Rollup of 6 pull requests
Successful merges:
- rust-lang/rust#135656 (Add `-Z hint-mostly-unused` to tell rustc that most of a crate will go unused)
- rust-lang/rust#138237 (Get rid of `EscapeDebugInner`.)
- rust-lang/rust#141614 (lint direct use of rustc_type_ir )
- rust-lang/rust#142123 (Implement initial support for timing sections (`--json=timings`))
- rust-lang/rust#142377 (Try unremapping compiler sources)
- rust-lang/rust#142674 (remove duplicate crash test)
r? `@ghost`
`@rustbot` modify labels: rollup
Safer implementation of RepeatN
I've seen the "Use MaybeUninit for RepeatN" commit while reading This Week In Rust and immediately thought about something I've written some time ago - https://github.com/Soveu/repeat_finite/blob/master/src/lib.rs.
Using the fact, that `Option` will find niche in `(T, NonZeroUsize)`, we can construct something that has the same size as `(T, usize)` while completely getting rid of `MaybeUninit`.
This leaves only `unsafe` on `TrustedLen`, which is pretty neat.
Sized Hierarchy: Part I
This patch implements the non-const parts of rust-lang/rfcs#3729. It introduces two new traits to the standard library, `MetaSized` and `PointeeSized`. See the RFC for the rationale behind these traits and to discuss whether this change makes sense in the abstract.
These traits are unstable (as is their constness), so users cannot refer to them without opting-in to `feature(sized_hierarchy)`. These traits are not behind `cfg`s as this would make implementation unfeasible, there would simply be too many `cfg`s required to add the necessary bounds everywhere. So, like `Sized`, these traits are automatically implemented by the compiler.
RFC 3729 describes changes which are necessary to preserve backwards compatibility given the introduction of these traits, which are implemented and as follows:
- `?Sized` is rewritten as `MetaSized`
- `MetaSized` is added as a default supertrait for all traits w/out an explicit sizedness supertrait already.
There are no edition migrations implemented in this, as these are primarily required for the constness parts of the RFC and prior to stabilisation of this (and so will come in follow-up PRs alongside the const parts). All diagnostic output should remain the same (showing `?Sized` even if the compiler sees `MetaSized`) unless the `sized_hierarchy` feature is enabled.
Due to the use of unstable extern types in the standard library and rustc, some bounds in both projects have had to be relaxed already - this is unfortunate but unavoidable so that these extern types can continue to be used where they were before. Performing these relaxations in the standard library and rustc are desirable longer-term anyway, but some bounds are not as relaxed as they ideally would be due to the inability to relax `Deref::Target` (this will be investigated separately).
It is hoped that this is implemented such that it could be merged and these traits could exist "under the hood" without that being observable to the user (other than in any performance impact this has on the compiler, etc). Some details might leak through due to the standard library relaxations, but this has not been observed in test output.
**Notes:**
- Any commits starting with "upstream:" can be ignored, as these correspond to other upstream PRs that this is based on which have yet to be merged.
- This best reviewed commit-by-commit. I've attempted to make the implementation easy to follow and keep similar changes and test output updates together.
- Each commit has a short description describing its purpose.
- This patch is large but it's primarily in the test suite.
- I've worked on the performance of this patch and a few optimisations are implemented so that the performance impact is neutral-to-minor.
- `PointeeSized` is a different name from the RFC just to make it more obvious that it is different from `std::ptr::Pointee` but all the names are yet to be bikeshed anyway.
- `@nikomatsakis` has confirmed [that this can proceed as an experiment from the t-lang side](https://rust-lang.zulipchat.com/#narrow/channel/435869-project-goals/topic/SVE.20and.20SME.20on.20AArch64.20.28goals.23270.29/near/506196491)
- FCP in https://github.com/rust-lang/rust/pull/137944#issuecomment-2912207485Fixesrust-lang/rust#79409.
r? `@ghost` (I'll discuss this with relevant teams to find a reviewer)
std: refactor explanation of `NonNull`
Fixesrust-lang/rust#141933
I cut out the excessive explanation and used an example to explain how to maintain invariance, but I think what is quoted in the *rust reference* in the document needs to be added with a more layman's explanation and example.
(I'm not sure if I deleted too much)
r? `@workingjubilee`
As core uses an extern type (`ptr::VTable`), the default `?Sized` to
`MetaSized` migration isn't sufficient, and some code that previously
accepted `VTable` needs relaxed to continue to accept extern types.
Similarly, the compiler uses many extern types in `rustc_codegen_llvm`
and in the `rustc_middle::ty::List` implementation (`OpaqueListContents`)
some bounds must be relaxed to continue to accept these types.
Unfortunately, due to the current inability to relax `Deref::Target`,
some of the bounds in the standard library are forced to be stricter than
they ideally would be.
more information to Display implementation for BorrowError/BorrowMutError
- The BorrowError/BorrowMutError Debug implementations do not print
anything differently from what the derived implementation does, so we
don't need it.
- This change also adds the location field of
BorrowError/BorrowMutError to the the Display output when it is
present, rewords the error message, and uses the Display trait for
outputting the error message instead of Debug.
Introduce the `MetaSized` and `PointeeSized` traits as supertraits of
`Sized` and initially implement it on everything that currently
implements `Sized` to isolate any changes that simply adding the
traits introduces.
No need to call into fold when the first item is already None,
this avoids some redundant work for empty iterators.
"But it uses Fuse" one might want to protest, but Fuse is specialized
and may call into the inner iterator anyway.
Unimplement unsized_locals
Implements https://github.com/rust-lang/compiler-team/issues/630
Tracking issue here: https://github.com/rust-lang/rust/issues/111942
Note that this just removes the feature, not the implementation, and does not touch `unsized_fn_params`. This is because it is required to support `Box<dyn FnOnce()>: FnOnce()`.
There may be more that should be removed (possibly in follow up prs)
- the `forget_unsized` function and `forget` intrinsic.
- the `unsized_locals` test directory; I've just fixed up the tests for now
- various codegen support for unsized values and allocas
cc ``@JakobDegen`` ``@oli-obk`` ``@Noratrieb`` ``@programmerjake`` ``@bjorn3``
``@rustbot`` label F-unsized_locals
Fixesrust-lang/rust#79409
doc: mention that intrinsics should not be called in user code
Intrinsic functions declared in `std::intrinsics` are an implementation detail and should not be called directly by the user. The compiler explicitly warns against their use in user code:
```
warning: the feature `core_intrinsics` is internal to the compiler or standard library
--> src/lib.rs:1:12
|
1 | #![feature(core_intrinsics)]
| ^^^^^^^^^^^^^^^
|
= note: using it is strongly discouraged
= note: `#[warn(internal_features)]` on by default
```
[**Playground link**]
This PR documents what the compiler warning says: these intrinsics should not be used in user code.
[**Playground link**]: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=1c893b0698291f550bbdde0151fd221b
Intrinsic functions declared in `std::intrinsics` are an implementation
detail and should not be called directly by the user. The compiler
explicitly warns against their use in user code:
```
warning: the feature `core_intrinsics` is internal to the compiler or standard library
--> src/lib.rs:1:12
|
1 | #![feature(core_intrinsics)]
| ^^^^^^^^^^^^^^^
|
= note: using it is strongly discouraged
= note: `#[warn(internal_features)]` on by default
```
[**Playground link**]
This PR documents what the compiler warning says: these intrinsics should
not be called outside the standard library.
[**Playground link**]: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=1c893b0698291f550bbdde0151fd221b
Rollup of 6 pull requests
Successful merges:
- rust-lang/rust#138016 (Added `Clone` implementation for `ChunkBy`)
- rust-lang/rust#141162 (refactor `AttributeGate` and `rustc_attr!` to emit notes during feature checking)
- rust-lang/rust#141474 (Add `ParseMode::Diagnostic` and fix multiline spans in diagnostic attribute lints)
- rust-lang/rust#141947 (Specify that "option-like" enums must be `#[repr(Rust)]` to be ABI-compatible with their non-1ZST field.)
- rust-lang/rust#142252 (Improve clarity of `core::sync::atomic` docs about "Considerations" in regards to CAS operations)
- rust-lang/rust#142337 (miri: add flag to suppress float non-determinism)
r? `@ghost`
`@rustbot` modify labels: rollup
intrinsics: rename min_align_of to align_of
Now that `pref_align_of` is gone (https://github.com/rust-lang/rust/pull/141803), we can give the intrinsic backing `align_of` its proper name.
r? `@workingjubilee` or `@bjorn3`
Tracking the old name of renamed unstable library features
This PR resolves the first problem of rust-lang/rust#141617 : tracking renamed unstable features. The first commit is to add a ui test, and the second one tracks the changes. I will comment on the code for clarification.
r? `@jdonszelmann`
There have been a lot of PR's reviewed by you lately, thanks for your time!
cc `@jyn514`
Lint on fn pointers comparisons in external macros
This PR extends the recently stabilized `unpredictable_function_pointer_comparisons` lint ~~to also lint on `Option<{function pointer}>` and~~ as well as linting in external macros (as to catch `assert_eq!` and others).
```rust
assert_eq!(Some::<FnPtr>(func), Some(func as unsafe extern "C" fn()));
//~^ WARN function pointer comparisons
#[derive(PartialEq, Eq)]
struct A {
f: fn(),
//~^ WARN function pointer comparisons
}
```
Fixes https://github.com/rust-lang/rust/issues/134527
Improve clarity of `core::sync::atomic` docs about "Considerations" in regards to CAS operations
## Motivation
The existing documentation for atomic `fetch_update` (and other similar methods) has a section that reads like so:
> ### Considerations
> This method is not magic; it is not provided by the hardware. It is implemented in
> terms of `AtomicBlah::compare_exchange_weak`, and suffers from the same drawbacks.
> In particular, this method will not circumvent the [ABA Problem].
>
> [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
The wording here seems to imply that the drawbacks being discusses are caused by the *`weak` version* of `compare_exchange`, and that one may avoid those drawbacks by using `compare_exchange` instead. Indeed, a conversation in the `#dark-arts` channel on the Rust community discord based on this interpretation led to this PR.
In reality, the drawbacks are inherent to implementing such an operation based on *any* compare-and-swap style operation, as opposed to an [LL,SC](https://en.wikipedia.org/wiki/Load-link/store-conditional) operation, and they apply equally to `compare_exchange` and `compare_exchange_weak` as well.
## Changes
- Rewords existing Considerations section on `fetch_update` and friends to make clear that the limitations are inherent to an implementation based on any CAS operation, rather than the weak version of `compare_exchange` in particular. New version:
> ### Considerations
>
> This method is not magic; it is not provided by the hardware, and does not act like a
> critical section or mutex.
>
> It is implemented on top of an atomic [compare-and-swap operation], and thus is subject to
> the usual drawbacks of CAS operations. In particular, be careful of the [ABA problem]
> if this atomic integer is an index or more generally if knowledge of only the *bitwise value*
> of the atomic is not in and of itself sufficient to ensure any required preconditions.
>
> [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
> [compare-and-swap operation]: https://en.wikipedia.org/wiki/Compare-and-swap
- Add Considerations to `compare_exchange` and `compare_exchange_weak` which details similar considerations and when they may be relevant. New version:
> ### Considerations
>
> `compare_exchange` is a [compare-and-swap operation] and thus exhibits the usual downsides
> of CAS operations. In particular, a load of the value followed by a successful
> `compare_exchange` with the previous load *does not ensure* that other threads have not
> changed the value in the interim. This is usually important when the *equality* check in
> the `compare_exchange` is being used to check the *identity* of a value, but equality
> does not necessarily imply identity. In this case, `compare_exchange` can lead to the
> [ABA problem].
>
> [ABA Problem]: https://en.wikipedia.org/wiki/ABA_problem
> [compare-and-swap operation]: https://en.wikipedia.org/wiki/Compare-and-swap
Specify that "option-like" enums must be `#[repr(Rust)]` to be ABI-compatible with their non-1ZST field.
Add that the enum must be `#[repr(Rust)]` and not `#[repr(packed)]` or `#[repr(align)]` in order to be ABI-compatible with its null-pointer-optimized field.
The specific rules here were decided on here: https://github.com/rust-lang/rust/pull/130628#issuecomment-2402761599 but `repr` was not mentioned. In practice, only `#[repr(Rust)]` (or no `repr` attribute, which is equivalent) works for this, so add that to the docs.
-----
Restrict to `#[repr(Rust)]` only, since:
* `#[repr(C)]` and the primitive representations (`#[repr(u8)]` etc) definitely disqualify the enum from NPO, since they have defined layouts that store the tag separately to the payload.
* `#[repr(transparent)]` enums are covered two bullet points above this (line 1830), and cannot have multiple variants, so would fail the "The enum has exactly two variants" requirement anyway.
As for `#[repr(align)]`: my current wording that it is completely disallowed may be too strong: it seems like `#[repr(align(<= alignment of T))] enum Foo { X, Y(T) }` currently does still have the same ABI as `T` in practice, though this may not be something we want to promise. (`#[repr(align(> alignment of T))]` definitely disqualifies the enum from being ABI-compatible with T currently).
I added the note about `packed` to match `align`, but `#[repr(packed)]` currently can't be applied to `enum`s at all anyway, so might be unnecessary.
-----
I think this needs T-lang approval?
cc ``````@workingjubilee``````
Faster fmt::Display of 128-bit integers, without unsafe pointer
In followup of #135265, hereby the 128-bit part.
* Batches per 16 instead of 19 digits
* Buffer access as array insteaf of unsafe pointer
* Added test coverage for i128 and u128
r? tgross35 ChrisDenton
Implements `trim_prefix` and `trim_suffix` methods for both `slice` and
`str` types which remove at most one occurrence of a prefix/suffix while
always returning a string/slice (rather than Option), enabling easy
method chaining.
