Use IntoAsyncIterator in for await loop desugaring

eholk · eholk · commit acb6f17adf78 · 2023-12-22T11:01:06.000-08:00
diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
@@ -1803,7 +1803,25 @@ 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(
diff --git a/compiler/rustc_hir/src/lang_items.rs b/compiler/rustc_hir/src/lang_items.rs
@@ -308,6 +308,7 @@ language_item_table! {
     FuturePoll,              sym::poll,                future_poll_fn,             Target::Method(MethodKind::Trait { body: false }), GenericRequirement::None;
 
     AsyncIteratorPollNext,   sym::async_iterator_poll_next, async_iterator_poll_next, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::Exact(0);
+    IntoAsyncIterIntoIter,   sym::into_async_iter_into_iter, into_async_iter_into_iter, Target::Method(MethodKind::Trait { body: false }), GenericRequirement::Exact(0);
 
     Option,                  sym::Option,              option_type,                Target::Enum,           GenericRequirement::None;
     OptionSome,              sym::Some,                option_some_variant,        Target::Variant,        GenericRequirement::None;
diff --git a/library/core/src/async_iter/async_iter.rs b/library/core/src/async_iter/async_iter.rs
@@ -145,6 +145,7 @@ pub trait IntoAsyncIterator {
     type IntoAsyncIter: AsyncIterator<Item = Self::Item>;
 
     /// Converts `self` into an async iterator
+    #[cfg_attr(not(bootstrap), lang = "into_async_iter_into_iter")]
     fn into_async_iter(self) -> Self::IntoAsyncIter;
 }
 

Original file line number	Diff line number	Diff line change
`@@ -145,6 +145,7 @@ pub trait IntoAsyncIterator {`
`145`	`145`	`type IntoAsyncIter: AsyncIterator<Item = Self::Item>;`
`146`	`146`
`147`	`147`	/// Converts `self` into an async iterator
	`148`	`+ #[cfg_attr(not(bootstrap), lang = "into_async_iter_into_iter")]`
`148`	`149`	`fn into_async_iter(self) -> Self::IntoAsyncIter;`
`149`	`150`	`}`
`150`	`151`