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Auto merge of #118420 - compiler-errors:async-gen, r=eholk

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Introduce support for `async gen` blocks

I'm delighted to demonstrate that `async gen` block are not very difficult to support. They're simply coroutines that yield `Poll<Option<T>>` and return `()`.

**This PR is WIP and in draft mode for now** -- I'm mostly putting it up to show folks that it's possible. This PR needs a lang-team experiment associated with it or possible an RFC, since I don't think it falls under the jurisdiction of the `gen` RFC that was recently authored by oli (https://github.com/rust-lang/rfcs/pull/3513, https://github.com/rust-lang/rust/issues/117078).

### Technical note on the pre-generator-transform yield type:

The reason that the underlying coroutines yield `Poll<Option<T>>` and not `Poll<T>` (which would make more sense, IMO, for the pre-transformed coroutine), is because the `TransformVisitor` that is used to turn coroutines into built-in state machine functions would have to destructure and reconstruct the latter into the former, which requires at least inserting a new basic block (for a `switchInt` terminator, to match on the `Poll` discriminant).

This does mean that the desugaring (at the `rustc_ast_lowering` level) of `async gen` blocks is a bit more involved. However, since we already need to intercept both `.await` and `yield` operators, I don't consider it much of a technical burden.

r? `@ghost`
This commit is contained in:
bors 2023-12-08 19:13:57 +00:00
commit f967532a47
61 changed files with 1120 additions and 357 deletions
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23
compiler/rustc_lint/src/early.rs
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@ -162,11 +162,10 @@ impl<'a, T: EarlyLintPass> ast_visit::Visitor<'a> for EarlyContextAndPass<'a, T>
// Explicitly check for lints associated with 'closure_id', since
// it does not have a corresponding AST node
if let ast_visit::FnKind::Fn(_, _, sig, _, _, _) = fk {
if let Some(
ast::CoroutineKind::Async { closure_id, .. }
| ast::CoroutineKind::Gen { closure_id, .. },
) = sig.header.coro_kind
{
if let Some(coro_kind) = sig.header.coroutine_kind {
let (ast::CoroutineKind::Async { closure_id, .. }
| ast::CoroutineKind::Gen { closure_id, .. }
| ast::CoroutineKind::AsyncGen { closure_id, .. }) = coro_kind;
self.check_id(closure_id);
}
}
@ -227,13 +226,13 @@ impl<'a, T: EarlyLintPass> ast_visit::Visitor<'a> for EarlyContextAndPass<'a, T>
// it does not have a corresponding AST node
match e.kind {
ast::ExprKind::Closure(box ast::Closure {
coro_kind:
Some(
ast::CoroutineKind::Async { closure_id, .. }
| ast::CoroutineKind::Gen { closure_id, .. },
),
..
}) => self.check_id(closure_id),
coroutine_kind: Some(coro_kind), ..
}) => {
let (ast::CoroutineKind::Async { closure_id, .. }
| ast::CoroutineKind::Gen { closure_id, .. }
| ast::CoroutineKind::AsyncGen { closure_id, .. }) = coro_kind;
self.check_id(closure_id);
}
_ => {}
}
lint_callback!(self, check_expr_post, e);