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Auto merge of #118420 - compiler-errors:async-gen, r=eholk
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 (rust-lang/rfcs#3513, #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`
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‎compiler/rustc_ast/src/ast.rs

+20-8
Original file line numberDiff line numberDiff line change
@@ -1329,7 +1329,7 @@ pub struct Closure {
13291329
pub binder: ClosureBinder,
13301330
pub capture_clause: CaptureBy,
13311331
pub constness: Const,
1332-
pub coro_kind: Option<CoroutineKind>,
1332+
pub coroutine_kind: Option<CoroutineKind>,
13331333
pub movability: Movability,
13341334
pub fn_decl: P<FnDecl>,
13351335
pub body: P<Expr>,
@@ -1534,6 +1534,7 @@ pub enum ExprKind {
15341534
pub enum GenBlockKind {
15351535
Async,
15361536
Gen,
1537+
AsyncGen,
15371538
}
15381539

15391540
impl fmt::Display for GenBlockKind {
@@ -1547,6 +1548,7 @@ impl GenBlockKind {
15471548
match self {
15481549
GenBlockKind::Async => "async",
15491550
GenBlockKind::Gen => "gen",
1551+
GenBlockKind::AsyncGen => "async gen",
15501552
}
15511553
}
15521554
}
@@ -2431,10 +2433,12 @@ pub enum Unsafe {
24312433
/// Iterator`.
24322434
#[derive(Copy, Clone, Encodable, Decodable, Debug)]
24332435
pub enum CoroutineKind {
2434-
/// `async`, which evaluates to `impl Future`
2436+
/// `async`, which returns an `impl Future`
24352437
Async { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
2436-
/// `gen`, which evaluates to `impl Iterator`
2438+
/// `gen`, which returns an `impl Iterator`
24372439
Gen { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
2440+
/// `async gen`, which returns an `impl AsyncIterator`
2441+
AsyncGen { span: Span, closure_id: NodeId, return_impl_trait_id: NodeId },
24382442
}
24392443

24402444
impl CoroutineKind {
@@ -2451,7 +2455,10 @@ impl CoroutineKind {
24512455
pub fn return_id(self) -> (NodeId, Span) {
24522456
match self {
24532457
CoroutineKind::Async { return_impl_trait_id, span, .. }
2454-
| CoroutineKind::Gen { return_impl_trait_id, span, .. } => (return_impl_trait_id, span),
2458+
| CoroutineKind::Gen { return_impl_trait_id, span, .. }
2459+
| CoroutineKind::AsyncGen { return_impl_trait_id, span, .. } => {
2460+
(return_impl_trait_id, span)
2461+
}
24552462
}
24562463
}
24572464
}
@@ -2856,7 +2863,7 @@ pub struct FnHeader {
28562863
/// The `unsafe` keyword, if any
28572864
pub unsafety: Unsafe,
28582865
/// Whether this is `async`, `gen`, or nothing.
2859-
pub coro_kind: Option<CoroutineKind>,
2866+
pub coroutine_kind: Option<CoroutineKind>,
28602867
/// The `const` keyword, if any
28612868
pub constness: Const,
28622869
/// The `extern` keyword and corresponding ABI string, if any
@@ -2866,17 +2873,22 @@ pub struct FnHeader {
28662873
impl FnHeader {
28672874
/// Does this function header have any qualifiers or is it empty?
28682875
pub fn has_qualifiers(&self) -> bool {
2869-
let Self { unsafety, coro_kind, constness, ext } = self;
2876+
let Self { unsafety, coroutine_kind, constness, ext } = self;
28702877
matches!(unsafety, Unsafe::Yes(_))
2871-
|| coro_kind.is_some()
2878+
|| coroutine_kind.is_some()
28722879
|| matches!(constness, Const::Yes(_))
28732880
|| !matches!(ext, Extern::None)
28742881
}
28752882
}
28762883

28772884
impl Default for FnHeader {
28782885
fn default() -> FnHeader {
2879-
FnHeader { unsafety: Unsafe::No, coro_kind: None, constness: Const::No, ext: Extern::None }
2886+
FnHeader {
2887+
unsafety: Unsafe::No,
2888+
coroutine_kind: None,
2889+
constness: Const::No,
2890+
ext: Extern::None,
2891+
}
28802892
}
28812893
}
28822894

‎compiler/rustc_ast/src/mut_visit.rs

+10-9
Original file line numberDiff line numberDiff line change
@@ -121,8 +121,8 @@ pub trait MutVisitor: Sized {
121121
noop_visit_fn_decl(d, self);
122122
}
123123

124-
fn visit_coro_kind(&mut self, a: &mut CoroutineKind) {
125-
noop_visit_coro_kind(a, self);
124+
fn visit_coroutine_kind(&mut self, a: &mut CoroutineKind) {
125+
noop_visit_coroutine_kind(a, self);
126126
}
127127

128128
fn visit_closure_binder(&mut self, b: &mut ClosureBinder) {
@@ -871,10 +871,11 @@ pub fn noop_visit_closure_binder<T: MutVisitor>(binder: &mut ClosureBinder, vis:
871871
}
872872
}
873873

874-
pub fn noop_visit_coro_kind<T: MutVisitor>(coro_kind: &mut CoroutineKind, vis: &mut T) {
875-
match coro_kind {
874+
pub fn noop_visit_coroutine_kind<T: MutVisitor>(coroutine_kind: &mut CoroutineKind, vis: &mut T) {
875+
match coroutine_kind {
876876
CoroutineKind::Async { span, closure_id, return_impl_trait_id }
877-
| CoroutineKind::Gen { span, closure_id, return_impl_trait_id } => {
877+
| CoroutineKind::Gen { span, closure_id, return_impl_trait_id }
878+
| CoroutineKind::AsyncGen { span, closure_id, return_impl_trait_id } => {
878879
vis.visit_span(span);
879880
vis.visit_id(closure_id);
880881
vis.visit_id(return_impl_trait_id);
@@ -1171,9 +1172,9 @@ fn visit_const_item<T: MutVisitor>(
11711172
}
11721173

11731174
pub fn noop_visit_fn_header<T: MutVisitor>(header: &mut FnHeader, vis: &mut T) {
1174-
let FnHeader { unsafety, coro_kind, constness, ext: _ } = header;
1175+
let FnHeader { unsafety, coroutine_kind, constness, ext: _ } = header;
11751176
visit_constness(constness, vis);
1176-
coro_kind.as_mut().map(|coro_kind| vis.visit_coro_kind(coro_kind));
1177+
coroutine_kind.as_mut().map(|coroutine_kind| vis.visit_coroutine_kind(coroutine_kind));
11771178
visit_unsafety(unsafety, vis);
11781179
}
11791180

@@ -1407,7 +1408,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
14071408
binder,
14081409
capture_clause,
14091410
constness,
1410-
coro_kind,
1411+
coroutine_kind,
14111412
movability: _,
14121413
fn_decl,
14131414
body,
@@ -1416,7 +1417,7 @@ pub fn noop_visit_expr<T: MutVisitor>(
14161417
}) => {
14171418
vis.visit_closure_binder(binder);
14181419
visit_constness(constness, vis);
1419-
coro_kind.as_mut().map(|coro_kind| vis.visit_coro_kind(coro_kind));
1420+
coroutine_kind.as_mut().map(|coroutine_kind| vis.visit_coroutine_kind(coroutine_kind));
14201421
vis.visit_capture_by(capture_clause);
14211422
vis.visit_fn_decl(fn_decl);
14221423
vis.visit_expr(body);

‎compiler/rustc_ast/src/visit.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -861,7 +861,7 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
861861
ExprKind::Closure(box Closure {
862862
binder,
863863
capture_clause,
864-
coro_kind: _,
864+
coroutine_kind: _,
865865
constness: _,
866866
movability: _,
867867
fn_decl,

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