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Mitigate `#[align]` name resolution ambiguity regression with a rename
Mitigates beta regression rust-lang/rust#143834 after a beta backport.
### Background on the beta regression
The name resolution regression arises due to rust-lang/rust#142507 adding a new feature-gated built-in attribute named `#[align]`. However, unfortunately even [introducing new feature-gated unstable built-in attributes can break user code](https://www.github.com/rust-lang/rust/issues/134963) such as
```rs
macro_rules! align {
() => {
/* .. */
};
}
pub(crate) use align; // `use` here becomes ambiguous
```
### Mitigation approach
This PR renames `#[align]` to `#[rustc_align]` to mitigate the beta regression by:
1. Undoing the introduction of a new built-in attribute with a common name, i.e. `#[align]`.
2. Renaming `#[align]` to `#[rustc_align]`. The renamed attribute being `rustc_align` will not introduce new stable breakages, as attributes beginning with `rustc` are reserved and perma-unstable. This does mean existing nightly code using `fn_align` feature will additionally need to specify `#![feature(rustc_attrs)]`.
This PR is very much a short-term mitigation to alleviate time pressure from having to fully fix the current limitation of inevitable name resolution regressions that would arise from adding any built-in attributes. Long-term solutions are discussed in [#t-lang > namespacing macro attrs to reduce conflicts with new adds](https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/namespacing.20macro.20attrs.20to.20reduce.20conflicts.20with.20new.20adds/with/529249622).
### Alternative mitigation options
[Various mitigation options were considered during the compiler triage meeting](https://github.com/rust-lang/rust/issues/143834#issuecomment-3084415277), and those consideration are partly reproduced here:
- Reverting the PR doesn't seem very minimal/trivial, and carries risks of its own.
- Rename to a less-common but aim-to-stabilization name is itself not safe nor convenient, because (1) that risks introducing new regressions (i.e. ambiguity against the new name), and (2) lang would have to FCP the new name hastily for the mitigation to land timely and have a chance to be backported. This also makes the path towards stabilization annoying.
- Rename the attribute to a rustc attribute, which will be perma-unstable and does not cause new ambiguities in stable code.
- This alleviates the time pressure to address *this* regression, or for lang to have to rush an FCP for some new name that can still break user code.
- This avoids backing out a whole implementation.
### Review advice
This PR is best reviewed commit-by-commit.
- Commit 1 adds a test `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` which demonstrates the current name resolution regression re. `align`. This test fails against current master.
- Commit 2 carries out the renames and test reblesses. Notably, commit 2 will cause `tests/ui/attributes/fn-align-nameres-ambiguity-143834.rs` to change from fail (nameres regression) to pass.
This PR, if the approach still seems acceptable, will need a beta-backport to address the beta regression.
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From `#[align]` -> `#[rustc_align]`. Attributes starting with `rustc`
are always perma-unstable and feature-gated by `feature(rustc_attrs)`.
See regression RUST-143834.
For the underlying problem where even introducing new feature-gated
unstable built-in attributes can break user code such as
```rs
macro_rules! align {
() => {
/* .. */
};
}
pub(crate) use align; // `use` here becomes ambiguous
```
refer to RUST-134963.
Since the `#[align]` attribute is still feature-gated by
`feature(fn_align)`, we can rename it as a mitigation. Note that
`#[rustc_align]` will obviously mean that current unstable user code
using `feature(fn_aling)` will need additionally `feature(rustc_attrs)`,
but this is a short-term mitigation to buy time, and is expected to be
changed to a better name with less collision potential.
See
<https://rust-lang.zulipchat.com/#narrow/channel/238009-t-compiler.2Fmeetings/topic/.5Bweekly.5D.202025-07-17/near/529290371>
where mitigation options were considered.
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Add std::hint::spin_loop() to tests
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Specialize sleep_until implementation for unix (except mac)
related tracking issue: https://github.com/rust-lang/rust/issues/113752
Supersedes https://github.com/rust-lang/rust/pull/118480 for the reasons see: https://github.com/rust-lang/rust/issues/113752#issuecomment-2902594469
Replaces the generic catch all implementation with target_os specific ones for: linux/netbsd/freebsd/android/solaris/illumos etc. Other platforms like wasi, macos/ios/tvos/watchos and windows will follow in later separate PR's (once this is merged).
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The clock_nanosleep support is there to allow code using `sleep_until`
to run under Miri. Therefore the implementation is minimal.
- Only the clocks REALTIME and MONOTONIC are supported. The first is supported simply
because it was trivial to add not because it was needed for sleep_until.
- The only supported flag combinations are no flags or TIMER_ABSTIME only.
If an unsupported flag combination or clock is passed in this throws
unsupported.
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Rollup of 14 pull requests
Successful merges:
- rust-lang/rust#142429 (`tests/ui`: A New Order [13/N])
- rust-lang/rust#142514 (Miri: handling of SNaN inputs in `f*::pow` operations)
- rust-lang/rust#143066 (Use let chains in the new solver)
- rust-lang/rust#143090 (Workaround for memory unsafety in third party DLLs)
- rust-lang/rust#143118 (`tests/ui`: A New Order [15/N])
- rust-lang/rust#143159 (Do not freshen `ReError`)
- rust-lang/rust#143168 (`tests/ui`: A New Order [16/N])
- rust-lang/rust#143176 (fix typos and improve clarity in documentation)
- rust-lang/rust#143187 (Add my work email to mailmap)
- rust-lang/rust#143190 (Use the `new` method for `BasicBlockData` and `Statement`)
- rust-lang/rust#143195 (`tests/ui`: A New Order [17/N])
- rust-lang/rust#143196 (Port #[link_section] to the new attribute parsing infrastructure)
- rust-lang/rust#143199 (Re-disable `tests/run-make/short-ice` on Windows MSVC again)
- rust-lang/rust#143219 (Show auto trait and blanket impls for `!`)
r? `@ghost`
`@rustbot` modify labels: rollup
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Miri: handling of SNaN inputs in `f*::pow` operations
fixes [miri/#4286](https://github.com/rust-lang/miri/issues/4286) and related to rust-lang/rust#138062 and [miri/#4208](https://github.com/rust-lang/miri/issues/4208#issue-2879058184).
For the following cases of the powf or powi operations, Miri returns either `1.0` or an arbitrary `NaN`:
- `powf(SNaN, 0.0)`
- `powf(1.0, SNaN)`
- `powi(SNaN, 0)`
Also added a macro in `miri/tests/pass/float.rs` which conveniently checks if both are indeed returned from such an operation.
Made these changes in the rust repo so I could test against stdlib, since these were impacted some time ago and were fixed in rust-lang/rust#138062. Tested with:
```fish
env MIRIFLAGS=-Zmiri-many-seeds ./x miri --no-fail-fast std core coretests -- f32 f64
```
This was successful. This does take a while, so I recommend using `--no-doc` and separate use of `f32` or `f64`
The pr is somewhat split up into 3 main commits, which implement the cases described above. The first commit also introduces the macro, and the last commit is just a global refactor of some things.
r? `@RalfJung`
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Add shims for `gettid`-esque functions
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Various platforms provide a function to return the current OS thread ID,
but they all use a slightly different name. Add shims for these
functions for Apple, FreeBSD, and Windows, with tests to account for
those and a few more platforms that are not yet supported by Miri. The
syscall and extern symbol is included as well on Linux.
These should be useful in general but will also help support printing
the OS thread ID in panic messages [1].
[1]: https://github.com/rust-lang/rust/pull/115746
Squashed commit from Ralf:
try_from_scalar: extend comment
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plus various minor tweaks
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Add SIMD funnel shift and round-to-even intrinsics
This PR adds 3 new SIMD intrinsics
- `simd_funnel_shl` - funnel shift left
- `simd_funnel_shr` - funnel shift right
- `simd_round_ties_even` (vector version of `round_ties_even_fN`)
TODO (future PR): implement `simd_fsh{l,r}` in miri, cg_gcc and cg_clif (it is surprisingly hard to implement without branches, the common tricks that rotate uses doesn't work because we have 2 elements now. e.g, the `-n&31` trick used by cg_gcc to implement rotate doesn't work with this because then `fshl(a, b, 0)` will be `a | b`)
[#t-compiler > More SIMD intrinsics](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/More.20SIMD.20intrinsics/with/522130286)
`@rustbot` label T-compiler T-libs A-intrinsics F-core_intrinsics
r? `@workingjubilee`
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use `#[align]` attribute for `fn_align`
Tracking issue: https://github.com/rust-lang/rust/issues/82232
https://github.com/rust-lang/rfcs/pull/3806 decides to add the `#[align]` attribute for alignment of various items. Right now it's used for functions with `fn_align`, in the future it will get more uses (statics, struct fields, etc.)
(the RFC finishes FCP today)
r? `@ghost`
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Right now it's used for functions with `fn_align`, in the future it will
get more uses (statics, struct fields, etc.)
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Change __rust_no_alloc_shim_is_unstable to be a function
This fixes a long sequence of issues:
1. A customer reported that building for Arm64EC was broken: #138541
2. This was caused by a bug in my original implementation of Arm64EC support, namely that only functions on Arm64EC need to be decorated with `#` but Rust was decorating statics as well.
3. Once I corrected Rust to only decorate functions, I started linking failures where the linker couldn't find statics exported by dylib dependencies. This was caused by the compiler not marking exported statics in the generated DEF file with `DATA`, thus they were being exported as functions not data.
4. Once I corrected the way that the DEF files were being emitted, the linker started failing saying that it couldn't find `__rust_no_alloc_shim_is_unstable`. This is because the MSVC linker requires the declarations of statics imported from other dylibs to be marked with `dllimport` (whereas it will happily link to functions imported from other dylibs whether they are marked `dllimport` or not).
5. I then made a change to ensure that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport`, but the MSVC linker started emitting warnings that `__rust_no_alloc_shim_is_unstable` was marked as `dllimport` but was declared in an obj file. This is a harmless warning which is a performance hint: anything that's marked `dllimport` must be indirected via an `__imp` symbol so I added a linker arg in the target to suppress the warning.
6. A customer then reported a similar warning when using `lld-link` (<https://github.com/rust-lang/rust/pull/140176#issuecomment-2872448443>). I don't think it was an implementation difference between the two linkers but rather that, depending on the obj that the declaration versus uses of `__rust_no_alloc_shim_is_unstable` landed in we would get different warnings, so I suppressed that warning as well: #140954.
7. Another customer reported that they weren't using the Rust compiler to invoke the linker, thus these warnings were breaking their build: <https://github.com/rust-lang/rust/pull/140176#issuecomment-2881867433>. At that point, my original change was reverted (#141024) leaving Arm64EC broken yet again.
Taking a step back, a lot of these linker issues arise from the fact that `__rust_no_alloc_shim_is_unstable` is marked as `extern "Rust"` in the standard library and, therefore, assumed to be a foreign item from a different crate BUT the Rust compiler may choose to generate it either in the current crate, some other crate that will be statically linked in OR some other crate that will by dynamically imported.
Worse yet, it is impossible while building a given crate to know if `__rust_no_alloc_shim_is_unstable` will statically linked or dynamically imported: it might be that one of its dependent crates is the one with an allocator kind set and thus that crate (which is compiled later) will decide depending if it has any dylib dependencies or not to import `__rust_no_alloc_shim_is_unstable` or generate it. Thus, there is no way to know if the declaration of `__rust_no_alloc_shim_is_unstable` should be marked with `dllimport` or not.
There is a simple fix for all this: there is no reason `__rust_no_alloc_shim_is_unstable` must be a static. It needs to be some symbol that must be linked in; thus, it could easily be a function instead. As a function, there is no need to mark it as `dllimport` when dynamically imported which avoids the entire mess above.
There may be a perf hit for changing the `volatile load` to be a `tail call`, so I'm happy to change that part back (although I question what the codegen of a `volatile load` would look like, and if the backend is going to try to use load-acquire semantics).
Build with this change applied BEFORE #140176 was reverted to demonstrate that there are no linking issues with either MSVC or MinGW: <https://github.com/rust-lang/rust/actions/runs/15078657205>
Incidentally, I fixed `tests/run-make/no-alloc-shim` to work with MSVC as I needed it to be able to test locally (FYI for #128602)
r? `@bjorn3`
cc `@jieyouxu`
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Rollup of 12 pull requests
Successful merges:
- rust-lang/rust#141639 (Expose discriminant values in stable_mir)
- rust-lang/rust#142082 (Refactor `rustc_attr_data_structures` documentation)
- rust-lang/rust#142125 (Stabilize "file_lock" feature)
- rust-lang/rust#142236 (Add documentation for `PathBuf`'s `FromIterator` and `Extend` impls)
- rust-lang/rust#142373 (Fix Debug for Location)
- rust-lang/rust#142416 (Assorted bootstrap cleanups (step 2))
- rust-lang/rust#142431 (Add initial version of snapshot tests to bootstrap)
- rust-lang/rust#142450 (Add documentation on top of `rustc_middle/src/query/mod.rs`)
- rust-lang/rust#142528 (clarify `rustc_do_not_const_check` comment)
- rust-lang/rust#142530 (use `if let` guards where possible)
- rust-lang/rust#142561 (Remove an `njn:` comment accidentaly left behind.)
- rust-lang/rust#142566 (Fix `-nopt` CI jobs)
r? `@ghost`
`@rustbot` modify labels: rollup
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diagnostics: do not repeat the entire message in the span label
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add SmallVec test
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Enable Non-determinism of float operations in Miri and change std tests
Links to [#4208](https://github.com/rust-lang/miri/issues/4208) and [#3555](https://github.com/rust-lang/miri/issues/3555) in Miri.
Non-determinism of floating point operations was disabled in rust-lang/rust#137594 because it breaks the tests and doc-tests in core/coretests and std. This PR enables some of them.
This pr includes the following changes:
- Enables the float non-determinism but with a lower relative error of 4ULP instead of 16ULP
- These operations now have a fixed output based on the C23 standard, except the pow operations, this is tracked in [#4286](https://github.com/rust-lang/miri/issues/4286#issue-3010677983)
- Changes tests that made incorrect assumptions about the operations, not to make that assumption anymore (from `assert_eq!` to `assert_approx_eq!`.
- Changed the doctests of the stdlib of these operations to compare against fixed constants instead of `f*::EPSILON`, which now succeed with Miri and `-Zmiri-many-seeds`
- Added a constant `APPROX_DELTA` in `std/tests/floats/f32.rs` which is used for approximation tests, but with a different value when run in Miri. This is to make these tests succeed.
- Added tests in the float tests of Miri to test the C23 behaviour.
Fixes https://github.com/rust-lang/miri/issues/4208
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TB: Add flag to disable the more precise interior mutability tracking
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Update stdarch submodule
Updates the stdarch submodule.
## Merged PRs
- rust-lang/stdarch#1797
- rust-lang/stdarch#1758
- rust-lang/stdarch#1798
- rust-lang/stdarch#1811
- rust-lang/stdarch#1810
- rust-lang/stdarch#1807
- rust-lang/stdarch#1806
- rust-lang/stdarch#1812
- rust-lang/stdarch#1795
- rust-lang/stdarch#1796
- rust-lang/stdarch#1813
- rust-lang/stdarch#1816
- rust-lang/stdarch#1818
- rust-lang/stdarch#1820
- rust-lang/stdarch#1819
r? `@Amanieu`
`@rustbot` label T-libs-api
Closes rust-lang/rust#111137
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use File::lock to implement flock, and add a test for File::lock
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r=traviscross,jieyouxu
Add a new `mismatched-lifetime-syntaxes` lint
The lang-team [discussed this](https://hackmd.io/nf4ZUYd7Rp6rq-1svJZSaQ) and I attempted to [summarize](https://github.com/rust-lang/rust/pull/120808#issuecomment-2701863833) their decision. The summary-of-the-summary is:
- Using two different kinds of syntax for elided lifetimes is confusing. In rare cases, it may even [lead to unsound code](https://github.com/rust-lang/rust/issues/48686)! Some examples:
```rust
// Lint will warn about these
fn(v: ContainsLifetime) -> ContainsLifetime<'_>;
fn(&'static u8) -> &u8;
```
- Matching up references with no lifetime syntax, references with anonymous lifetime syntax, and paths with anonymous lifetime syntax is an exception to the simplest possible rule:
```rust
// Lint will not warn about these
fn(&u8) -> &'_ u8;
fn(&'_ u8) -> &u8;
fn(&u8) -> ContainsLifetime<'_>;
```
- Having a lint for consistent syntax of elided lifetimes will make the [future goal](https://github.com/rust-lang/rust/issues/91639) of warning-by-default for paths participating in elision much simpler.
---
This new lint attempts to accomplish the goal of enforcing consistent syntax. In the process, it supersedes and replaces the existing `elided-named-lifetimes` lint, which means it starts out life as warn-by-default.
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r=workingjubilee
UnsafePinned: also include the effects of UnsafeCell
This tackles https://github.com/rust-lang/rust/issues/137750 by including an `UnsafeCell` in `UnsafePinned`, thus imbuing it with all the usual properties of interior mutability (no `noalias` nor `dereferenceable` on shared refs, special treatment by Miri's aliasing model). The soundness issue is not fixed yet because coroutine lowering does not use `UnsafePinned`.
The RFC said that `UnsafePinned` would not permit mutability on shared references, but since then, https://github.com/rust-lang/rust/issues/137750 has demonstrated that this is not tenable. In the face of those examples, I propose that we do the "obvious" thing and permit shared mutable state inside `UnsafePinned`. This seems loosely consistent with the fact that we allow going from `Pin<&mut T>` to `&T` (where the former can be aliased with other pointers that perform mutation, and hence the same goes for the latter) -- but the `as_ref` example shows that we in fact would need to add this `UnsafeCell` even if we didn't have a safe conversion to `&T`, since for the compiler and Miri, `&T` and `Pin<&T>` are basically the same type.
To make this possible, I had to remove the `Copy` and `Clone` impls for `UnsafePinned`.
Tracking issue: https://github.com/rust-lang/rust/issues/125735
Cc ``@rust-lang/lang`` ``@rust-lang/opsem`` ``@Sky9x``
I don't think this needs FCP since the type is still unstable -- we'll finally decide whether we like this approach when `UnsafePinned` is moved towards stabilization (IOW, this PR is reversible). However, I'd still like to make sure that the lang team is okay with the direction I am proposing here.
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