in
  `arch::{x86, x86_64}` to return `i32` to match the vendor signatures.][73166]
- [`mem::uninitialized` will now panic if any inner types inside a struct or enum
  disallow zero-initialization.][71274]
- [`#[target_feature]` will now error if used in a place where it has no effect.][78143]
- [Foreign exceptions are now caught by `catch_unwind` and will cause an abort.][70212]
  Note: This behaviour is not guaranteed and is still considered undefined behaviour,
  see the [`catch_unwind`] documentation for further information.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.
- [Building `rustc` from source now uses `ninja` by default over `make`.][74922]
  You can continue building with `make` by setting `ninja=false` in
  your `config.toml`.
- [cg_llvm: `fewer_names` in `uncached_llvm_type`][76030]
- [Made `ensure_sufficient_stack()` non-generic][76680]

[78143]: rust-lang/rust#78143
[76680]: rust-lang/rust#76680
[76030]: rust-lang/rust#76030
[70212]: rust-lang/rust#70212
[27675]: rust-lang/rust#27675
[54121]: rust-lang/rust#54121
[71274]: rust-lang/rust#71274
[77386]: rust-lang/rust#77386
[77153]: rust-lang/rust#77153
[77055]: rust-lang/rust#77055
[76275]: rust-lang/rust#76275
[76310]: rust-lang/rust#76310
[76420]: rust-lang/rust#76420
[76158]: rust-lang/rust#76158
[75857]: rust-lang/rust#75857
[75585]: rust-lang/rust#75585
[75740]: rust-lang/rust#75740
[75502]: rust-lang/rust#75502
[74880]: rust-lang/rust#74880
[74922]: rust-lang/rust#74922
[74430]: rust-lang/rust#74430
[74194]: rust-lang/rust#74194
[73461]: rust-lang/rust#73461
[73166]: rust-lang/rust#73166
[intradoc-links]: https://doc.rust-lang.org/rustdoc/linking-to-items-by-name.html
[`catch_unwind`]: https://doc.rust-lang.org/std/panic/fn.catch_unwind.html
[`Option::is_some`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_some
[`Option::is_none`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_none
[`Option::as_ref`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.as_ref
[`Result::is_ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_ok
[`Result::is_err`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_err
[`Result::as_ref`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.as_ref
[`Ordering::reverse`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.reverse
[`Ordering::then`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.then
[`slice::as_ptr_range`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_ptr_range
[`slice::as_mut_ptr_range`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_mut_ptr_range
[`VecDeque::make_contiguous`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.make_contiguous
[`future::pending`]: https://doc.rust-lang.org/std/future/fn.pending.html
[`future::ready`]: https://doc.rust-lang.org/std/future/fn.ready.html
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jan 1, 2021
Pkgsrc changes:
 * Compensate for files being moved around upstream.
 * Introduce optional, on-by-default semi-static building of cargo,
   using the internal curl and openssl sources.  This reduces the dynamic
   dependencies of cargo and therefore the rust package itself.
   Ref. options.mk.
 * The 1.47.0 bootstrap kits have been re-built with the above option
   turned on, so no longer depends on curl or openssl from pkgsrc and/or
   from earlier OS or pkgsrc versions.  This should hopefully fix
   installation of rust with non-default PREFIX, ref. PR#54453.


Upstream changes:

Version 1.48.0 (2020-11-19)
==========================

Language
--------
- [The `unsafe` keyword is now syntactically permitted on modules.][75857] This
  is still rejected *semantically*, but can now be parsed by procedural macros.

Compiler
--------
- [Stabilised the `-C link-self-contained=<yes|no>` compiler flag.][76158]
  This tells `rustc` whether to link its own C runtime and libraries
  or to rely on a external linker to find them. (Supported only on
  `windows-gnu`, `linux-musl`, and `wasi` platforms.)
- [You can now use `-C target-feature=+crt-static` on `linux-gnu` targets.]
  [77386]
  Note: If you're using cargo you must explicitly pass the `--target` flag.
- [Added tier 2\* support for `aarch64-unknown-linux-musl`.][76420]

\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.

Libraries
---------
- [`io::Write` is now implemented for `&ChildStdin` `&Sink`, `&Stdout`,
  and `&Stderr`.][76275]
- [All arrays of any length now implement `TryFrom<Vec<T>>`.][76310]
- [The `matches!` macro now supports having a trailing comma.][74880]
- [`Vec<A>` now implements `PartialEq<[B]>` where `A: PartialEq<B>`.][74194]
- [The `RefCell::{replace, replace_with, clone}` methods now all use
  `#[track_caller]`.][77055]

Stabilized APIs
---------------
- [`slice::as_ptr_range`]
- [`slice::as_mut_ptr_range`]
- [`VecDeque::make_contiguous`]
- [`future::pending`]
- [`future::ready`]

The following previously stable methods are now `const fn`'s:

- [`Option::is_some`]
- [`Option::is_none`]
- [`Option::as_ref`]
- [`Result::is_ok`]
- [`Result::is_err`]
- [`Result::as_ref`]
- [`Ordering::reverse`]
- [`Ordering::then`]

Cargo
-----

Rustdoc
-------
- [You can now link to items in `rustdoc` using the intra-doc link
  syntax.][74430] E.g. ``/// Uses [`std::future`]`` will automatically generate
  a link to `std::future`'s documentation. See ["Linking to items by
  name"][intradoc-links] for more information.
- [You can now specify `#[doc(alias = "<alias>")]` on items to add
  search aliases when searching through `rustdoc`'s UI.][75740]

Compatibility Notes
-------------------
- [Promotion of references to `'static` lifetime inside `const fn`
  now follows the same rules as inside a `fn` body.][75502] In
  particular, `&foo()` will not be promoted to `'static` lifetime
  any more inside `const fn`s.
- [Associated type bindings on trait objects are now verified to meet the bounds
  declared on the trait when checking that they implement the trait.][27675]
- [When trait bounds on associated types or opaque types are ambiguous, the
  compiler no longer makes an arbitrary choice on which bound to use.][54121]
- [Fixed recursive nonterminals not being expanded in macros during
  pretty-print/reparse check.][77153] This may cause errors if your macro wasn't
  correctly handling recursive nonterminal tokens.
- [`&mut` references to non zero-sized types are no longer promoted.][75585]
- [`rustc` will now warn if you use attributes like `#[link_name]` or `#[cold]`
  in places where they have no effect.][73461]
- [Updated `_mm256_extract_epi8` and `_mm256_extract_epi16` signatures in
  `arch::{x86, x86_64}` to return `i32` to match the vendor signatures.][73166]
- [`mem::uninitialized` will now panic if any inner types inside
  a struct or enum disallow zero-initialization.][71274]
- [`#[target_feature]` will now error if used in a place where it
  has no effect.][78143]
- [Foreign exceptions are now caught by `catch_unwind` and will
  cause an abort.][70212] Note: This behaviour is not guaranteed
  and is still considered undefined behaviour, see the [`catch_unwind`]
  documentation for further information.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [Building `rustc` from source now uses `ninja` by default over `make`.][74922]
  You can continue building with `make` by setting `ninja=false` in
  your `config.toml`.
- [cg_llvm: `fewer_names` in `uncached_llvm_type`][76030]
- [Made `ensure_sufficient_stack()` non-generic][76680]

[78143]: rust-lang/rust#78143
[76680]: rust-lang/rust#76680
[76030]: rust-lang/rust#76030
[70212]: rust-lang/rust#70212
[27675]: rust-lang/rust#27675
[54121]: rust-lang/rust#54121
[71274]: rust-lang/rust#71274
[77386]: rust-lang/rust#77386
[77153]: rust-lang/rust#77153
[77055]: rust-lang/rust#77055
[76275]: rust-lang/rust#76275
[76310]: rust-lang/rust#76310
[76420]: rust-lang/rust#76420
[76158]: rust-lang/rust#76158
[75857]: rust-lang/rust#75857
[75585]: rust-lang/rust#75585
[75740]: rust-lang/rust#75740
[75502]: rust-lang/rust#75502
[74880]: rust-lang/rust#74880
[74922]: rust-lang/rust#74922
[74430]: rust-lang/rust#74430
[74194]: rust-lang/rust#74194
[73461]: rust-lang/rust#73461
[73166]: rust-lang/rust#73166
[intradoc-links]: https://doc.rust-lang.org/rustdoc/linking-to-items-by-name.html
[`catch_unwind`]: https://doc.rust-lang.org/std/panic/fn.catch_unwind.html
[`Option::is_some`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_some
[`Option::is_none`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_none
[`Option::as_ref`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.as_ref
[`Result::is_ok`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_ok
[`Result::is_err`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_err
[`Result::as_ref`]: https://doc.rust-lang.org/std/result/enum.Result.html#method.as_ref
[`Ordering::reverse`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.reverse
[`Ordering::then`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.then
[`slice::as_ptr_range`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_ptr_range
[`slice::as_mut_ptr_range`]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_mut_ptr_range
[`VecDeque::make_contiguous`]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.make_contiguous
[`future::pending`]: https://doc.rust-lang.org/std/future/fn.pending.html
[`future::ready`]: https://doc.rust-lang.org/std/future/fn.ready.html
bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 17, 2022
Add `Box<[T; N]>: TryFrom<Vec<T>>`

We have `[T; N]: TryFrom<Vec<T>>` (rust-lang#76310) and `Box<[T; N]>: TryFrom<Box<[T]>>`, but not this combination.

`vec.into_boxed_slice().try_into()` isn't quite a replacement for this, as that'll reallocate unnecessarily in the error case.

**Insta-stable, so needs an FCP**

(I tried to make this work with `, A`, but that's disallowed because of `#[fundamental]` rust-lang#29635 (comment))
@dtolnay dtolnay self-assigned this Mar 24, 2024
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