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Elaborate supertrait bounds when triggering unused_must_use on impl Trait #102287

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@compiler-errors compiler-errors commented Sep 25, 2022

Given impl Trait, if one of its supertraits has a #[must_use], then trigger the lint. This means that, for example, -> impl ExactSizeIterator also triggers the must_use on trait Iterator, which fixes #102183.

This might need @rust-lang/lang sign-off, since it changes the behavior of the lint, so cc'ing them.

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Sep 25, 2022
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r? @fee1-dead

(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 Sep 25, 2022
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@rustbot label T-lang

@rustbot rustbot added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Sep 26, 2022
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Marking as waiting on team until we get someone from lang to comment. I have no issues with the implementation.

@fee1-dead fee1-dead added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 30, 2022
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Nominating for lang team discussion.

@compiler-errors compiler-errors added the I-lang-nominated Nominated for discussion during a lang team meeting. label Oct 4, 2022
@joshtriplett joshtriplett removed the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Oct 4, 2022
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@rfcbot merge

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rfcbot commented Oct 4, 2022

Team member @joshtriplett 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 Oct 4, 2022
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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 Oct 4, 2022
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rfcbot commented Oct 4, 2022

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

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Do we do this for dyn trait, @compiler-errors ?

@joshtriplett joshtriplett added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Oct 4, 2022
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scottmcm commented Oct 4, 2022

Do we do this for dyn Trait? I think that if we do this for impl Trait, we should do it for dyn Trait too.

EDIT: Oops, raced with niko 😅

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I don't know, but I'll check!

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@nikomatsakis and @scottmcm: We don't do this for dyn Trait, but also this is complicated by the fact that we don't have let x: dyn Iterator = ..., and #[must_use] doesn't leak through references, so it would never trigger on let x: &dyn Iterator = ... anyways.

@compiler-errors compiler-errors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). labels Oct 4, 2022
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scottmcm commented Oct 4, 2022

@compiler-errors Thanks for looking into it! Sounds like it's not this PR, and I agree about references, but I do think it would be a good matching change to make Box<dyn ExactSizedIterator> trigger must_use.

@compiler-errors compiler-errors removed the I-lang-nominated Nominated for discussion during a lang team meeting. label Oct 5, 2022
@rfcbot rfcbot removed the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Oct 14, 2022
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rfcbot commented Oct 14, 2022

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.

@rfcbot rfcbot added the to-announce Announce this issue on triage meeting label Oct 14, 2022
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@bors r+

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bors commented Oct 20, 2022

📌 Commit 00a7bfc has been approved by fee1-dead

It is now in the queue for this repository.

@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 Oct 20, 2022
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Oct 20, 2022
…so-supertrait, r=fee1-dead

Elaborate supertrait bounds when triggering `unused_must_use` on `impl Trait`

Given `impl Trait`, if one of its supertraits has a `#[must_use]`, then trigger the lint. This means that, for example, `-> impl ExactSizeIterator` also triggers the `must_use` on `trait Iterator`, which fixes rust-lang#102183.

This might need `@rust-lang/lang` sign-off, since it changes the behavior of the lint, so cc'ing them.
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@bors bors 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-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 20, 2022
@rustbot rustbot added the A-testsuite Area: The testsuite used to check the correctness of rustc label Oct 20, 2022
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just had to bless a test b/c of waffle's "move lint note" pr

@bors r=fee1-dead

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bors commented Oct 20, 2022

📌 Commit 8509819 has been approved by fee1-dead

It is now in the queue for this repository.

@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 Oct 20, 2022
bors added a commit to rust-lang-ci/rust that referenced this pull request Oct 21, 2022
Rollup of 6 pull requests

Successful merges:

 - rust-lang#102287 (Elaborate supertrait bounds when triggering `unused_must_use` on `impl Trait`)
 - rust-lang#102922 (Filtering spans when emitting json)
 - rust-lang#103051 (translation: doc comments with derives, subdiagnostic-less enum variants, more derive use)
 - rust-lang#103111 (Account for hygiene in typo suggestions, and use them to point to shadowed names)
 - rust-lang#103260 (Fixup a few tests needing asm support)
 - rust-lang#103321 (rustdoc: improve appearance of source page navigation bar)

Failed merges:

 - rust-lang#103209 (Diagnostic derives: allow specifying multiple alternative suggestions)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 66d91d8 into rust-lang:master Oct 21, 2022
@rustbot rustbot added this to the 1.66.0 milestone Oct 21, 2022
@apiraino apiraino removed the to-announce Announce this issue on triage meeting label Oct 28, 2022
@compiler-errors compiler-errors deleted the unused-must-use-also-supertrait branch November 2, 2022 02:56
flip1995 pushed a commit to flip1995/rust that referenced this pull request Nov 21, 2022
Rollup of 6 pull requests

Successful merges:

 - rust-lang#102287 (Elaborate supertrait bounds when triggering `unused_must_use` on `impl Trait`)
 - rust-lang#102922 (Filtering spans when emitting json)
 - rust-lang#103051 (translation: doc comments with derives, subdiagnostic-less enum variants, more derive use)
 - rust-lang#103111 (Account for hygiene in typo suggestions, and use them to point to shadowed names)
 - rust-lang#103260 (Fixup a few tests needing asm support)
 - rust-lang#103321 (rustdoc: improve appearance of source page navigation bar)

Failed merges:

 - rust-lang#103209 (Diagnostic derives: allow specifying multiple alternative suggestions)

r? `@ghost`
`@rustbot` modify labels: rollup
wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request Dec 21, 2022
Perform a bunch of pkglint cleanup while here, and bump bootstrap kits
to 1.65.0.

Version 1.66.0 (2022-12-15)
==========================

Language
--------
- [Permit specifying explicit discriminants on all `repr(Int)`
  enums](rust-lang/rust#95710)
  ```rust
  #[repr(u8)]
  enum Foo {
      A(u8) = 0,
      B(i8) = 1,
      C(bool) = 42,
  }
  ```
- [Allow transmutes between the same type differing only in
  lifetimes](rust-lang/rust#101520)
- [Change constant evaluation errors from a deny-by-default lint to a
  hard error](rust-lang/rust#102091)
- [Trigger `must_use` on `impl Trait` for
  supertraits](rust-lang/rust#102287) This
  makes `impl ExactSizeIterator` respect the existing `#[must_use]`
  annotation on `Iterator`.
- [Allow `..X` and `..=X` in
  patterns](rust-lang/rust#102275)
- [Uplift `clippy::for_loops_over_fallibles` lint into
  rustc](rust-lang/rust#99696)
- [Stabilize `sym` operands in inline
  assembly](rust-lang/rust#103168)
- [Update to Unicode 15](rust-lang/rust#101912)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474) This is a
  soundness fix which may break code that was erroneously relying on this
  behavior.

Compiler
--------
- [Add armv5te-none-eabi and thumbv5te-none-eabi tier 3
  targets](rust-lang/rust#101329)
  - Refer to Rust's [platform support page][platform-support-doc] for
    more information on Rust's tiered platform support.
- [Add support for linking against macOS universal
  libraries](rust-lang/rust#98736)

Libraries
---------
- [Fix `#[derive(Default)]` on a generic `#[default]` enum adding
  unnecessary `Default`
  bounds](rust-lang/rust#101040)
- [Update to Unicode 15](rust-lang/rust#101821)

Stabilized APIs
---------------
- [`proc_macro::Span::source_text`](https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.source_text)
- [`uX::{checked_add_signed, overflowing_add_signed,
  saturating_add_signed,
  wrapping_add_signed}`](https://doc.rust-lang.org/stable/std/primitive.u8.html#method.checked_add_signed)
- [`iX::{checked_add_unsigned, overflowing_add_unsigned,
  saturating_add_unsigned,
  wrapping_add_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_add_unsigned)
- [`iX::{checked_sub_unsigned, overflowing_sub_unsigned,
  saturating_sub_unsigned,
  wrapping_sub_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_sub_unsigned)
- [`BTreeSet::{first, last, pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeSet.html#method.first)
- [`BTreeMap::{first_key_value, last_key_value, first_entry, last_entry,
  pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.first_key_value)
- [Add `AsFd` implementations for stdio lock types on
  WASI.](rust-lang/rust#101768)
- [`impl TryFrom<Vec<T>> for Box<[T;
  N]>`](https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#impl-TryFrom%3CVec%3CT%2C%20Global%3E%3E-for-Box%3C%5BT%3B%20N%5D%2C%20Global%3E)
- [`core::hint::black_box`](https://doc.rust-lang.org/stable/std/hint/fn.black_box.html)
- [`Duration::try_from_secs_{f32,f64}`](https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.try_from_secs_f32)
- [`Option::unzip`](https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unzip)
- [`std::os::fd`](https://doc.rust-lang.org/stable/std/os/fd/index.html)

Rustdoc
-------
- [Add Rustdoc warning for invalid HTML tags in the
  documentation](rust-lang/rust#101720)

Cargo
-----
- [Added `cargo remove` to remove dependencies from
  Cargo.toml](https://doc.rust-lang.org/nightly/cargo/commands/cargo-remove.html)
- [`cargo publish` now waits for the new version to be downloadable
  before exiting](rust-lang/cargo#11062)

See [detailed release notes](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-166-2022-12-15) for more.

Compatibility Notes
-------------------
- [Only apply `ProceduralMasquerade` hack to older versions of
  `rental`](rust-lang/rust#94063)
- [Don't export `__heap_base` and `__data_end` on
  wasm32-wasi.](rust-lang/rust#102385)
- [Don't export `__wasm_init_memory` on
  WebAssembly.](rust-lang/rust#102426)
- [Only export `__tls_*` on
  wasm32-unknown-unknown.](rust-lang/rust#102440)
- [Don't link to `libresolv` in libstd on
  Darwin](rust-lang/rust#102766)
- [Update libstd's libc to 0.2.135 (to make `libstd` no longer pull in
  `libiconv.dylib` on
  Darwin)](rust-lang/rust#103277)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474)
  This is a soundness fix which may break code that was erroneously
  relying on this behavior.
- [Make `order_dependent_trait_objects` show up in future-breakage
  reports](rust-lang/rust#102635)
- [Change std::process::Command spawning to default to inheriting the
  parent's signal mask](rust-lang/rust#101077)

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

These changes do not affect any public interfaces of Rust, but they
represent significant improvements to the performance or internals of
rustc and related tools.

- [Enable BOLT for LLVM
  compilation](rust-lang/rust#94381)
- [Enable LTO for
  rustc_driver.so](rust-lang/rust#101403)
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jan 23, 2023
Pkgsrc changes:
 * pkglint cleanups, bump bootstrap kits to 1.65.0.
 * New target: mipsel-unknown-netbsd, for cpu=mips32 with soft-float.
 * Managed to retain the build of aarch64_be, llvm needed a patch to
   avoid use of neon instructions in the BE case (llvm doesn't support
   use of neon in BE mode).  Ref. patch to
   src/llvm-project/llvm/lib/Support/BLAKE3/blake3_impl.h.
   Also submitted upstream of LLVM to the BLAKE3 maintainers.
 * The minimum gcc version is now 7.x, and that includes the
   cross-compiler for the targets.  For i386 this also needs to
   /usr/include/gcc-7 include files in the target root, because
   immintrin.h from gcc 5 is not compatible with gcc 7.x.  This
   applies for the targets where we build against a root from netbsd-8
   (sparc64, powerpc, i386), and files/gcc-wrap gets a hack for this.
 * Pick up tweak for -latomic inclusion from
   rust-lang/rust#104220
   and
   rust-lang/rust#104572
 * Retain ability to do 32-bit NetBSD, by changing from 64 to 32 bit
   types in library/std/src/sys/unix/thread_parker/netbsd.rs.
 * I've tried to get the "openssl-src" build with -latomic where it's
   needed.  I've introduced the "NetBSD-generic32" system type and use
   it for the NetBSD mipsel target.  There is another attempt to do
   the same in the patch to vendor/openssl-sys/build/main.rs.


Upstream changes:

Version 1.66.1 (2023-01-10)
===========================

- Added validation of SSH host keys for git URLs in Cargo
  ([CVE-2022-46176](https://www.cve.org/CVERecord?id=CVE-2022-46176))


Version 1.66.0 (2022-12-15)
===========================

Language
--------
- [Permit specifying explicit discriminants on all `repr(Int)`
  enums](rust-lang/rust#95710)
  ```rust
  #[repr(u8)]
  enum Foo {
      A(u8) = 0,
      B(i8) = 1,
      C(bool) = 42,
  }
  ```
- [Allow transmutes between the same type differing only in
  lifetimes](rust-lang/rust#101520)
- [Change constant evaluation errors from a deny-by-default lint to a
  hard error](rust-lang/rust#102091)
- [Trigger `must_use` on `impl Trait` for
  supertraits](rust-lang/rust#102287) This
  makes `impl ExactSizeIterator` respect the existing `#[must_use]`
  annotation on `Iterator`.
- [Allow `..X` and `..=X` in
  patterns](rust-lang/rust#102275)
- [Uplift `clippy::for_loops_over_fallibles` lint into
  rustc](rust-lang/rust#99696)
- [Stabilize `sym` operands in inline
  assembly](rust-lang/rust#103168)
- [Update to Unicode 15](rust-lang/rust#101912)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474) This is a
  soundness fix which may break code that was erroneously relying on this
  behavior.

Compiler
--------
- [Add armv5te-none-eabi and thumbv5te-none-eabi tier 3
  targets](rust-lang/rust#101329)
  - Refer to Rust's [platform support page][platform-support-doc] for
    more information on Rust's tiered platform support.
- [Add support for linking against macOS universal
  libraries](rust-lang/rust#98736)

Libraries
---------
- [Fix `#[derive(Default)]` on a generic `#[default]` enum adding
  unnecessary `Default`
  bounds](rust-lang/rust#101040)
- [Update to Unicode 15](rust-lang/rust#101821)

Stabilized APIs
---------------
- [`proc_macro::Span::source_text`](https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.source_text)
- [`uX::{checked_add_signed, overflowing_add_signed,
  saturating_add_signed,
  wrapping_add_signed}`](https://doc.rust-lang.org/stable/std/primitive.u8.html#method.checked_add_signed)
- [`iX::{checked_add_unsigned, overflowing_add_unsigned,
  saturating_add_unsigned,
  wrapping_add_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_add_unsigned)
- [`iX::{checked_sub_unsigned, overflowing_sub_unsigned,
  saturating_sub_unsigned,
  wrapping_sub_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_sub_unsigned)
- [`BTreeSet::{first, last, pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeSet.html#method.first)
- [`BTreeMap::{first_key_value, last_key_value, first_entry, last_entry,
  pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.first_key_value)
- [Add `AsFd` implementations for stdio lock types on
  WASI.](rust-lang/rust#101768)
- [`impl TryFrom<Vec<T>> for Box<[T;
  N]>`](https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#impl-TryFrom%3CVec%3CT%2C%20Global%3E%3E-for-Box%3C%5BT%3B%20N%5D%2C%20Global%3E)
- [`core::hint::black_box`](https://doc.rust-lang.org/stable/std/hint/fn.black_box.html)
- [`Duration::try_from_secs_{f32,f64}`](https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.try_from_secs_f32)
- [`Option::unzip`](https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unzip)
- [`std::os::fd`](https://doc.rust-lang.org/stable/std/os/fd/index.html)

Rustdoc
-------
- [Add Rustdoc warning for invalid HTML tags in the
  documentation](rust-lang/rust#101720)

Cargo
-----
- [Added `cargo remove` to remove dependencies from
  Cargo.toml](https://doc.rust-lang.org/nightly/cargo/commands/cargo-remove.html)
- [`cargo publish` now waits for the new version to be downloadable
  before exiting](rust-lang/cargo#11062)

See [detailed release notes](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-166-2022-12-15) for more.

Compatibility Notes
-------------------
- [Only apply `ProceduralMasquerade` hack to older versions of
  `rental`](rust-lang/rust#94063)
- [Don't export `__heap_base` and `__data_end` on
  wasm32-wasi.](rust-lang/rust#102385)
- [Don't export `__wasm_init_memory` on
  WebAssembly.](rust-lang/rust#102426)
- [Only export `__tls_*` on
  wasm32-unknown-unknown.](rust-lang/rust#102440)
- [Don't link to `libresolv` in libstd on
  Darwin](rust-lang/rust#102766)
- [Update libstd's libc to 0.2.135 (to make `libstd` no longer pull in
  `libiconv.dylib` on
  Darwin)](rust-lang/rust#103277)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474)
  This is a soundness fix which may break code that was erroneously
  relying on this behavior.
- [Make `order_dependent_trait_objects` show up in future-breakage
  reports](rust-lang/rust#102635)
- [Change std::process::Command spawning to default to inheriting the
  parent's signal mask](rust-lang/rust#101077)

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

These changes do not affect any public interfaces of Rust, but they
represent significant improvements to the performance or internals of
rustc and related tools.

- [Enable BOLT for LLVM
  compilation](rust-lang/rust#94381)
- [Enable LTO for
  rustc_driver.so](rust-lang/rust#101403)


Version 1.65.0 (2022-11-03)
==========================

Language
--------
- [Error on `as` casts of enums with `#[non_exhaustive]` variants]
  (rust-lang/rust#92744)
- [Stabilize `let else`](rust-lang/rust#93628)
- [Stabilize generic associated types (GATs)]
  (rust-lang/rust#96709)
- [Add lints `let_underscore_drop`, `let_underscore_lock`, and
  `let_underscore_must_use` from Clippy]
  (rust-lang/rust#97739)
- [Stabilize `break`ing from arbitrary labeled blocks ("label-break-value")]
  (rust-lang/rust#99332)
- [Uninitialized integers, floats, and raw pointers are now considered
  immediate UB](rust-lang/rust#98919).
  Usage of `MaybeUninit` is the correct way to work with uninitialized
  memory.
- [Stabilize raw-dylib for Windows x86_64, aarch64, and thumbv7a]
  (rust-lang/rust#99916)
- [Do not allow `Drop` impl on foreign ADTs]
  (rust-lang/rust#99576)

Compiler
--------
- [Stabilize -Csplit-debuginfo on Linux]
  (rust-lang/rust#98051)
- [Use niche-filling optimization even when multiple variants have
  data] (rust-lang/rust#94075)
- [Associated type projections are now verified to be well-formed
  prior to resolving the underlying type]
  (rust-lang/rust#99217)
- [Stringify non-shorthand visibility correctly]
  (rust-lang/rust#100350)
- [Normalize struct field types when unsizing]
  (rust-lang/rust#101831)
- [Update to LLVM 15](rust-lang/rust#99464)
- [Fix aarch64 call abi to correctly zeroext when needed]
  (rust-lang/rust#97800)
- [debuginfo: Generalize C++-like encoding for enums]
  (rust-lang/rust#98393)
- [Add `special_module_name` lint]
  (rust-lang/rust#94467)
- [Add support for generating unique profraw files by default when
  using `-C instrument-coverage`]
  (rust-lang/rust#100384)
- [Allow dynamic linking for iOS/tvOS targets]
  (rust-lang/rust#100636)

New targets:
- [Add armv4t-none-eabi as a tier 3 target]
  (rust-lang/rust#100244)
- [Add powerpc64-unknown-openbsd and riscv64-unknown-openbsd as tier 3 targets]
  (rust-lang/rust#101025)
- Refer to Rust's [platform support page][platform-support-doc] for more
  information on Rust's tiered platform support.

Libraries
---------
- [Don't generate `PartialEq::ne` in derive(PartialEq)]
  (rust-lang/rust#98655)
- [Windows RNG: Use `BCRYPT_RNG_ALG_HANDLE` by default]
  (rust-lang/rust#101325)
- [Forbid mixing `System` with direct system allocator calls]
  (rust-lang/rust#101394)
- [Document no support for writing to non-blocking stdio/stderr]
  (rust-lang/rust#101416)
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`](rust-lang/rust#95295)
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.

Stabilized APIs
---------------
- [`std::backtrace::Backtrace`]
  (https://doc.rust-lang.org/stable/std/backtrace/struct.Backtrace.html)
- [`Bound::as_ref`]
  (https://doc.rust-lang.org/stable/std/ops/enum.Bound.html#method.as_ref)
- [`std::io::read_to_string`]
  (https://doc.rust-lang.org/stable/std/io/fn.read_to_string.html)
- [`<*const T>::cast_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_mut)
- [`<*mut T>::cast_const`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_const)

These APIs are now stable in const contexts:
- [`<*const T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)
- [`<*mut T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)

Cargo
-----
- [Apply GitHub fast path even for partial hashes]
  (rust-lang/cargo#10807)
- [Do not add home bin path to PATH if it's already there]
  (rust-lang/cargo#11023)
- [Take priority into account within the pending queue]
  (rust-lang/cargo#11032).
  This slightly optimizes job scheduling by Cargo, with typically
  small improvements on larger crate graph builds.

Compatibility Notes
-------------------
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`] (rust-lang/rust#95295).
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.
- [`PollFn` now only implements `Unpin` if the closure is `Unpin`]
  (rust-lang/rust#102737).
  This is a possible breaking change if users were relying on the
  blanket unpin implementation.  See discussion on the PR for
  details of why this change was made.
- [Drop ExactSizeIterator impl from std::char::EscapeAscii]
  (rust-lang/rust#99880)
  This is a backwards-incompatible change to the standard library's
  surface area, but is unlikely to affect real world usage.
- [Do not consider a single repeated lifetime eligible for elision
  in the return type] (rust-lang/rust#103450)
  This behavior was unintentionally changed in 1.64.0, and this
  release reverts that change by making this an error again.
- [Reenable disabled early syntax gates as future-incompatibility
  lints] (rust-lang/rust#99935)
- [Update the minimum external LLVM to 13]
  (rust-lang/rust#100460)
- [Don't duplicate file descriptors into stdio fds]
  (rust-lang/rust#101426)
- [Sunset RLS](rust-lang/rust#100863)
- [Deny usage of `#![cfg_attr(..., crate_type = ...)]` to set the
  crate type] (rust-lang/rust#99784)
  This strengthens the forward compatibility lint
  deprecated_cfg_attr_crate_type_name to deny.
- [`llvm-has-rust-patches` allows setting the build system to treat
  the LLVM as having Rust-specific patches]
  (rust-lang/rust#101072)
  This option may need to be set for distributions that are building
  Rust with a patched LLVM via `llvm-config`, not the built-in
  LLVM.

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

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Add `x.sh` and `x.ps1` shell scripts]
  (rust-lang/rust#99992)
- [compiletest: use target cfg instead of hard-coded tables]
  (rust-lang/rust#100260)
- [Use object instead of LLVM for reading bitcode from rlibs]
  (rust-lang/rust#98100)
- [Enable MIR inlining for optimized compilations]
  (rust-lang/rust#91743)
  This provides a 3-10% improvement in compiletimes for real world
  crates. See [perf results]
  (https://perf.rust-lang.org/compare.html?start=aedf78e56b2279cc869962feac5153b6ba7001ed&end=0075bb4fad68e64b6d1be06bf2db366c30bc75e1&stat=instructions:u).
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Iterator has #[must_use] but ExactSizeIterator does not