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Rollup merge of #119222 - eholk:into-async-iterator, r=compiler-errors,dtolnay

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Add `IntoAsyncIterator`

This introduces the `IntoAsyncIterator` trait and uses it in the desugaring of the unstable `for await` loop syntax. This is mostly added for symmetry with `Iterator` and `IntoIterator`.

r? `@compiler-errors`

cc `@rust-lang/libs-api,` `@rust-lang/wg-async`
This commit is contained in:
Michael Goulet 2023-12-22 21:41:04 -05:00 • committed by GitHub
commit eef023c806
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10 changed files with 93 additions and 14 deletions
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20
compiler/rustc_ast_lowering/src/expr.rs
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@ -1814,7 +1814,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
arena_vec![self; head],
)
}
ForLoopKind::ForAwait => self.arena.alloc(head),
// ` unsafe { Pin::new_unchecked(&mut into_async_iter(<head>)) }`
ForLoopKind::ForAwait => {
// `::core::async_iter::IntoAsyncIterator::into_async_iter(<head>)`
let iter = self.expr_call_lang_item_fn(
head_span,
hir::LangItem::IntoAsyncIterIntoIter,
arena_vec![self; head],
);
let iter = self.expr_mut_addr_of(head_span, iter);
// `Pin::new_unchecked(...)`
let iter = self.arena.alloc(self.expr_call_lang_item_fn_mut(
head_span,
hir::LangItem::PinNewUnchecked,
arena_vec![self; iter],
));
// `unsafe { ... }`
let iter = self.arena.alloc(self.expr_unsafe(iter));
iter
}
};
let match_expr = self.arena.alloc(self.expr_match(