Rollup merge of #119222 - eholk:into-async-iterator, r=compiler-errors,dtolnay
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
GitHub
commit
eef023c806
@ -1814,7 +1814,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
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arena_vec![self; head],
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)
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}
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ForLoopKind::ForAwait => self.arena.alloc(head),
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// ` unsafe { Pin::new_unchecked(&mut into_async_iter(<head>)) }`
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ForLoopKind::ForAwait => {
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// `::core::async_iter::IntoAsyncIterator::into_async_iter(<head>)`
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let iter = self.expr_call_lang_item_fn(
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head_span,
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hir::LangItem::IntoAsyncIterIntoIter,
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arena_vec![self; head],
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);
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let iter = self.expr_mut_addr_of(head_span, iter);
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// `Pin::new_unchecked(...)`
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let iter = self.arena.alloc(self.expr_call_lang_item_fn_mut(
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head_span,
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hir::LangItem::PinNewUnchecked,
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arena_vec![self; iter],
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));
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// `unsafe { ... }`
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let iter = self.arena.alloc(self.expr_unsafe(iter));
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iter
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}
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};
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let match_expr = self.arena.alloc(self.expr_match(
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@ -308,6 +308,7 @@ language_item_table! {
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FuturePoll, sym::poll, future_poll_fn, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
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AsyncIteratorPollNext, sym::async_iterator_poll_next, async_iterator_poll_next, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::Exact(0);
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IntoAsyncIterIntoIter, sym::into_async_iter_into_iter, into_async_iter_into_iter, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::Exact(0);
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Option, sym::Option, option_type, Target::Enum, GenericRequirement::None;
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OptionSome, sym::Some, option_some_variant, Target::Variant, GenericRequirement::None;
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@ -135,3 +135,26 @@ impl<T> Poll<Option<T>> {
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#[lang = "AsyncGenFinished"]
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pub const FINISHED: Self = Poll::Ready(None);
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}
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/// Convert something into an async iterator
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#[unstable(feature = "async_iterator", issue = "79024")]
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pub trait IntoAsyncIterator {
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/// The type of the item yielded by the iterator
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type Item;
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/// The type of the resulting iterator
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type IntoAsyncIter: AsyncIterator<Item = Self::Item>;
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/// Converts `self` into an async iterator
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#[cfg_attr(not(bootstrap), lang = "into_async_iter_into_iter")]
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fn into_async_iter(self) -> Self::IntoAsyncIter;
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}
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#[unstable(feature = "async_iterator", issue = "79024")]
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impl<I: AsyncIterator> IntoAsyncIterator for I {
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type Item = I::Item;
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type IntoAsyncIter = I;
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fn into_async_iter(self) -> Self::IntoAsyncIter {
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self
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}
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}
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@ -124,5 +124,5 @@
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mod async_iter;
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mod from_iter;
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pub use async_iter::AsyncIterator;
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pub use async_iter::{AsyncIterator, IntoAsyncIterator};
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pub use from_iter::{from_iter, FromIter};
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17
library/core/tests/async_iter/mod.rs
Normal file
17
library/core/tests/async_iter/mod.rs
Normal file
@ -0,0 +1,17 @@
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use core::async_iter::{self, AsyncIterator, IntoAsyncIterator};
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use core::pin::pin;
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use core::task::Poll;
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#[test]
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fn into_async_iter() {
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let async_iter = async_iter::from_iter(0..3);
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let mut async_iter = pin!(async_iter.into_async_iter());
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let waker = core::task::Waker::noop();
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let mut cx = &mut core::task::Context::from_waker(&waker);
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assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(Some(0)));
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assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(Some(1)));
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assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(Some(2)));
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assert_eq!(async_iter.as_mut().poll_next(&mut cx), Poll::Ready(None));
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}
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@ -4,6 +4,8 @@
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#![feature(array_windows)]
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#![feature(ascii_char)]
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#![feature(ascii_char_variants)]
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#![feature(async_iter_from_iter)]
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#![feature(async_iterator)]
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#![feature(bigint_helper_methods)]
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#![feature(cell_update)]
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#![feature(const_align_offset)]
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@ -55,6 +57,7 @@
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#![feature(maybe_uninit_write_slice)]
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#![feature(maybe_uninit_uninit_array_transpose)]
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#![feature(min_specialization)]
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#![feature(noop_waker)]
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#![feature(numfmt)]
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#![feature(num_midpoint)]
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#![feature(isqrt)]
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@ -125,6 +128,7 @@ mod any;
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mod array;
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mod ascii;
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mod asserting;
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mod async_iter;
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mod atomic;
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mod bool;
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mod cell;
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@ -33,7 +33,14 @@ error[E0223]: ambiguous associated type
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--> $DIR/issue-109071.rs:15:22
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LL | fn T() -> Option<Self::Item> {}
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| ^^^^^^^^^^ help: use fully-qualified syntax: `<Windows<T> as IntoIterator>::Item`
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| ^^^^^^^^^^
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help: use fully-qualified syntax
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LL | fn T() -> Option<<Windows<T> as IntoAsyncIterator>::Item> {}
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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LL | fn T() -> Option<<Windows<T> as IntoIterator>::Item> {}
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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error: aborting due to 4 previous errors
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@ -5,22 +5,17 @@ LL | let iter = core::async_iter::from_iter(0..3);
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| ---- move occurs because `iter` has type `FromIter<std::ops::Range<i32>>`, which does not implement the `Copy` trait
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LL | let mut count = 0;
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LL | for await i in iter {
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| -------------------
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| | |
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| | value moved here
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| inside of this loop
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| ---- `iter` moved due to this method call
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...
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LL | for await i in iter {
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| ^^^^ value used here after move
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help: consider cloning the value if the performance cost is acceptable
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note: `into_async_iter` takes ownership of the receiver `self`, which moves `iter`
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--> $SRC_DIR/core/src/async_iter/async_iter.rs:LL:COL
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help: you can `clone` the value and consume it, but this might not be your desired behavior
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LL | for await i in iter.clone() {
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| ++++++++
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help: borrow this binding in the pattern to avoid moving the value
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LL | for await i in ref iter {
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| +++
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error: aborting due to 1 previous error
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@ -2,7 +2,14 @@ error[E0223]: ambiguous associated type
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--> $DIR/suggest-trait-in-ufcs-in-hrtb.rs:5:38
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LL | impl<S> Foo for Bar<S> where for<'a> <&'a S>::Item: Foo {}
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| ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<&'a S as IntoIterator>::Item`
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| ^^^^^^^^^^^^^
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help: use fully-qualified syntax
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LL | impl<S> Foo for Bar<S> where for<'a> <&'a S as IntoAsyncIterator>::Item: Foo {}
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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LL | impl<S> Foo for Bar<S> where for<'a> <&'a S as IntoIterator>::Item: Foo {}
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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error: aborting due to 1 previous error
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@ -2,7 +2,14 @@ error[E0223]: ambiguous associated type
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--> $DIR/issue-110052.rs:6:30
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LL | for<'iter> dyn Validator<<&'iter I>::Item>:,
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| ^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<&'iter I as IntoIterator>::Item`
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| ^^^^^^^^^^^^^^^^
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help: use fully-qualified syntax
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LL | for<'iter> dyn Validator<<&'iter I as IntoAsyncIterator>::Item>:,
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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LL | for<'iter> dyn Validator<<&'iter I as IntoIterator>::Item>:,
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| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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error: aborting due to 1 previous error
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