Add support for `for await` loops
This adds support for `for await` loops. This includes parsing, desugaring in AST->HIR lowering, and adding some support functions to the library.
Given a loop like:
```rust
for await i in iter {
...
}
```
this is desugared to something like:
```rust
let mut iter = iter.into_async_iter();
while let Some(i) = loop {
match core::pin::Pin::new(&mut iter).poll_next(cx) {
Poll::Ready(i) => break i,
Poll::Pending => yield,
}
} {
...
}
```
This PR also adds a basic `IntoAsyncIterator` trait. This is partly for symmetry with the way `Iterator` and `IntoIterator` work. The other reason is that for async iterators it's helpful to have a place apart from the data structure being iterated over to store state. `IntoAsyncIterator` gives us a good place to do this.
I've gated this feature behind `async_for_loop` and opened #118898 as the feature tracking issue.
r? `@compiler-errors`
Exhaustiveness: reveal opaque types properly
Previously, exhaustiveness had no clear policy around opaque types. In this PR I propose the following policy: within the body of an item that defines the hidden type of some opaque type, exhaustiveness checking on a value of that opaque type is performed using the concrete hidden type inferred in this body.
I'm not sure how consistent this is with other operations allowed on opaque types; I believe this will require FCP.
From what I can tell, this doesn't change anything for non-empty types.
The observable changes are:
- when the real type is uninhabited, matches within the defining scopes can now rely on that for exhaustiveness, e.g.:
```rust
#[derive(Copy, Clone)]
enum Void {}
fn return_never_rpit(x: Void) -> impl Copy {
if false {
match return_never_rpit(x) {}
}
x
}
```
- this properly fixes ICEs like https://github.com/rust-lang/rust/issues/117100 that occurred because a same match could have some patterns where the type is revealed and some where it is not.
Bonus subtle point: if `x` is opaque, a match like `match x { ("", "") => {} ... }` will constrain its type ([playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=901d715330eac40339b4016ac566d6c3)). This is not the case for `match x {}`: this will not constain the type, and will only compile if something else constrains the type to be empty.
Fixes https://github.com/rust-lang/rust/issues/117100
r? `@oli-obk`
Edited for precision of the wording
[Included](https://github.com/rust-lang/rust/pull/116821#issuecomment-1813171764) in the FCP on this PR is this rule:
> Within the body of an item that defines the hidden type of some opaque type, exhaustiveness checking on a value of that opaque type is performed using the concrete hidden type inferred in this body.
Refactor AST trait bound modifiers
Instead of having two types to represent trait bound modifiers in the parser / the AST (`parser::ty::BoundModifiers` & `ast::TraitBoundModifier`), only to map one to the other later, just use `parser::ty::BoundModifiers` (moved & renamed to `ast::TraitBoundModifiers`).
The struct type is more extensible and easier to deal with (see [here](https://github.com/rust-lang/rust/pull/119099/files#r1430749981) and [here](https://github.com/rust-lang/rust/pull/119099/files#r1430752116) for context) since it more closely models what it represents: A compound of two kinds of modifiers, constness and polarity. Modeling this as an enum (the now removed `ast::TraitBoundModifier`) meant one had to add a new variant per *combination* of modifier kind, which simply isn't scalable and which lead to a lot of explicit non-DRY matches.
NB: `hir::TraitBoundModifier` being an enum is fine since HIR doesn't need to worry representing invalid modifier kind combinations as those get rejected during AST validation thereby immensely cutting down the number of possibilities.
On LLVM 18 we get slightly different arguments here, so it's easier to
just regex those away. The important details are all still asserted as I
understand things.
Fixes#119193.
@rustbot label: +llvm-main
Rollup of 5 pull requests
Successful merges:
- #118729 (Add release notes for 1.75.0)
- #119124 (don't build `rust-analyzer-proc-macro-srv` on def config )
- #119154 (Simple modification of `non_lifetime_binders`'s diagnostic information to adapt to type binders)
- #119176 (Fix name error in aarch64_apple_watchos tier 3 target)
- #119182 (Update sysinfo version to 0.30.0)
r? `@ghost`
`@rustbot` modify labels: rollup
Fix name error in aarch64_apple_watchos tier 3 target
fix llvm_target wrong name `aarch-apple-watchos` to `aarch64-apple-watchos`, sorry for my mistake.
previous pr: https://github.com/rust-lang/rust/pull/119074
r? compiler-team
Simple modification of `non_lifetime_binders`'s diagnostic information to adapt to type binders
fixes#119067
Replace diagnostic information "lifetime bounds cannot be used in this context" to "bounds cannot be used in this context".
```rust
#![allow(incomplete_features)]
#![feature(non_lifetime_binders)]
trait Trait {}
trait Trait2
where for <T: Trait> ():{}
//~^ ERROR bounds cannot be used in this context
```
Give `VariantData::Struct` named fields, to clairfy `recovered`.
Implements https://github.com/rust-lang/rust/pull/119121#discussion_r1431467066. Supersedes #119121
This way, it's clear what the bool fields means, instead of having to find where it's generated. Changes both ast and hir.
r? `@compiler-errors`
Add method to get instance instantiation arguments
Add a method to get the instance instantiation arguments, and include that information in the instance debug.
Fix crash due to `CrateItem::kind()` not handling constructors
Also add a method to get the instance instantiation arguments, and include that information in the instance debug.
do not allow ABI mismatches inside repr(C) types
In https://github.com/rust-lang/rust/pull/115476 we allowed ABI mismatches inside `repr(C)` types. This wasn't really discussed much; I added it because from how I understand calling conventions, this should actually be safe in practice. However I entirely forgot to actually allow this in Miri, and in the mean time I have learned that too much ABI compatibility can be a problem for CFI (it can reject fewer calls so that gives an attacker more room to play with).
So I propose we take back that part about ABI compatibility in `repr(C)`. It is anyway something that C and C++ do not allow, as far as I understand.
In the future we might want to introduce a class of ABI compatibilities where we say "this is a bug and it may lead to aborting the process, but it won't lead to arbitrary misbehavior -- worst case it'll just transmute the arguments from the caller type to the callee type". That would give CFI leeway to reject such calls without introducing the risk of arbitrary UB. (The UB can still happen if the transmute leads to bad results, of course, but it wouldn't be due to ABI weirdness.)
#115476 hasn't reached beta yet so if we land this before Dec 22nd we can just pretend this all never happened. ;) Otherwise we should do a beta backport (of the docs change at least).
Cc `@rust-lang/opsem` `@rust-lang/types`
coverage: Check for `async fn` explicitly, without needing a heuristic
The old code used a heuristic to detect async functions and adjust their coverage spans to produce better output. But there's no need to resort to a heuristic when we can just look back at the original definition and check whether the current function is actually an `async fn`.
In addition to being generally nicer, this also gets rid of the one piece of code that specifically cares about `CoverageSpan::is_closure` representing an actual closure. All remaining code that inspects that field just uses it as an indication that the span is a hole that should be carved out of other spans, and then discarded.
That opens up the possibility of introducing other kinds of “hole” spans, e.g. for nested functions/types/macros, and having them all behave uniformly.
---
`@rustbot` label +A-code-coverage
