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tail expression behind terminating scope

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Ding Xiang Fei 2024-04-12 23:24:45 +08:00
parent 11380368dc
commit 0f8c3f7882
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GPG key ID: 3CD748647EEF6359
19 changed files with 377 additions and 24 deletions
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56
compiler/rustc_ast_lowering/src/expr.rs
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@ -1716,24 +1716,28 @@ impl<'hir> LoweringContext<'_, 'hir> {
// `mut iter => { ... }`
let iter_arm = self.arm(iter_pat, loop_expr);
let into_iter_expr = match loop_kind {
let match_expr = match loop_kind {
ForLoopKind::For => {
// `::std::iter::IntoIterator::into_iter(<head>)`
self.expr_call_lang_item_fn(
let into_iter_expr = self.expr_call_lang_item_fn(
head_span,
hir::LangItem::IntoIterIntoIter,
arena_vec![self; 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);
self.arena.alloc(self.expr_match(
for_span,
into_iter_expr,
arena_vec![self; iter_arm],
hir::MatchSource::ForLoopDesugar,
))
}
// `match into_async_iter(<head>) { ref mut iter => match unsafe { Pin::new_unchecked(iter) } { ... } }`
ForLoopKind::ForAwait => {
let iter_ident = iter;
let (async_iter_pat, async_iter_pat_id) =
self.pat_ident_binding_mode(head_span, iter_ident, hir::BindingMode::REF_MUT);
let iter = self.expr_ident_mut(head_span, iter_ident, async_iter_pat_id);
// `Pin::new_unchecked(...)`
let iter = self.arena.alloc(self.expr_call_lang_item_fn_mut(
head_span,
@ -1742,17 +1746,29 @@ impl<'hir> LoweringContext<'_, 'hir> {
));
// `unsafe { ... }`
let iter = self.arena.alloc(self.expr_unsafe(iter));
iter
let inner_match_expr = self.arena.alloc(self.expr_match(
for_span,
iter,
arena_vec![self; iter_arm],
hir::MatchSource::ForLoopDesugar,
));
// `::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_arm = self.arm(async_iter_pat, inner_match_expr);
self.arena.alloc(self.expr_match(
for_span,
iter,
arena_vec![self; iter_arm],
hir::MatchSource::ForLoopDesugar,
))
}
};
let match_expr = self.arena.alloc(self.expr_match(
for_span,
into_iter_expr,
arena_vec![self; iter_arm],
hir::MatchSource::ForLoopDesugar,
));
// This is effectively `{ let _result = ...; _result }`.
// The construct was introduced in #21984 and is necessary to make sure that
// temporaries in the `head` expression are dropped and do not leak to the