use strict provenance APIs
The stdlib was adjusted to avoid bare int2ptr casts, but recently some casts of that sort have sneaked back in. Let's fix that. :)
implement ptr.addr() via transmute
As per the discussion in https://github.com/rust-lang/unsafe-code-guidelines/issues/286, the semantics for ptr-to-int transmutes that we are going with for now is to make them strip provenance without exposing it. That's exactly what `ptr.addr()` does! So we can implement `ptr.addr()` via `transmute`. This also means that once https://github.com/rust-lang/rust/pull/97684 lands, Miri can distinguish `ptr.addr()` from `ptr.expose_addr()`, and the following code will correctly be called out as having UB (if permissive provenance mode is enabled, which will become the default once the [implementation is complete](https://github.com/rust-lang/miri/issues/2133)):
```rust
fn main() {
let x: i32 = 3;
let x_ptr = &x as *const i32;
let x_usize: usize = x_ptr.addr();
// Cast back an address that did *not* get exposed.
let ptr = std::ptr::from_exposed_addr::<i32>(x_usize);
assert_eq!(unsafe { *ptr }, 3); //~ ERROR Undefined Behavior: dereferencing pointer failed
}
```
This completes the Miri implementation of the new distinctions introduced by strict provenance. :)
Cc `@Gankra` -- for now I left in your `FIXME(strict_provenance_magic)` saying these should be intrinsics, but I do not necessarily agree that they should be. Or if we have an intrinsic, I think it should behave exactly like the `transmute` does, which makes one wonder why the intrinsic should be needed.
Rollup of 6 pull requests
Successful merges:
- #97609 (Iterate over `maybe_unused_trait_imports` when checking dead trait imports)
- #97688 (test const_copy to make sure bytewise pointer copies are working)
- #97707 (Improve soundness of rustc_data_structures)
- #97731 (Add regresion test for #87142)
- #97735 (Don't generate "Impls on Foreign Types" for std)
- #97737 (Fix pretty printing named bound regions under -Zverbose)
Failed merges:
r? `@ghost`
`@rustbot` modify labels: rollup
Call the OS function to set the main thread's name on program init
Normally, `Thread::spawn` takes care of setting the thread's name, if
one was provided, but since the main thread wasn't created by calling
`Thread::spawn`, we need to call that function in `std::rt::init`.
This is mainly useful for system tools like debuggers and profilers
which might show the thread name to a user. Prior to these changes, gdb
and WinDbg would show all thread names except the main thread's name to
a user. I've validated that this patch resolves the issue for both
debuggers.
Lazily allocate and initialize pthread locks.
Lazily allocate and initialize pthread locks.
This allows {Mutex, Condvar, RwLock}::new() to be const, while still using the platform's native locks for features like priority inheritance and debug tooling. E.g. on macOS, we cannot directly use the (private) APIs that pthread's locks are implemented with, making it impossible for us to use anything other than pthread while still preserving priority inheritance, etc.
This PR doesn't yet make the public APIs const. That's for a separate PR with an FCP.
Tracking issue: https://github.com/rust-lang/rust/issues/93740
Avoid zero-sized allocs in ThinBox if T and H are both ZSTs.
This was surprisingly tricky, and took longer to get right than expected. `ThinBox` is a surprisingly subtle piece of code. That said, in the end, a lot of this was due to overthinking[^overthink] -- ultimately the fix ended up fairly clean and simple.
[^overthink]: Honestly, for a while I was convinced this couldn't be done without allocations or runtime branches in these cases, but that's obviously untrue.
Anyway, as a result of spending all that time debugging, I've extended the tests quite a bit, and also added more debug assertions. Many of these helped for subtle bugs I made in the middle (for example, the alloc/drop tracking is because I ended up double-dropping the value in the case where both were ZSTs), they're arguably a bit of overkill at this point, although I imagine they could help in the future too.
Anyway, these tests cover a wide range of size/align cases, nd fully pass under miri[^1]. They also do some smoke-check asserting that the value has the correct alignment, although in practice it's totally within the compiler's rights to delete these assertions since we'd have already done UB if they get hit. They have more boilerplate than they really need, but it's not *too* bad on a per-test basis.
A notable absence from testing is atypical header types, but at the moment it's impossible to manually implement `Pointee`. It would be really nice to have testing here, since it's not 100% obvious to me that the aligned read/write we use for `H` are correct in the face of arbitrary combinations of `size_of::<H>()`, `align_of::<H>()`, and `align_of::<T>()`. (That said, I spent a while thinking through it and am *pretty* sure it's fine -- I'd just feel... better if we could test some cases for non-ZST headers which have unequal and align).
[^1]: Or at least, they pass under miri if I copy the code and tests into a new crate and run miri on it (after making it less stdlibified).
Fixes#96485.
I'd request review ``@yaahc,`` but I believe you're taking some time away from reviews, so I'll request from the previous PR's reviewer (I think that the context helps, even if the actual change didn't end up being bad here).
r? ``@joshtriplett``
Stabilize `{slice,array}::from_ref`
This PR stabilizes the following APIs as `const` functions in Rust `1.63`:
```rust
// core::array
pub const fn from_ref<T>(s: &T) -> &[T; 1];
// core::slice
pub const fn from_ref<T>(s: &T) -> &[T];
```
Note that the `mut` versions are not stabilized as unique references (`&mut _`) are [unstable in const context].
FCP: https://github.com/rust-lang/rust/issues/90206#issuecomment-1134586665
r? rust-lang/libs-api `@rustbot` label +T-libs-api -T-libs
[unstable in const context]: https://github.com/rust-lang/rust/issues/57349
Improve documentation for constructors of pinned `Box`es
Adds a cross-references between `Box::pin` and `Box::into_pin` (and other related methods, i.e. the equivalent `From` implementation, and the unstable `pin_in` method), in particular now that `into_pin` [was stabilized](https://github.com/rust-lang/rust/pull/97397). The main goal is to further improve visibility of the fact that `Box<T> -> Pin<Box<T>>` conversion exits in the first place, and that `Box::pin(x)` is – essentially – just a convenience function for `Box::into_pin(Box::new(x))`
The motivating context why I think this is important is even experienced Rust users overlooking the existence this kind of conversion, [e.g. in this thread on IRLO](https://internals.rust-lang.org/t/pre-rfc-function-variants/16732/7?u=steffahn); and also the fact that that discussion brought up that there would be a bunch of Box-construction methods "missing" such as e.g. methods with fallible allocation a la "`Box::try_pin`", and similar; while those are in fact *not* necessary, because you can use `Box::into_pin(Box::try_new(x)?)` instead.
I have *not* included explicit mention of methods (e.g. `try_new`) in the docs of stable methods (e.g. `into_pin`). (Referring to unstable API in stable API docs would be bad style IMO.) Stable examples I have in mind with the statement "constructing a (pinned) Box in a different way than with `Box::new`" are things like cloning a `Box`, or `Box::from_raw`. If/when `try_new` would get stabilized, it would become a very good concrete example use-case of `Box::into_pin` IMO.
Revert #96682.
The change was "Show invisible delimiters (within comments) when pretty
printing". It's useful to show these delimiters, but is a breaking
change for some proc macros.
Fixes#97608.
r? ``@petrochenkov``
Add #[rustc_box] and use it inside alloc
This commit adds an alternative content boxing syntax, and uses it inside alloc.
```Rust
#![feature(box_syntax)]
fn foo() {
let foo = box bar;
}
```
is equivalent to
```Rust
#![feature(rustc_attrs)]
fn foo() {
let foo = #[rustc_box] Box::new(bar);
}
```
The usage inside the very performance relevant code in
liballoc is the only remaining relevant usage of box syntax
in the compiler (outside of tests, which are comparatively easy to port).
box syntax was originally designed to be used by all Rust
developers. This introduces a replacement syntax more tailored
to only being used inside the Rust compiler, and with it,
lays the groundwork for eventually removing box syntax.
[Earlier work](https://github.com/rust-lang/rust/pull/87781#issuecomment-894714878) by `@nbdd0121` to lower `Box::new` to `box` during THIR -> MIR building ran into borrow checker problems, requiring the lowering to be adjusted in a way that led to [performance regressions](https://github.com/rust-lang/rust/pull/87781#issuecomment-894872367). The proposed change in this PR lowers `#[rustc_box] Box::new` -> `box` in the AST -> HIR lowering step, which is way earlier in the compiler, and thus should cause less issues both performance wise as well as regarding type inference/borrow checking/etc. Hopefully, future work can move the lowering further back in the compiler, as long as there are no performance regressions.
The change was "Show invisible delimiters (within comments) when pretty
printing". It's useful to show these delimiters, but is a breaking
change for some proc macros.
Fixes#97608.
Additional `*mut [T]` methods
Split out from #94247
This adds the following methods to raw slices that already exist on regular slices
* `*mut [T]::is_empty`
* `*mut [T]::split_at_mut`
* `*mut [T]::split_at_mut_unchecked`
These methods reduce the amount of unsafe code needed to migrate `ChunksMut` and related iterators
to raw slices (#94247)
r? `@m-ou-se`
