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change method resolution to constrain hidden types instead of rejecting method candidates #123962

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merged 3 commits into from
Jun 14, 2024

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oli-obk
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@oli-obk oli-obk commented Apr 15, 2024

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}

r? @compiler-errors

fixes #121404

cc #116652

@oli-obk oli-obk added the T-types Relevant to the types team, which will review and decide on the PR/issue. label Apr 15, 2024
@rustbot rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Apr 15, 2024
@oli-obk

This comment was marked as outdated.

bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 15, 2024
Method resolution constrains hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? `@compiler-errors`
@bors

This comment was marked as outdated.

@oli-obk
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oli-obk commented Apr 15, 2024

@rfcbot merge

This allows new code to compile on stable. It is a necessary step towards making the old solver more similar to the new solver (and subsequently unblocking stabilizing impl-trait-in-associated-types). See the PR's main post for an example of the new kind of code that is now accepted

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rfcbot commented Apr 15, 2024

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

Concerns:

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 Apr 15, 2024
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This causes (TAIT) code to break, like what caused that CI failure. Pls update the FCP to include an example of what becomes ambiguous during method probe.

@lcnr lcnr changed the title Method resolution constrains hidden types instead of rejecting method candidates change method resolution to constrain hidden types instead of rejecting method candidates Apr 15, 2024
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please also add a revision for -Znext-solver to the added tests

tests/ui/impl-trait/method-resolution.rs Outdated Show resolved Hide resolved
tests/ui/impl-trait/method-resolution2.rs Show resolved Hide resolved
tests/ui/impl-trait/method-resolution2.rs Outdated Show resolved Hide resolved
tests/ui/impl-trait/method-resolution3.rs Outdated Show resolved Hide resolved
@@ -0,0 +1,29 @@
//! check that we do not unify `Bar<Foo>` with `BAr<u32>`, even though the
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Suggested change
//! check that we do not unify `Bar<Foo>` with `BAr<u32>`, even though the
//! check that we do not unify `Bar<Foo>` with `Bar<u32>`, even though the

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not resolved, also this comment feels outdated 🤔 isn't the cause here that the Bar<u32> impl does not define Foo?

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I added more tests to cover the case where it actually defines Foo

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But it is also a breaking change, since &self and &mut self method calls on recursive RPIT function calls now constrain the hidden type to &_ and &mut _ respectively. This is not what users really expect or want from this, but there's way around this.

This is concerning to me and I would prefer us to outright error of ambiguity here than constrain incorrectly.

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oli-obk commented Apr 15, 2024

This is concerning to me and I would prefer us to outright error of ambiguity here than constrain incorrectly.

That's not easy to do in the old solver, and likely impossible to do without major downsides. While we could attempt to move the initial method probing into a canonical query, that would mess with inference as we would not have access to the trait bounds on infer vars anymore.

Note that ne new solver handles this correctly

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oli-obk commented Apr 15, 2024

@bors try

bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 15, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

But it is also a breaking change, since `&self` and `&mut self` method calls on recursive RPIT function calls now constrain the hidden type to `&_` and `&mut _` respectively. This is not what users really expect or want from this, but there's way around this.

r? `@compiler-errors`

fixes  rust-lang#121404

cc rust-lang#116652
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bors commented Apr 15, 2024

⌛ Trying commit af980d5 with merge fe30d25...

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jackh726 commented Apr 15, 2024

This is concerning to me and I would prefer us to outright error of ambiguity here than constrain incorrectly.

That's not easy to do in the old solver, and likely impossible to do without major downsides. While we could attempt to move the initial method probing into a canonical query, that would mess with inference as we would not have access to the trait bounds on infer vars anymore.

Note that ne new solver handles this correctly

The test I'm focusing on here is tests/ui/impl-trait/method-resolution4.rs. Today, this works exactly as I would expect on stable. With both this PR and with -Znext-solver, it fails. So, this is not a case where I think the new solver behaves as expected. (Similar with tests/ui/type-alias-impl-trait/method_resolution_trait_method_from_opaque.rs).

The problem I have is: if we make this change and break these cases today, we can't in the future unbreak these cases in the future in a backwards-compatible manner I think, even though as we've both said this is not what users expect.

I think it would be good if you can make a separate PR just adding the tests, so we can more clearly see what would be changing in the future.

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I actually do feel strongly about this, so I'm going to go ahead and raise a concern.

@rfcbot concern unexpected-self-constraint

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bors commented Apr 15, 2024

☀️ Try build successful - checks-actions
Build commit: fe30d25 (fe30d255593ff5176e4ada5fb82b6b6276de3f85)

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oli-obk commented Apr 15, 2024

@craterbot check

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👌 Experiment pr-123962 created and queued.
🤖 Automatically detected try build fe30d25
🔍 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

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oli-obk commented Jun 13, 2024

@bors r=lcnr

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bors commented Jun 13, 2024

📌 Commit 9cf60ee has been approved by lcnr

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 Jun 13, 2024
fmease added a commit to fmease/rust that referenced this pull request Jun 13, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? `@compiler-errors`

fixes  rust-lang#121404

cc rust-lang#116652
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jun 13, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ``@compiler-errors``

fixes  rust-lang#121404

cc rust-lang#116652
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 13, 2024
…iaskrgr

Rollup of 7 pull requests

Successful merges:

 - rust-lang#121216 (Always emit `native-static-libs` note, even if it is empty)
 - rust-lang#122613 (Don't build a broken/untested profiler runtime on mingw targets)
 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126399 (extend the check for LLVM build)

Failed merges:

 - rust-lang#126388 (const-eval: make lint scope computation consistent)

r? `@ghost`
`@rustbot` modify labels: rollup
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jun 13, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ```@compiler-errors```

fixes  rust-lang#121404

cc rust-lang#116652
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 13, 2024
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#121216 (Always emit `native-static-libs` note, even if it is empty)
 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126285 (`UniqueRc`: support allocators and `T: ?Sized`.)
 - rust-lang#126315 (Add pub struct with allow(dead_code) into worklist)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126399 (extend the check for LLVM build)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 13, 2024
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#121216 (Always emit `native-static-libs` note, even if it is empty)
 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126285 (`UniqueRc`: support allocators and `T: ?Sized`.)
 - rust-lang#126315 (Add pub struct with allow(dead_code) into worklist)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126399 (extend the check for LLVM build)

r? `@ghost`
`@rustbot` modify labels: rollup
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jun 13, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ````@compiler-errors````

fixes  rust-lang#121404

cc rust-lang#116652
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 13, 2024
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#121216 (Always emit `native-static-libs` note, even if it is empty)
 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126285 (`UniqueRc`: support allocators and `T: ?Sized`.)
 - rust-lang#126315 (Add pub struct with allow(dead_code) into worklist)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126399 (extend the check for LLVM build)
 - rust-lang#126436 (Reduce rustdoc GUI tests flakyness)

r? `@ghost`
`@rustbot` modify labels: rollup
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jun 13, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? `````@compiler-errors`````

fixes  rust-lang#121404

cc rust-lang#116652
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 13, 2024
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#121216 (Always emit `native-static-libs` note, even if it is empty)
 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126285 (`UniqueRc`: support allocators and `T: ?Sized`.)
 - rust-lang#126315 (Add pub struct with allow(dead_code) into worklist)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126399 (extend the check for LLVM build)

r? `@ghost`
`@rustbot` modify labels: rollup
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this pull request Jun 14, 2024
change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ``````@compiler-errors``````

fixes  rust-lang#121404

cc rust-lang#116652
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 14, 2024
…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#124884 (place explicit lifetime bound after generic param)
 - rust-lang#126244 (Update fuchsia commit, and SDK to 21.20240610.2.1)
 - rust-lang#126270 (Migrate run make const fn mir)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126343 (Remove some msys2 utils)
 - rust-lang#126351 (std::unix::fs::link using direct linkat call for Solaris.)
 - rust-lang#126368 (Remove some unnecessary crate dependencies.)
 - rust-lang#126386 (Migrate `run-make/allow-non-lint-warnings-cmdline` to `rmake.rs`)
 - rust-lang#126449 (Fill out missing Windows support information)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Jun 14, 2024
…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#123962 (change method resolution to constrain hidden types instead of rejecting method candidates)
 - rust-lang#126244 (Update fuchsia commit, and SDK to 21.20240610.2.1)
 - rust-lang#126270 (Migrate run make const fn mir)
 - rust-lang#126320 (Avoid ICES after reporting errors on erroneous patterns)
 - rust-lang#126449 (Fill out missing Windows support information)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 0468462 into rust-lang:master Jun 14, 2024
6 checks passed
@rustbot rustbot added this to the 1.81.0 milestone Jun 14, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Jun 14, 2024
Rollup merge of rust-lang#123962 - oli-obk:define_opaque_types5, r=lcnr

change method resolution to constrain hidden types instead of rejecting method candidates

Some of these are in probes and may affect inference. This is therefore a breaking change.

This allows new code to compile on stable:

```rust
trait Trait {}

impl Trait for u32 {}

struct Bar<T>(T);

impl Bar<u32> {
    fn foo(self) {}
}

fn foo(x: bool) -> Bar<impl Sized> {
    if x {
        let x = foo(false);
        x.foo();
        //^ this used to not find the `foo` method, because while we did equate `x`'s type with possible candidates, we didn't allow opaque type inference while doing so
    }
    todo!()
}
```

r? ```````@compiler-errors```````

fixes  rust-lang#121404

cc rust-lang#116652
tmeijn pushed a commit to tmeijn/dotfiles that referenced this pull request Sep 11, 2024
This MR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [rust](https://github.com/rust-lang/rust) | minor | `1.80.1` -> `1.81.0` |

MR created with the help of [el-capitano/tools/renovate-bot](https://gitlab.com/el-capitano/tools/renovate-bot).

**Proposed changes to behavior should be submitted there as MRs.**

---

### Release Notes

<details>
<summary>rust-lang/rust (rust)</summary>

### [`v1.81.0`](https://github.com/rust-lang/rust/blob/HEAD/RELEASES.md#Version-1810-2024-09-05)

[Compare Source](rust-lang/rust@1.80.1...1.81.0)

\==========================

<a id="1.81.0-Language"></a>

## Language

-   [Abort on uncaught panics in `extern "C"` functions.](rust-lang/rust#116088)
-   [Fix ambiguous cases of multiple `&` in elided self lifetimes.](rust-lang/rust#117967)
-   [Stabilize `#[expect]` for lints (RFC 2383),](rust-lang/rust#120924) like `#[allow]` with a warning if the lint is *not* fulfilled.
-   [Change method resolution to constrain hidden types instead of rejecting method candidates.](rust-lang/rust#123962)
-   [Bump `elided_lifetimes_in_associated_constant` to deny.](rust-lang/rust#124211)
-   [`offset_from`: always allow pointers to point to the same address.](rust-lang/rust#124921)
-   [Allow constraining opaque types during subtyping in the trait system.](rust-lang/rust#125447)
-   [Allow constraining opaque types during various unsizing casts.](rust-lang/rust#125610)
-   [Deny keyword lifetimes pre-expansion.](rust-lang/rust#126762)

<a id="1.81.0-Compiler"></a>

## Compiler

-   [Make casts of pointers to trait objects stricter.](rust-lang/rust#120248)
-   [Check alias args for well-formedness even if they have escaping bound vars.](rust-lang/rust#123737)
-   [Deprecate no-op codegen option `-Cinline-threshold=...`.](rust-lang/rust#124712)
-   [Re-implement a type-size based limit.](rust-lang/rust#125507)
-   [Properly account for alignment in `transmute` size checks.](rust-lang/rust#125740)
-   [Remove the `box_pointers` lint.](rust-lang/rust#126018)
-   [Ensure the interpreter checks bool/char for validity when they are used in a cast.](rust-lang/rust#126265)
-   [Improve coverage instrumentation for functions containing nested items.](rust-lang/rust#127199)
-   Target changes:
    -   [Add Tier 3 `no_std` Xtensa targets:](rust-lang/rust#125141) `xtensa-esp32-none-elf`, `xtensa-esp32s2-none-elf`, `xtensa-esp32s3-none-elf`
    -   [Add Tier 3 `std` Xtensa targets:](rust-lang/rust#126380) `xtensa-esp32-espidf`, `xtensa-esp32s2-espidf`, `xtensa-esp32s3-espidf`
    -   [Add Tier 3 i686 Redox OS target:](rust-lang/rust#126192) `i686-unknown-redox`
    -   [Promote `arm64ec-pc-windows-msvc` to Tier 2.](rust-lang/rust#126039)
    -   [Promote `loongarch64-unknown-linux-musl` to Tier 2 with host tools.](rust-lang/rust#126298)
    -   [Enable full tools and profiler for LoongArch Linux targets.](rust-lang/rust#127078)
    -   [Unconditionally warn on usage of `wasm32-wasi`.](rust-lang/rust#126662) (see compatibility note below)
    -   Refer to Rust's \[platform support page]\[platform-support-doc] for more information on Rust's tiered platform support.

<a id="1.81.0-Libraries"></a>

## Libraries

-   [Split core's `PanicInfo` and std's `PanicInfo`.](rust-lang/rust#115974) (see compatibility note below)
-   [Generalize `{Rc,Arc}::make_mut()` to unsized types.](rust-lang/rust#116113)
-   [Replace sort implementations with stable `driftsort` and unstable `ipnsort`.](rust-lang/rust#124032) All `slice::sort*` and `slice::select_nth*` methods are expected to see significant performance improvements. See the [research project](https://github.com/Voultapher/sort-research-rs) for more details.
-   [Document behavior of `create_dir_all` with respect to empty paths.](rust-lang/rust#125112)
-   [Fix interleaved output in the default panic hook when multiple threads panic simultaneously.](rust-lang/rust#127397)

<a id="1.81.0-Stabilized-APIs"></a>

## Stabilized APIs

-   [`core::error`](https://doc.rust-lang.org/stable/core/error/index.html)
-   [`hint::assert_unchecked`](https://doc.rust-lang.org/stable/core/hint/fn.assert_unchecked.html)
-   [`fs::exists`](https://doc.rust-lang.org/stable/std/fs/fn.exists.html)
-   [`AtomicBool::fetch_not`](https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicBool.html#method.fetch_not)
-   [`Duration::abs_diff`](https://doc.rust-lang.org/stable/core/time/struct.Duration.html#method.abs_diff)
-   [`IoSlice::advance`](https://doc.rust-lang.org/stable/std/io/struct.IoSlice.html#method.advance)
-   [`IoSlice::advance_slices`](https://doc.rust-lang.org/stable/std/io/struct.IoSlice.html#method.advance_slices)
-   [`IoSliceMut::advance`](https://doc.rust-lang.org/stable/std/io/struct.IoSliceMut.html#method.advance)
-   [`IoSliceMut::advance_slices`](https://doc.rust-lang.org/stable/std/io/struct.IoSliceMut.html#method.advance_slices)
-   [`PanicHookInfo`](https://doc.rust-lang.org/stable/std/panic/struct.PanicHookInfo.html)
-   [`PanicInfo::message`](https://doc.rust-lang.org/stable/core/panic/struct.PanicInfo.html#method.message)
-   [`PanicMessage`](https://doc.rust-lang.org/stable/core/panic/struct.PanicMessage.html)

These APIs are now stable in const contexts:

-   [`char::from_u32_unchecked`](https://doc.rust-lang.org/stable/core/char/fn.from_u32\_unchecked.html) (function)
-   [`char::from_u32_unchecked`](https://doc.rust-lang.org/stable/core/primitive.char.html#method.from_u32\_unchecked) (method)
-   [`CStr::count_bytes`](https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.count_bytes)
-   [`CStr::from_ptr`](https://doc.rust-lang.org/stable/core/ffi/c_str/struct.CStr.html#method.from_ptr)

<a id="1.81.0-Cargo"></a>

## Cargo

-   [Generated `.cargo_vcs_info.json` is always included, even when `--allow-dirty` is passed.](rust-lang/cargo#13960)
-   [Disallow `package.license-file` and `package.readme` pointing to non-existent files during packaging.](rust-lang/cargo#13921)
-   [Disallow passing `--release`/`--debug` flag along with the `--profile` flag.](rust-lang/cargo#13971)
-   [Remove `lib.plugin` key support in `Cargo.toml`. Rust plugin support has been deprecated for four years and was removed in 1.75.0.](rust-lang/cargo#13902)

<a id="1.81.0-Compatibility-Notes"></a>

## Compatibility Notes

-   Usage of the `wasm32-wasi` target will now issue a compiler warning and request users switch to the `wasm32-wasip1` target instead. Both targets are the same, `wasm32-wasi` is only being renamed, and this [change to the WASI target](https://blog.rust-lang.org/2024/04/09/updates-to-rusts-wasi-targets.html) is being done to enable removing `wasm32-wasi` in January 2025.

-   We have renamed `std::panic::PanicInfo` to `std::panic::PanicHookInfo`. The old name will continue to work as an alias, but will result in a deprecation warning starting in Rust 1.82.0.

    `core::panic::PanicInfo` will remain unchanged, however, as this is now a *different type*.

    The reason is that these types have different roles: `std::panic::PanicHookInfo` is the argument to the [panic hook](https://doc.rust-lang.org/stable/std/panic/fn.set_hook.html) in std context (where panics can have an arbitrary payload), while `core::panic::PanicInfo` is the argument to the [`#[panic_handler]`](https://doc.rust-lang.org/nomicon/panic-handler.html) in no_std context (where panics always carry a formatted *message*). Separating these types allows us to add more useful methods to these types, such as `std::panic::PanicHookInfo::payload_as_str()` and `core::panic::PanicInfo::message()`.

-   The new sort implementations may panic if a type's implementation of [`Ord`](https://doc.rust-lang.org/std/cmp/trait.Ord.html) (or the given comparison function) does not implement a [total order](https://en.wikipedia.org/wiki/Total_order) as the trait requires. `Ord`'s supertraits (`PartialOrd`, `Eq`, and `PartialEq`) must also be consistent. The previous implementations would not "notice" any problem, but the new implementations have a good chance of detecting inconsistencies, throwing a panic rather than returning knowingly unsorted data.

-   [In very rare cases, a change in the internal evaluation order of the trait
    solver may result in new fatal overflow errors.](rust-lang/rust#126128)

<a id="1.81.0-Internal-Changes"></a>

## 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 a Rust-for Linux `auto` CI job to check kernel builds.](rust-lang/rust#125209)

</details>

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