Stabilize `impl_trait_projections`
Closes#115659
## TL;DR:
This allows us to mention `Self` and `T::Assoc` in async fn and return-position `impl Trait`, as you would expect you'd be able to.
Some examples:
```rust
#![feature(return_position_impl_trait_in_trait, async_fn_in_trait)]
// (just needed for final tests below)
// ---------------------------------------- //
struct Wrapper<'a, T>(&'a T);
impl Wrapper<'_, ()> {
async fn async_fn() -> Self {
//^ Previously rejected because it returns `-> Self`, not `-> Wrapper<'_, ()>`.
Wrapper(&())
}
fn impl_trait() -> impl Iterator<Item = Self> {
//^ Previously rejected because it mentions `Self`, not `Wrapper<'_, ()>`.
std::iter::once(Wrapper(&()))
}
}
// ---------------------------------------- //
trait Trait<'a> {
type Assoc;
fn new() -> Self::Assoc;
}
impl Trait<'_> for () {
type Assoc = ();
fn new() {}
}
impl<'a, T: Trait<'a>> Wrapper<'a, T> {
async fn mk_assoc() -> T::Assoc {
//^ Previously rejected because `T::Assoc` doesn't mention `'a` in the HIR,
// but ends up resolving to `<T as Trait<'a>>::Assoc`, which does rely on `'a`.
// That's the important part -- the elided trait.
T::new()
}
fn a_few_assocs() -> impl Iterator<Item = T::Assoc> {
//^ Previously rejected for the same reason
[T::new(), T::new(), T::new()].into_iter()
}
}
// ---------------------------------------- //
trait InTrait {
async fn async_fn() -> Self;
fn impl_trait() -> impl Iterator<Item = Self>;
}
impl InTrait for &() {
async fn async_fn() -> Self { &() }
//^ Previously rejected just like inherent impls
fn impl_trait() -> impl Iterator<Item = Self> {
//^ Previously rejected just like inherent impls
[&()].into_iter()
}
}
```
## Technical:
Lifetimes in return-position `impl Trait` (and `async fn`) are duplicated as early-bound generics local to the opaque in order to make sure we are able to substitute any late-bound lifetimes from the function in the opaque's hidden type. (The [dev guide](https://rustc-dev-guide.rust-lang.org/return-position-impl-trait-in-trait.html#aside-opaque-lifetime-duplication) has a small section about why this is necessary -- this was written for RPITITs, but it applies to all RPITs)
Prior to #103491, all of the early-bound lifetimes not local to the opaque were replaced with `'static` to avoid issues where relating opaques caused their *non-captured* lifetimes to be related. This `'static` replacement led to strange and possibly unsound behaviors (https://github.com/rust-lang/rust/issues/61949#issuecomment-508836314) (https://github.com/rust-lang/rust/issues/53613) when referencing the `Self` type alias in an impl or indirectly referencing a lifetime parameter via a projection type (via a `T::Assoc` projection without an explicit trait), since lifetime resolution is performed on the HIR, when neither `T::Assoc`-style projections or `Self` in impls are expanded.
Therefore an error was implemented in #62849 to deny this subtle behavior as a known limitation of the compiler. It was attempted by `@cjgillot` to fix this in #91403, which was subsequently unlanded. Then it was re-attempted to much success (🎉) in #103491, which is where we currently are in the compiler.
The PR above (#103491) fixed this issue technically by *not* replacing the opaque's parent lifetimes with `'static`, but instead using variance to properly track which lifetimes are captured and are not. The PR gated any of the "side-effects" of the PR behind a feature gate (`impl_trait_projections`) presumably to avoid having to involve T-lang or T-types in the PR as well. `@cjgillot` can clarify this if I'm misunderstanding what their intention was with the feature gate.
Since we're not replacing (possibly *invariant*!) lifetimes with `'static` anymore, there are no more soundness concerns here. Therefore, this PR removes the feature gate.
Tests:
* `tests/ui/async-await/feature-self-return-type.rs`
* `tests/ui/impl-trait/feature-self-return-type.rs`
* `tests/ui/async-await/issues/issue-78600.rs`
* `tests/ui/impl-trait/capture-lifetime-not-in-hir.rs`
---
r? cjgillot on the impl (not much, just removing the feature gate)
I'm gonna mark this as FCP for T-lang and T-types.
Simplify some of the logic in the `invalid_reference_casting` lint
This PR simplifies 2 areas of the logic for the `invalid_reference_casting` lint:
- The init detection: we now use the newly added `expr_or_init` function instead of a manual detection
- The ref-to-mut-ptr casting detection logic: I simplified this logic by caring less hardly about the order of the casting operations
Those two simplifications permits us to detect more cases, as can be seen in the test output changes.
Update windows ffi bindings
Bump `windows-bindgen` to version 0.51.1. This brings with it some changes to the generated FFI bindings, but little that affects the code.
One change that does have more of an impact is `SOCKET` being `usize` instead of either `u64` or `u32` (as is used in std's public `SOCKET` type). However, it's now easy enough to abstract over that difference.
Finally I added a few new bindings that are likely to be used in pending PRs, mostly to make sure they're ok with the new metadata.
r? libs
Convert `Into<ExitStatus> for ExitStatusError` to `From<ExitStatusError> for ExitStatus` in `std::process`
Implementing suggestion from https://github.com/rust-lang/rust/issues/84908#issuecomment-912352902:
> I believe the impl on ExitStatusError should be
>
> ```rust
> impl From<ExitStatusError> for ExitStatus
> ```
>
> rather than
>
> ```rust
> impl Into<ExitStatus> for ExitStatusError
> ```
>
> (there is generally never anything implemented as `Into` first, because implementing `From` reflexively provides `Into`)
Implement From<OwnedFd/Handle> for ChildStdin/out/err object
## Summary
Comments in `library/std/src/process.rs` ( ab08639e59 ) indicates that `ChildStdin`, `ChildStdout`, `ChildStderr` implements some traits that are not actually implemented: `FromRawFd`, `FromRawHandle`, and the `From<OwnedFd>/From<OwnedHandle>` from the io_safety feature.
In this PR I implement `FromRawHandle` and `FromRawFd` for those 3 objects.
## Usecase
I have a usecase where those implementations are basically needed. I want to customize
in the `Command::spawn` API how the pipes for the parent/child communications are created (mainly to strengthen the security attributes on them). I can properly setup the pipes,
and the "child" handles can be provided to `Child::spawn` easily using `Stdio::from_raw_handle`. However, there is no way to generate the `ChildStd*` objects from the raw handle of the created name pipe, which would be very useful to still expose the same API
than in other OS (basically a `spawn(...) -> (Child, ChildStdin, ChildStdout, ChildSterr)`, where on windows this is customized), and to for example use `tokio::ChildStdin::from_std` afterwards.
## Questions
* Are those impls OK to add? I have searched to see if those impls were missing on purpose, or if it was just never implemented because never needed. I haven't found any indication on why they couldn't be added, although the user clearly has to be very careful that the handle provided makes sense (i think, mainly that it is in overlapped mode for windows).
* If this change is ok, adding the impls for the io_safety feature would probably be best, or should it be done in another PR?
* I just copy-pasted the `#[stable(...)]` attributes, but the `since` value has to be updated, I'm not sure to which value.
