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Auto merge of #118847 - eholk:for-await, r=compiler-errors
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`
2 parents 5085bf5 + 0315daa commit b29b02c

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5 files changed

+23
-13
lines changed

5 files changed

+23
-13
lines changed

‎src/closures.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -448,7 +448,7 @@ fn is_block_closure_forced(context: &RewriteContext<'_>, expr: &ast::Expr) -> bo
448448

449449
fn is_block_closure_forced_inner(expr: &ast::Expr, version: Version) -> bool {
450450
match expr.kind {
451-
ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop(..) => true,
451+
ast::ExprKind::If(..) | ast::ExprKind::While(..) | ast::ExprKind::ForLoop { .. } => true,
452452
ast::ExprKind::Loop(..) if version == Version::Two => true,
453453
ast::ExprKind::AddrOf(_, _, ref expr)
454454
| ast::ExprKind::Try(ref expr)
@@ -473,7 +473,7 @@ fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool {
473473
| ast::ExprKind::Block(..)
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| ast::ExprKind::While(..)
475475
| ast::ExprKind::Loop(..)
476-
| ast::ExprKind::ForLoop(..)
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| ast::ExprKind::ForLoop { .. }
477477
| ast::ExprKind::TryBlock(..) => false,
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_ => true,
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}

‎src/expr.rs

+17-7
Original file line numberDiff line numberDiff line change
@@ -3,7 +3,7 @@ use std::cmp::min;
33

44
use itertools::Itertools;
55
use rustc_ast::token::{Delimiter, Lit, LitKind};
6-
use rustc_ast::{ast, ptr, token};
6+
use rustc_ast::{ast, ptr, token, ForLoopKind};
77
use rustc_span::{BytePos, Span};
88

99
use crate::chains::rewrite_chain;
@@ -134,7 +134,7 @@ pub(crate) fn format_expr(
134134
}
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ast::ExprKind::Let(ref pat, ref expr, _span, _) => rewrite_let(context, shape, pat, expr),
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ast::ExprKind::If(..)
137-
| ast::ExprKind::ForLoop(..)
137+
| ast::ExprKind::ForLoop { .. }
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| ast::ExprKind::Loop(..)
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| ast::ExprKind::While(..) => to_control_flow(expr, expr_type)
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.and_then(|control_flow| control_flow.rewrite(context, shape)),
@@ -682,9 +682,15 @@ fn to_control_flow(expr: &ast::Expr, expr_type: ExprType) -> Option<ControlFlow<
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expr.span,
683683
))
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}
685-
ast::ExprKind::ForLoop(ref pat, ref cond, ref block, label) => {
686-
Some(ControlFlow::new_for(pat, cond, block, label, expr.span))
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}
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ast::ExprKind::ForLoop {
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ref pat,
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ref iter,
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ref body,
689+
label,
690+
kind,
691+
} => Some(ControlFlow::new_for(
692+
pat, iter, body, label, expr.span, kind,
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)),
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ast::ExprKind::Loop(ref block, label, _) => {
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Some(ControlFlow::new_loop(block, label, expr.span))
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}
@@ -771,14 +777,18 @@ impl<'a> ControlFlow<'a> {
771777
block: &'a ast::Block,
772778
label: Option<ast::Label>,
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span: Span,
780+
kind: ForLoopKind,
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) -> ControlFlow<'a> {
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ControlFlow {
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cond: Some(cond),
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block,
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else_block: None,
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label,
780787
pat: Some(pat),
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keyword: "for",
788+
keyword: match kind {
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ForLoopKind::For => "for",
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ForLoopKind::ForAwait => "for await",
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},
782792
matcher: "",
783793
connector: " in",
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allow_single_line: false,
@@ -1364,7 +1374,7 @@ pub(crate) fn can_be_overflowed_expr(
13641374
|| context.config.overflow_delimited_expr()
13651375
}
13661376
ast::ExprKind::If(..)
1367-
| ast::ExprKind::ForLoop(..)
1377+
| ast::ExprKind::ForLoop { .. }
13681378
| ast::ExprKind::Loop(..)
13691379
| ast::ExprKind::While(..) => {
13701380
context.config.combine_control_expr() && context.use_block_indent() && args_len == 1

‎src/matches.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -591,7 +591,7 @@ fn can_flatten_block_around_this(body: &ast::Expr) -> bool {
591591
ast::ExprKind::If(..) => false,
592592
// We do not allow collapsing a block around expression with condition
593593
// to avoid it being cluttered with match arm.
594-
ast::ExprKind::ForLoop(..) | ast::ExprKind::While(..) => false,
594+
ast::ExprKind::ForLoop { .. } | ast::ExprKind::While(..) => false,
595595
ast::ExprKind::Loop(..)
596596
| ast::ExprKind::Match(..)
597597
| ast::ExprKind::Block(..)

‎src/overflow.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -409,7 +409,7 @@ impl<'a> Context<'a> {
409409
// When overflowing the expressions which consists of a control flow
410410
// expression, avoid condition to use multi line.
411411
ast::ExprKind::If(..)
412-
| ast::ExprKind::ForLoop(..)
412+
| ast::ExprKind::ForLoop { .. }
413413
| ast::ExprKind::Loop(..)
414414
| ast::ExprKind::While(..)
415415
| ast::ExprKind::Match(..) => {

‎src/utils.rs

+2-2
Original file line numberDiff line numberDiff line change
@@ -295,7 +295,7 @@ pub(crate) fn semicolon_for_stmt(
295295
) -> bool {
296296
match stmt.kind {
297297
ast::StmtKind::Semi(ref expr) => match expr.kind {
298-
ast::ExprKind::While(..) | ast::ExprKind::Loop(..) | ast::ExprKind::ForLoop(..) => {
298+
ast::ExprKind::While(..) | ast::ExprKind::Loop(..) | ast::ExprKind::ForLoop { .. } => {
299299
false
300300
}
301301
ast::ExprKind::Break(..) | ast::ExprKind::Continue(..) | ast::ExprKind::Ret(..) => {
@@ -476,7 +476,7 @@ pub(crate) fn is_block_expr(context: &RewriteContext<'_>, expr: &ast::Expr, repr
476476
| ast::ExprKind::ConstBlock(..)
477477
| ast::ExprKind::Gen(..)
478478
| ast::ExprKind::Loop(..)
479-
| ast::ExprKind::ForLoop(..)
479+
| ast::ExprKind::ForLoop { .. }
480480
| ast::ExprKind::TryBlock(..)
481481
| ast::ExprKind::Match(..) => repr.contains('\n'),
482482
ast::ExprKind::Paren(ref expr)

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