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Relax priv-in-pub lint on generic bounds and where clauses of trait impls. #90586

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merged 1 commit into from
Dec 28, 2021

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jswrenn
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@jswrenn jswrenn commented Nov 4, 2021

The priv-in-pub lint is a legacy mechanism of the compiler, supplanted by a reachability-based type privacy analysis. This PR does not relax type privacy; it only relaxes the lint (as proposed by the type privacy RFC) in the case of trait impls.

Current Behavior

On public trait impls, it's currently an error to have a where bound constraining a private type with a trait:

pub trait Trait {}
pub struct Type {}

struct Priv {}
impl Trait for Priv {}

impl Trait for Type
where
    Priv: Trait // ERROR
{}

...and it's a warning to have have a public type constrained by a private trait:

pub trait Trait {}
pub struct Type {}

pub struct Pub {}
trait Priv {}
impl Priv for Pub {}

impl Trait for Type
where
    Pub: Priv // WARNING
{}

This lint applies to where clauses in other contexts, too; e.g. on free functions:

struct Priv<T>(T);
pub trait Pub {}
impl<T: Pub> Pub for Priv<T> {}

pub fn function<T>()
where
    Priv<T>: Pub // WARNING
{}

These constraints could be relaxed without issue.

New Behavior

This lint is relaxed for where clauses on trait impls, such that it's okay to have a where bound constraining a private type with a trait:

pub trait Trait {}
pub struct Type {}

struct Priv {}
impl Trait for Priv {}

impl Trait for Type
where
    Priv: Trait // OK
{}

...and it's okay to have a public type constrained by a private trait:

pub trait Trait {}
pub struct Type {}

pub struct Pub {}
trait Priv {}
impl Priv for Pub {}

impl Trait for Type
where
    Pub: Priv // OK
{}

Rationale

While the priv-in-pub lint is not essential for soundness, it can help programmers avoid pitfalls that would make their libraries difficult to use by others. For instance, such a lint is useful for free functions; e.g. if a downstream crate tries to call the function in the previous snippet in a generic context:

fn callsite<T>()
where
    Priv<T>: Pub // ERROR: omitting this bound is a compile error, but including it is too
{
    function::<T>()
}

...it cannot do so without repeating function's where bound, which we cannot do because Priv is out-of-scope. A lint for this case is arguably helpful.

However, this same reasoning doesn't hold for trait impls. To call an unconstrained method on a public trait impl with private bounds, you don't need to forward those private bounds, you can forward the public trait:

mod upstream {
    pub trait Trait {
        fn method(&self) {}
    }
    pub struct Type<T>(T);
    
    pub struct Pub<T>(T);
    trait Priv {}
    impl<T: Priv> Priv for Pub<T> {}
    
    impl<T> Trait for Type<T>
    where
        Pub<T>: Priv // WARNING
    {}
}

mod downstream {
    use super::upstream::*;
    
    fn function<T>(value: Type<T>)
    where
        Type<T>: Trait // <- no private deets!
    {
        value.method();
    }
}

This PR only eliminates the lint on trait impls. It leaves it intact for all other contexts, including trait definitions, inherent impls, and function definitions. It doesn't need to exist in those cases either, but I figured I'd first target a case where it's mostly pointless.

Other Notes

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r? @Mark-Simulacrum

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

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Nov 4, 2021
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r? @petrochenkov

@apiraino apiraino added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Nov 11, 2021
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I'm going to send this to the lang team for sanity checking.

This PR removes the private-in-public warnings from generic bounds and where clauses on impl items specifically.

@petrochenkov petrochenkov added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). T-lang Relevant to the language team, which will review and decide on the PR/issue. I-lang-nominated Nominated for discussion during a lang team meeting. and removed T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 15, 2021
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@petrochenkov I cannot quite tell from your comment what your take is here -- do you feel this is in the spirit of the original RFC? In what way does it differ? It seems surprising to me that you would say it conforms or not to the RFC based on whether the lint in the RFC is allow by default.

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do you feel this is in the spirit of the original RFC?

It's in the spirit of the RFC.
The RFC is just not entirely precise

This lint replaces part of private-in-public errors and can be reported as warn-by-default or allow-by-default.

Back then I wanted to start with warn-by-default to get some experience, but maybe be we already have enough experience to just allow it now.

@jswrenn
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jswrenn commented Nov 17, 2021

This PR also draws a finer distinction than the proposed Lint #2 makes: this PR distinguishes between private items in the bounds of trait impls, and private items in other bounds. I describe the rationale for this distinction in the description of this PR, and this PR only impacts private items in the where bounds of trait impls.


@scottmcm suggested that all uses of private items in bounds should be allowed, but this PR doesn't go that far. I'm inclined to agree, though. The only danger of private items in bounds is that end-users can't 'forward' such bounds when they're writing generic code. But:

  • not all bounds need to be forwarded
  • you can already write un-forwardable bounds, just by adding a tad of indirection
  • sometimes unforwardable bounds are desirable

So, the lint proposed proposed by the type privacy RFC would just a heuristic that sometimes helps avoid an API design decision that sometimes is a pitfall. There's enough "sometimes"s in there, that I'd argue such a lint would probably be more at home in clippy than rustc.

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FWIW, I like the middle-ground proposed here. The OP did a good job convincing me that the "you can forward the public trait" is an interesting distinction. We can always remove more cases later.

@scottmcm
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We didn't have time to go into this in detail in today's lang team meeting, so let's try to make progress async:

@rfcbot fcp merge

The OP here has a good description of what this allows. People seem to want to do this enough that the workarounds are well-known; I think we should just allow it directly.

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rfcbot commented Nov 30, 2021

Team member @scottmcm 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 Nov 30, 2021
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@rfcbot reviewed

@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 Dec 7, 2021
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rfcbot commented Dec 7, 2021

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

@nikomatsakis nikomatsakis removed the I-lang-nominated Nominated for discussion during a lang team meeting. label Dec 14, 2021
@rfcbot rfcbot added finished-final-comment-period The final comment period is finished for this PR / Issue. to-announce Announce this issue on triage meeting and removed final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. labels Dec 17, 2021
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rfcbot commented Dec 17, 2021

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.

This will be merged soon.

@petrochenkov petrochenkov added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Dec 26, 2021
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r=me after squashing commits and removing accidental changes from the resulting commit.

@petrochenkov petrochenkov added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Dec 26, 2021
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@bors r+

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bors commented Dec 27, 2021

📌 Commit ebef8a8 has been approved by petrochenkov

@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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 27, 2021
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bors commented Dec 27, 2021

⌛ Testing commit ebef8a8 with merge 1c74c60a963806a73f5fcb12ebf3c7cf1e8b7b16...

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bors commented Dec 27, 2021

💔 Test failed - checks-actions

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

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ehuss commented Dec 27, 2021

@bors retry

network error

@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 Dec 27, 2021
bors added a commit to rust-lang-ci/rust that referenced this pull request Dec 27, 2021
…askrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#90586 (Relax priv-in-pub lint on generic bounds and where clauses of trait impls.)
 - rust-lang#92112 (Fix the error of checking `base_expr` twice in type_changing_struct_update)
 - rust-lang#92147 (rustc_builtin_macros: make asm mod public for rustfmt)
 - rust-lang#92161 (resolve: Minor miscellaneous cleanups from rust-lang#89059)
 - rust-lang#92264 (Remove `maybe_uninit_extra` feature from Vec docs)
 - rust-lang#92303 (Add test cases for issue rust-lang#26186)
 - rust-lang#92307 (Fix minor typos)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit b57a6b3 into rust-lang:master Dec 28, 2021
@rustbot rustbot added this to the 1.59.0 milestone Dec 28, 2021
wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request Mar 2, 2022
Pkgsrc changes:
 * Bump available bootstraps to 1.58.1.
 * Adjust one patch (and checksum) so that it still applies.

Upstream changes:

Version 1.59.0 (2022-02-24)
==========================

Language
--------

- [Stabilize default arguments for const generics][90207]
- [Stabilize destructuring assignment][90521]
- [Relax private in public lint on generic bounds and where clauses
  of trait impls][90586]
- [Stabilize asm! and global_asm! for x86, x86_64, ARM, Aarch64,
  and RISC-V][91728]

Compiler
--------

- [Stabilize new symbol mangling format, leaving it opt-in
  (-Csymbol-mangling-version=v0)][90128]
- [Emit LLVM optimization remarks when enabled with `-Cremark`][90833]
- [Fix sparc64 ABI for aggregates with floating point members][91003]
- [Warn when a `#[test]`-like built-in attribute macro is present
  multiple times.][91172]
- [Add support for riscv64gc-unknown-freebsd][91284]
- [Stabilize `-Z emit-future-incompat` as `--json future-incompat`][91535]
- [Soft disable incremental compilation][94124]

This release disables incremental compilation, unless the user has explicitly
opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable.
This is due to a known and relatively frequently occurring bug in incremental
compilation, which causes builds to issue internal compiler errors. This
particular bug is already fixed on nightly, but that fix has not yet rolled out
to stable and is deemed too risky for a direct stable backport.

As always, we encourage users to test with nightly and report bugs so that we
can track failures and fix issues earlier.

See [94124] for more details.

[94124]: rust-lang/rust#94124

Libraries
---------

- [Remove unnecessary bounds for some Hash{Map,Set} methods][91593]

Stabilized APIs
---------------

- [`std::thread::available_parallelism`][available_parallelism]
- [`Result::copied`][result-copied]
- [`Result::cloned`][result-cloned]
- [`arch::asm!`][asm]
- [`arch::global_asm!`][global_asm]
- [`ops::ControlFlow::is_break`][is_break]
- [`ops::ControlFlow::is_continue`][is_continue]
- [`TryFrom<char> for u8`][try_from_char_u8]
- [`char::TryFromCharError`][try_from_char_err]
  implementing `Clone`, `Debug`, `Display`, `PartialEq`, `Copy`, `Eq`, `Error`
- [`iter::zip`][zip]
- [`NonZeroU8::is_power_of_two`][is_power_of_two8]
- [`NonZeroU16::is_power_of_two`][is_power_of_two16]
- [`NonZeroU32::is_power_of_two`][is_power_of_two32]
- [`NonZeroU64::is_power_of_two`][is_power_of_two64]
- [`NonZeroU128::is_power_of_two`][is_power_of_two128]
- [`DoubleEndedIterator for ToLowercase`][lowercase]
- [`DoubleEndedIterator for ToUppercase`][uppercase]
- [`TryFrom<&mut [T]> for [T; N]`][tryfrom_ref_arr]
- [`UnwindSafe for Once`][unwindsafe_once]
- [`RefUnwindSafe for Once`][refunwindsafe_once]
- [armv8 neon intrinsics for aarch64][stdarch/1266]

Const-stable:

- [`mem::MaybeUninit::as_ptr`][muninit_ptr]
- [`mem::MaybeUninit::assume_init`][muninit_init]
- [`mem::MaybeUninit::assume_init_ref`][muninit_init_ref]
- [`ffi::CStr::from_bytes_with_nul_unchecked`][cstr_from_bytes]

Cargo
-----

- [Stabilize the `strip` profile option][cargo/10088]
- [Stabilize future-incompat-report][cargo/10165]
- [Support abbreviating `--release` as `-r`][cargo/10133]
- [Support `term.quiet` configuration][cargo/10152]
- [Remove `--host` from cargo {publish,search,login}][cargo/10145]

Compatibility Notes
-------------------

- [Refactor weak symbols in std::sys::unix][90846]
  This may add new, versioned, symbols when building with a newer glibc, as the
  standard library uses weak linkage rather than dynamically attempting to load
  certain symbols at runtime.
- [Deprecate crate_type and crate_name nested inside `#![cfg_attr]`][83744]
  This adds a future compatibility lint to supporting the use of cfg_attr
  wrapping either crate_type or crate_name specification within Rust files;
  it is recommended that users migrate to setting the equivalent command line
  flags.
- [Remove effect of `#[no_link]` attribute on name resolution][92034]
  This may expose new names, leading to conflicts with preexisting names in a
  given namespace and a compilation failure.
- [Cargo will document libraries before binaries.][cargo/10172]
- [Respect doc=false in dependencies, not just the root crate][cargo/10201]
- [Weaken guarantee around advancing underlying iterators in zip][83791]
- [Make split_inclusive() on an empty slice yield an empty output][89825]
- [Update std::env::temp_dir to use GetTempPath2 on Windows when
  available.][89999]
- [unreachable! was updated to match other formatting macro behavior
  on Rust 2021][92137]

Internal Changes
----------------

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

- [Fix many cases of normalization-related ICEs][91255]
- [Replace dominators algorithm with simple Lengauer-Tarjan][85013]
- [Store liveness in interval sets for region inference][90637]

- [Remove `in_band_lifetimes` from the compiler and standard library,
  in preparation for removing this unstable feature.][91867]

[91867]: rust-lang/rust#91867
[83744]: rust-lang/rust#83744
[83791]: rust-lang/rust#83791
[85013]: rust-lang/rust#85013
[89825]: rust-lang/rust#89825
[89999]: rust-lang/rust#89999
[90128]: rust-lang/rust#90128
[90207]: rust-lang/rust#90207
[90521]: rust-lang/rust#90521
[90586]: rust-lang/rust#90586
[90637]: rust-lang/rust#90637
[90833]: rust-lang/rust#90833
[90846]: rust-lang/rust#90846
[91003]: rust-lang/rust#91003
[91172]: rust-lang/rust#91172
[91255]: rust-lang/rust#91255
[91284]: rust-lang/rust#91284
[91535]: rust-lang/rust#91535
[91593]: rust-lang/rust#91593
[91728]: rust-lang/rust#91728
[91878]: rust-lang/rust#91878
[91896]: rust-lang/rust#91896
[91926]: rust-lang/rust#91926
[91984]: rust-lang/rust#91984
[92020]: rust-lang/rust#92020
[92034]: rust-lang/rust#92034
[92483]: rust-lang/rust#92483
[cargo/10088]: rust-lang/cargo#10088
[cargo/10133]: rust-lang/cargo#10133
[cargo/10145]: rust-lang/cargo#10145
[cargo/10152]: rust-lang/cargo#10152
[cargo/10165]: rust-lang/cargo#10165
[cargo/10172]: rust-lang/cargo#10172
[cargo/10201]: rust-lang/cargo#10201
[cargo/10269]: rust-lang/cargo#10269

[cstr_from_bytes]: https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#method.from_bytes_with_nul_unchecked
[muninit_ptr]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr
[muninit_init]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init
[muninit_init_ref]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref
[unwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-UnwindSafe
[refunwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-RefUnwindSafe
[tryfrom_ref_arr]: https://doc.rust-lang.org/stable/std/convert/trait.TryFrom.html#impl-TryFrom%3C%26%27_%20mut%20%5BT%5D%3E
[lowercase]: https://doc.rust-lang.org/stable/std/char/struct.ToLowercase.html#impl-DoubleEndedIterator
[uppercase]: https://doc.rust-lang.org/stable/std/char/struct.ToUppercase.html#impl-DoubleEndedIterator
[try_from_char_err]: https://doc.rust-lang.org/stable/std/char/struct.TryFromCharError.html
[available_parallelism]: https://doc.rust-lang.org/stable/std/thread/fn.available_parallelism.html
[result-copied]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.copied
[result-cloned]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.cloned
[asm]: https://doc.rust-lang.org/stable/core/arch/macro.asm.html
[global_asm]: https://doc.rust-lang.org/stable/core/arch/macro.global_asm.html
[is_break]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_break
[is_continue]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_continue
[try_from_char_u8]: https://doc.rust-lang.org/stable/std/primitive.char.html#impl-TryFrom%3Cchar%3E
[zip]: https://doc.rust-lang.org/stable/std/iter/fn.zip.html
[is_power_of_two8]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU8.html#method.is_power_of_two
[is_power_of_two16]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU16.html#method.is_power_of_two
[is_power_of_two32]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU32.html#method.is_power_of_two
[is_power_of_two64]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU64.html#method.is_power_of_two
[is_power_of_two128]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU128.html#method.is_power_of_two
[stdarch/1266]: rust-lang/stdarch#1266
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Apr 15, 2022
Pkgsrc changes:
 * Bump available bootstraps to 1.58.1.
 * Adjust one patch (and checksum) so that it still applies.

Upstream changes:

Version 1.59.0 (2022-02-24)
==========================

Language
--------

- [Stabilize default arguments for const generics][90207]
- [Stabilize destructuring assignment][90521]
- [Relax private in public lint on generic bounds and where clauses
  of trait impls][90586]
- [Stabilize asm! and global_asm! for x86, x86_64, ARM, Aarch64,
  and RISC-V][91728]

Compiler
--------

- [Stabilize new symbol mangling format, leaving it opt-in
  (-Csymbol-mangling-version=v0)][90128]
- [Emit LLVM optimization remarks when enabled with `-Cremark`][90833]
- [Fix sparc64 ABI for aggregates with floating point members][91003]
- [Warn when a `#[test]`-like built-in attribute macro is present
  multiple times.][91172]
- [Add support for riscv64gc-unknown-freebsd][91284]
- [Stabilize `-Z emit-future-incompat` as `--json future-incompat`][91535]
- [Soft disable incremental compilation][94124]

This release disables incremental compilation, unless the user has explicitly
opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable.
This is due to a known and relatively frequently occurring bug in incremental
compilation, which causes builds to issue internal compiler errors. This
particular bug is already fixed on nightly, but that fix has not yet rolled out
to stable and is deemed too risky for a direct stable backport.

As always, we encourage users to test with nightly and report bugs so that we
can track failures and fix issues earlier.

See [94124] for more details.

[94124]: rust-lang/rust#94124

Libraries
---------

- [Remove unnecessary bounds for some Hash{Map,Set} methods][91593]

Stabilized APIs
---------------

- [`std::thread::available_parallelism`][available_parallelism]
- [`Result::copied`][result-copied]
- [`Result::cloned`][result-cloned]
- [`arch::asm!`][asm]
- [`arch::global_asm!`][global_asm]
- [`ops::ControlFlow::is_break`][is_break]
- [`ops::ControlFlow::is_continue`][is_continue]
- [`TryFrom<char> for u8`][try_from_char_u8]
- [`char::TryFromCharError`][try_from_char_err]
  implementing `Clone`, `Debug`, `Display`, `PartialEq`, `Copy`, `Eq`, `Error`
- [`iter::zip`][zip]
- [`NonZeroU8::is_power_of_two`][is_power_of_two8]
- [`NonZeroU16::is_power_of_two`][is_power_of_two16]
- [`NonZeroU32::is_power_of_two`][is_power_of_two32]
- [`NonZeroU64::is_power_of_two`][is_power_of_two64]
- [`NonZeroU128::is_power_of_two`][is_power_of_two128]
- [`DoubleEndedIterator for ToLowercase`][lowercase]
- [`DoubleEndedIterator for ToUppercase`][uppercase]
- [`TryFrom<&mut [T]> for [T; N]`][tryfrom_ref_arr]
- [`UnwindSafe for Once`][unwindsafe_once]
- [`RefUnwindSafe for Once`][refunwindsafe_once]
- [armv8 neon intrinsics for aarch64][stdarch/1266]

Const-stable:

- [`mem::MaybeUninit::as_ptr`][muninit_ptr]
- [`mem::MaybeUninit::assume_init`][muninit_init]
- [`mem::MaybeUninit::assume_init_ref`][muninit_init_ref]
- [`ffi::CStr::from_bytes_with_nul_unchecked`][cstr_from_bytes]

Cargo
-----

- [Stabilize the `strip` profile option][cargo/10088]
- [Stabilize future-incompat-report][cargo/10165]
- [Support abbreviating `--release` as `-r`][cargo/10133]
- [Support `term.quiet` configuration][cargo/10152]
- [Remove `--host` from cargo {publish,search,login}][cargo/10145]

Compatibility Notes
-------------------

- [Refactor weak symbols in std::sys::unix][90846]
  This may add new, versioned, symbols when building with a newer glibc, as the
  standard library uses weak linkage rather than dynamically attempting to load
  certain symbols at runtime.
- [Deprecate crate_type and crate_name nested inside `#![cfg_attr]`][83744]
  This adds a future compatibility lint to supporting the use of cfg_attr
  wrapping either crate_type or crate_name specification within Rust files;
  it is recommended that users migrate to setting the equivalent command line
  flags.
- [Remove effect of `#[no_link]` attribute on name resolution][92034]
  This may expose new names, leading to conflicts with preexisting names in a
  given namespace and a compilation failure.
- [Cargo will document libraries before binaries.][cargo/10172]
- [Respect doc=false in dependencies, not just the root crate][cargo/10201]
- [Weaken guarantee around advancing underlying iterators in zip][83791]
- [Make split_inclusive() on an empty slice yield an empty output][89825]
- [Update std::env::temp_dir to use GetTempPath2 on Windows when
  available.][89999]
- [unreachable! was updated to match other formatting macro behavior
  on Rust 2021][92137]

Internal Changes
----------------

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

- [Fix many cases of normalization-related ICEs][91255]
- [Replace dominators algorithm with simple Lengauer-Tarjan][85013]
- [Store liveness in interval sets for region inference][90637]

- [Remove `in_band_lifetimes` from the compiler and standard library,
  in preparation for removing this unstable feature.][91867]

[91867]: rust-lang/rust#91867
[83744]: rust-lang/rust#83744
[83791]: rust-lang/rust#83791
[85013]: rust-lang/rust#85013
[89825]: rust-lang/rust#89825
[89999]: rust-lang/rust#89999
[90128]: rust-lang/rust#90128
[90207]: rust-lang/rust#90207
[90521]: rust-lang/rust#90521
[90586]: rust-lang/rust#90586
[90637]: rust-lang/rust#90637
[90833]: rust-lang/rust#90833
[90846]: rust-lang/rust#90846
[91003]: rust-lang/rust#91003
[91172]: rust-lang/rust#91172
[91255]: rust-lang/rust#91255
[91284]: rust-lang/rust#91284
[91535]: rust-lang/rust#91535
[91593]: rust-lang/rust#91593
[91728]: rust-lang/rust#91728
[91878]: rust-lang/rust#91878
[91896]: rust-lang/rust#91896
[91926]: rust-lang/rust#91926
[91984]: rust-lang/rust#91984
[92020]: rust-lang/rust#92020
[92034]: rust-lang/rust#92034
[92483]: rust-lang/rust#92483
[cargo/10088]: rust-lang/cargo#10088
[cargo/10133]: rust-lang/cargo#10133
[cargo/10145]: rust-lang/cargo#10145
[cargo/10152]: rust-lang/cargo#10152
[cargo/10165]: rust-lang/cargo#10165
[cargo/10172]: rust-lang/cargo#10172
[cargo/10201]: rust-lang/cargo#10201
[cargo/10269]: rust-lang/cargo#10269

[cstr_from_bytes]: https://doc.rust-lang.org/stable/std/ffi/struct.CStr.html#method.from_bytes_with_nul_unchecked
[muninit_ptr]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr
[muninit_init]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init
[muninit_init_ref]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref
[unwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-UnwindSafe
[refunwindsafe_once]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#impl-RefUnwindSafe
[tryfrom_ref_arr]: https://doc.rust-lang.org/stable/std/convert/trait.TryFrom.html#impl-TryFrom%3C%26%27_%20mut%20%5BT%5D%3E
[lowercase]: https://doc.rust-lang.org/stable/std/char/struct.ToLowercase.html#impl-DoubleEndedIterator
[uppercase]: https://doc.rust-lang.org/stable/std/char/struct.ToUppercase.html#impl-DoubleEndedIterator
[try_from_char_err]: https://doc.rust-lang.org/stable/std/char/struct.TryFromCharError.html
[available_parallelism]: https://doc.rust-lang.org/stable/std/thread/fn.available_parallelism.html
[result-copied]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.copied
[result-cloned]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.cloned
[asm]: https://doc.rust-lang.org/stable/core/arch/macro.asm.html
[global_asm]: https://doc.rust-lang.org/stable/core/arch/macro.global_asm.html
[is_break]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_break
[is_continue]: https://doc.rust-lang.org/stable/std/ops/enum.ControlFlow.html#method.is_continue
[try_from_char_u8]: https://doc.rust-lang.org/stable/std/primitive.char.html#impl-TryFrom%3Cchar%3E
[zip]: https://doc.rust-lang.org/stable/std/iter/fn.zip.html
[is_power_of_two8]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU8.html#method.is_power_of_two
[is_power_of_two16]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU16.html#method.is_power_of_two
[is_power_of_two32]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU32.html#method.is_power_of_two
[is_power_of_two64]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU64.html#method.is_power_of_two
[is_power_of_two128]: https://doc.rust-lang.org/stable/core/num/struct.NonZeroU128.html#method.is_power_of_two
[stdarch/1266]: rust-lang/stdarch#1266
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