Const stability checks v2
The const stability system has served us well ever since `const fn` were first stabilized. It's main feature is that it enforces *recursive* validity -- a stable const fn cannot internally make use of unstable const features without an explicit marker in the form of `#[rustc_allow_const_fn_unstable]`. This is done to make sure that we don't accidentally expose unstable const features on stable in a way that would be hard to take back. As part of this, it is enforced that a `#[rustc_const_stable]` can only call `#[rustc_const_stable]` functions. However, some problems have been coming up with increased usage:
- It is baffling that we have to mark private or even unstable functions as `#[rustc_const_stable]` when they are used as helpers in regular stable `const fn`, and often people will rather add `#[rustc_allow_const_fn_unstable]` instead which was not our intention.
- The system has several gaping holes: a private `const fn` without stability attributes whose inherited stability (walking up parent modules) is `#[stable]` is allowed to call *arbitrary* unstable const operations, but can itself be called from stable `const fn`. Similarly, `#[allow_internal_unstable]` on a macro completely bypasses the recursive nature of the check.
Fundamentally, the problem is that we have *three* disjoint categories of functions, and not enough attributes to distinguish them:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
Functions in the first two categories cannot use unstable const features and they can only call functions from the first two categories.
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, all the holes mentioned above have been closed. There's still one potential hole that is hard to avoid, which is when MIR building automatically inserts calls to a particular function in stable functions -- which happens in the panic machinery. Those need to be manually marked `#[rustc_const_stable_indirect]` to be sure they follow recursive const stability. But that's a fairly rare and special case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be constified simply by marking it as `const fn`, and it will then be const-callable from stable `const fn` and subject to recursive const stability requirements. If it is publicly reachable (which implies it cannot be unmarked), it will be const-unstable under the same feature gate. Only if the function ever becomes `#[stable]` does it need a `#[rustc_const_unstable]` or `#[rustc_const_stable]` marker to decide if this should also imply const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to use unstable const lang features (including intrinsics), or (b) `#[stable]` functions that are not yet intended to be const-stable. Adding `#[rustc_const_stable]` is only needed for functions that are actually meant to be directly callable from stable const code. `#[rustc_const_stable_indirect]` is used to mark intrinsics as const-callable and for `#[rustc_const_unstable]` functions that are actually called from other, exposed-on-stable `const fn`. No other attributes are required.
Also see the updated dev-guide at https://github.com/rust-lang/rustc-dev-guide/pull/2098.
I think in the future we may want to tweak this further, so that in the hopefully common case where a public function's const-stability just exactly mirrors its regular stability, we never have to add any attribute. But right now, once the function is stable this requires `#[rustc_const_stable]`.
### Open question
There is one point I could see we might want to do differently, and that is putting `#[rustc_const_unstable]` functions (but not intrinsics) in category 2 by default, and requiring an extra attribute for `#[rustc_const_not_exposed_on_stable]` or so. This would require a bunch of extra annotations, but would have the advantage that turning a `#[rustc_const_unstable]` into `#[rustc_const_stable]` will never change the way the function is const-checked. Currently, we often discover in the const stabilization PR that a function needs some other unstable const things, and then we rush to quickly deal with that. In this alternative universe, we'd work towards getting rid of the `rustc_const_not_exposed_on_stable` before stabilization, and once that is done stabilization becomes a trivial matter. `#[rustc_const_stable_indirect]` would then only be used for intrinsics.
I think I like this idea, but might want to do it in a follow-up PR, as it will need a whole bunch of annotations in the standard library. Also, we probably want to convert all const intrinsics to the "new" form (`#[rustc_intrinsic]` instead of an `extern` block) before doing this to avoid having to deal with two different ways of declaring intrinsics.
Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`
Part of https://github.com/rust-lang/rust/issues/129815 (but not finished since this is not yet sufficient to safely let us expose `const fn` from hashbrown)
Fixes https://github.com/rust-lang/rust/issues/131073 by making it so that const-stable functions are always stable
try-job: test-various
Fundamentally, we have *three* disjoint categories of functions:
1. const-stable functions
2. private/unstable functions that are meant to be callable from const-stable functions
3. functions that can make use of unstable const features
This PR implements the following system:
- `#[rustc_const_stable]` puts functions in the first category. It may only be applied to `#[stable]` functions.
- `#[rustc_const_unstable]` by default puts functions in the third category. The new attribute `#[rustc_const_stable_indirect]` can be added to such a function to move it into the second category.
- `const fn` without a const stability marker are in the second category if they are still unstable. They automatically inherit the feature gate for regular calls, it can now also be used for const-calls.
Also, several holes in recursive const stability checking are being closed.
There's still one potential hole that is hard to avoid, which is when MIR
building automatically inserts calls to a particular function in stable
functions -- which happens in the panic machinery. Those need to *not* be
`rustc_const_unstable` (or manually get a `rustc_const_stable_indirect`) to be
sure they follow recursive const stability. But that's a fairly rare and special
case so IMO it's fine.
The net effect of this is that a `#[unstable]` or unmarked function can be
constified simply by marking it as `const fn`, and it will then be
const-callable from stable `const fn` and subject to recursive const stability
requirements. If it is publicly reachable (which implies it cannot be unmarked),
it will be const-unstable under the same feature gate. Only if the function ever
becomes `#[stable]` does it need a `#[rustc_const_unstable]` or
`#[rustc_const_stable]` marker to decide if this should also imply
const-stability.
Adding `#[rustc_const_unstable]` is only needed for (a) functions that need to
use unstable const lang features (including intrinsics), or (b) `#[stable]`
functions that are not yet intended to be const-stable. Adding
`#[rustc_const_stable]` is only needed for functions that are actually meant to
be directly callable from stable const code. `#[rustc_const_stable_indirect]` is
used to mark intrinsics as const-callable and for `#[rustc_const_unstable]`
functions that are actually called from other, exposed-on-stable `const fn`. No
other attributes are required.
Avoid using imports in thread_local_inner! in static
Fixes#131863 for wasm targets
All other macros were done in #131866, but this sub module is missed.
r? `@jieyouxu`
AIX: use /dev/urandom for random implementation
On AIX, we can poll `/dev/urandom` for cryptographically secure random output to implement `fill_bytes` because we don't have equivalent syscalls like other platforms. https://www.ibm.com/docs/en/aix/7.3?topic=files-random-urandom-devices
[musl] use posix_spawn if a directory change was requested
Currently, not all libcs have the `posix_spawn_file_actions_addchdir_np` symbol available to them. So we attempt to do a weak symbol lookup for that function. But that only works if libc is a dynamic library -- with statically linked musl binaries the symbol lookup would never work, so we would never be able to use it even if the musl in use supported the symbol.
Now that Rust has a minimum musl version of 1.2.3, all supported musl versions now include this symbol, so we can unconditionally expect it to be there. This symbol was added to libc in https://github.com/rust-lang/libc/pull/3949 -- use it here.
I couldn't find any tests for whether the posix_spawn path is used, but I've verified with cargo-nextest that this change works. This is a substantial improvement to nextest's performance with musl. On my workstation with a Ryzen 7950x, against https://github.com/clap-rs/clap at
61f5ee514f8f60ed8f04c6494bdf36c19e7a8126:
Before:
```
Summary [ 1.071s] 879 tests run: 879 passed, 0 skipped
```
After:
```
Summary [ 0.392s] 879 tests run: 879 passed, 0 skipped
```
Fixes#99740.
try-job: dist-various-1
try-job: dist-various-2
Remove the `Arc` rt::init allocation for thread info
Removes an allocation pre-main by just not storing anything in std:🧵:Thread for the main thread.
- The thread name can just be a hard coded literal, as was done in #123433.
- Storing ThreadId and Parker in a static that is initialized once at startup. This uses SyncUnsafeCell and MaybeUninit as this is quite performance critical and we don't need synchronization or to store a tag value and possibly leave in a panic.
Currently, not all libcs have the `posix_spawn_file_actions_addchdir_np` symbol
available to them. So we attempt to do a weak symbol lookup for that function.
But that only works if libc is a dynamic library -- with statically linked musl
binaries the symbol lookup would never work, so we would never be able to use it
even if the musl in use supported the symbol.
Now that Rust has a minimum musl version of 1.2.3, all supported musl versions
now include this symbol, so we can unconditionally expect it to be there. This
symbol was added to libc in https://github.com/rust-lang/libc/pull/3949 -- use
it here.
I couldn't find any tests for whether the posix_spawn path is used, but I've
verified with cargo-nextest that this change works. This is a substantial
improvement to nextest's performance with musl. On my workstation with a Ryzen
7950x, against https://github.com/clap-rs/clap at
61f5ee514f8f60ed8f04c6494bdf36c19e7a8126:
Before:
```
Summary [ 1.071s] 879 tests run: 879 passed, 0 skipped
```
After:
```
Summary [ 0.392s] 879 tests run: 879 passed, 0 skipped
```
Fixes#99740.
stabilize Strict Provenance and Exposed Provenance APIs
Given that [RFC 3559](https://rust-lang.github.io/rfcs/3559-rust-has-provenance.html) has been accepted, t-lang has approved the concept of provenance to exist in the language. So I think it's time that we stabilize the strict provenance and exposed provenance APIs, and discuss provenance explicitly in the docs:
```rust
// core::ptr
pub const fn without_provenance<T>(addr: usize) -> *const T;
pub const fn dangling<T>() -> *const T;
pub const fn without_provenance_mut<T>(addr: usize) -> *mut T;
pub const fn dangling_mut<T>() -> *mut T;
pub fn with_exposed_provenance<T>(addr: usize) -> *const T;
pub fn with_exposed_provenance_mut<T>(addr: usize) -> *mut T;
impl<T: ?Sized> *const T {
pub fn addr(self) -> usize;
pub fn expose_provenance(self) -> usize;
pub fn with_addr(self, addr: usize) -> Self;
pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self;
}
impl<T: ?Sized> *mut T {
pub fn addr(self) -> usize;
pub fn expose_provenance(self) -> usize;
pub fn with_addr(self, addr: usize) -> Self;
pub fn map_addr(self, f: impl FnOnce(usize) -> usize) -> Self;
}
impl<T: ?Sized> NonNull<T> {
pub fn addr(self) -> NonZero<usize>;
pub fn with_addr(self, addr: NonZero<usize>) -> Self;
pub fn map_addr(self, f: impl FnOnce(NonZero<usize>) -> NonZero<usize>) -> Self;
}
```
I also did a pass over the docs to adjust them, because this is no longer an "experiment". The `ptr` docs now discuss the concept of provenance in general, and then they go into the two families of APIs for dealing with provenance: Strict Provenance and Exposed Provenance. I removed the discussion of how pointers also have an associated "address space" -- that is not actually tracked in the pointer value, it is tracked in the type, so IMO it just distracts from the core point of provenance. I also adjusted the docs for `with_exposed_provenance` to make it clear that we cannot guarantee much about this function, it's all best-effort.
There are two unstable lints associated with the strict_provenance feature gate; I moved them to a new [strict_provenance_lints](https://github.com/rust-lang/rust/issues/130351) feature since I didn't want this PR to have an even bigger FCP. ;)
`@rust-lang/opsem` Would be great to get some feedback on the docs here. :)
Nominating for `@rust-lang/libs-api.`
Part of https://github.com/rust-lang/rust/issues/95228.
[FCP comment](https://github.com/rust-lang/rust/pull/130350#issuecomment-2395114536)
replace STATX_ALL with (STATX_BASIC_STATS | STATX_BTIME) as former is deprecated
STATX_ALL was deprecated in 581701b7ef and suggested to use equivalent (STATX_BASIC_STATS | STATX_BTIME) combination, to prevent future surprises.
Update `use` keyword docs to describe precise capturing
I noticed that the standard library keyword docs for the `use` keyword haven't been updated yet to describe the new precise capturing syntax.
Make `profiler_builtins` an optional dependency of sysroot, not std
This avoids unnecessary rebuilds of std (and the compiler) when `build.profiler` is toggled off or on.
Fixes#131812.
---
Background: The `profiler_builtins` crate has been an optional dependency of std (behind a cargo feature) ever since it was added back in #42433. But as far as I can tell that has only ever been a convenient way to force the crate to be built, not a genuine dependency.
The side-effect of this false dependency is that toggling `build.profiler` causes a rebuild of std and the compiler, which shouldn't be necessary. This PR therefore makes `profiler_builtins` an optional dependency of the dummy sysroot crate (#108865), rather than a dependency of std.
What makes this change so small is that all of the necessary infrastructure already exists. Previously, bootstrap would enable the `profiler` feature on the sysroot crate, which would forward that feature to std. Now, enabling that feature directly enables sysroot's `profiler_builtins` dependency instead.
---
I believe this is more of a bootstrap change than a libs change, so tentatively:
r? bootstrap
- Since in almost all cases, there will only be 1 UEFI shell, share the
shell handle between all functions that require it.
Signed-off-by: Ayush Singh <ayush@beagleboard.org>
Rollup of 3 pull requests
Successful merges:
- #126207 (std::unix::stack_overflow::drop_handler addressing todo through libc …)
- #131864 (Never emit `vptr` for empty/auto traits)
- #131870 (compiletest: Store test collection context/state in two structs)
r? `@ghost`
`@rustbot` modify labels: rollup
Abstract the state type for futexes
In the same way that we expose `SmallAtomic` and `SmallPrimitive` to allow Windows to use a value other than an `AtomicU32` for its futex state, switch the primary futex state type from `AtomicU32` to `futex::Futex`. The `futex::Futex` type should be usable as an atomic value with underlying primitive type equal to `futex::Primitive`. (`SmallAtomic` is also renamed to `SmallFutex`).
This allows supporting the futex API on systems where the underlying kernel futex implementation requires more user state than simply an `AtomicU32`.
All in-tree futex implementations simply define {`Futex`,`Primitive`} directly as {`AtomicU32`,`u32`}.
Avoid use imports in `thread_local_inner!`
Previously, the use imports in `thread_local_inner!` can shadow user-provided types or type aliases of the names `Storage`, `EagerStorage`, `LocalStorage` and `LocalKey`. This PR fixes that by dropping the use imports and instead refer to the std-internal types via fully qualified paths. A basic test is added to ensure `thread_local!`s with static decls with type names that match the aforementioned std-internal type names can successfully compile.
Fixes#131863.
Bump libc to 0.2.161
Bumps libc to the latest release version 0.2.161 which
- includes libc support for the tier 3 RTEMS target
- fixes segfaults on 32-bit FreeBSD targets
- gets musl's `posix_spawn_file_actions_addchdir_np` for some spawn opts
Various fixes for Xous
This patchset includes several fixes for Xous that have crept in over the last few months:
* The `adjust_process()` syscall was incorrect
* Warnings have started appearing in `alloc` -- adopt the same approach as wasm, until wasm figures out a workaround
* Dead code warnings have appeared in the networking code. Add `allow(dead_code)` as these structs are used as IPC values
* Add support for `args` and `env`, which have been useful for running tests
* Update `unwinding` to `0.2.3` which fixes the recent regression due to changes in `asm!()` code
In the same way that we expose SmallAtomic and SmallPrimitive to allow
Windows to use a value other than an AtomicU32 for its futex state, this
patch switches the primary futex state type from AtomicU32 to
futex::Atomic. The futex::Atomic type should be usable as an atomic
value with underlying primitive type equal to futex::Primitive.
This allows supporting the futex API on systems where the underlying
kernel futex implementation requires more state than simply an
AtomicU32.
All in-tree futex implementations simply define {Atomic,Primitive}
directly as {AtomicU32,u32}.
uefi: Implement getcwd and chdir
- Using EFI Shell Protocol. These functions do not make much sense unless a shell is present.
- Return the exe dir in case shell protocol is missing.
r? `@joboet`
