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chenyukangchenyukang
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Suggest async block instead of async closure when possible
1 parent 1d113d2 commit 448097d

6 files changed

Lines changed: 121 additions & 7 deletions

‎compiler/rustc_trait_selection/src/error_reporting/traits/suggestions.rs‎

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@@ -798,6 +798,34 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
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return false;
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}
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// If this is a zero-argument async closure directly passed as an argument
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// and the expected type is `Future`, suggest using `async {}` block instead
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// of `async || {}`.
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if let ty::CoroutineClosure(def_id, args) = *self_ty.kind()
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&& let sig = args.as_coroutine_closure().coroutine_closure_sig().skip_binder()
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&& let ty::Tuple(inputs) = *sig.tupled_inputs_ty.kind()
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&& inputs.is_empty()
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&& self.tcx.is_lang_item(trait_pred.def_id(), LangItem::Future)
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&& let Some(hir::Node::Expr(hir::Expr {
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kind:
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hir::ExprKind::Closure(hir::Closure {
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kind: hir::ClosureKind::CoroutineClosure(CoroutineDesugaring::Async),
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fn_arg_span: Some(arg_span),
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..
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}),
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..
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})) = self.tcx.hir_get_if_local(def_id)
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&& obligation.cause.span.contains(*arg_span)
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{
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err.span_suggestion_verbose(
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arg_span.with_hi(arg_span.hi() + rustc_span::BytePos(1)),
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"use `async {}` instead of `async || {}` to introduce an async block",
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"",
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Applicability::MachineApplicable,
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);
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return true;
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}
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// Get the name of the callable and the arguments to be used in the suggestion.
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let msg = match def_id_or_name {
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DefIdOrName::DefId(def_id) => match self.tcx.def_kind(def_id) {

‎tests/ui/async-await/async-closures/suggest-async-block-issue-140265.rs‎

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@@ -0,0 +1,20 @@
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//@ edition:2024
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// Test that we suggest using `async {}` block instead of `async || {}` closure if possible
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use std::future::Future;
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fn takes_future(_fut: impl Future<Output = ()>) {}
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fn main() {
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// Basic case: suggest using async block
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takes_future(async || {
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//~^ ERROR is not a future
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println!("hi!");
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});
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// With arguments: should suggest calling the closure, not using async block
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takes_future(async |x: i32| {
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//~^ ERROR is not a future
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println!("{x}");
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});
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}

‎tests/ui/async-await/async-closures/suggest-async-block-issue-140265.stderr‎

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error[E0277]: `{async closure@$DIR/suggest-async-block-issue-140265.rs:10:18: 10:26}` is not a future
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--> $DIR/suggest-async-block-issue-140265.rs:10:18
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|
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LL | takes_future(async || {
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| _____------------_^
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| | |
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| | required by a bound introduced by this call
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LL | |
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LL | | println!("hi!");
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LL | | });
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| |_____^ `{async closure@$DIR/suggest-async-block-issue-140265.rs:10:18: 10:26}` is not a future
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|
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= help: the trait `Future` is not implemented for `{async closure@$DIR/suggest-async-block-issue-140265.rs:10:18: 10:26}`
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note: required by a bound in `takes_future`
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--> $DIR/suggest-async-block-issue-140265.rs:6:28
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|
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LL | fn takes_future(_fut: impl Future<Output = ()>) {}
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| ^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_future`
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help: use `async {}` instead of `async || {}` to introduce an async block
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|
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LL - takes_future(async || {
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LL + takes_future(async {
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|
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error[E0277]: `{async closure@$DIR/suggest-async-block-issue-140265.rs:16:18: 16:32}` is not a future
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--> $DIR/suggest-async-block-issue-140265.rs:16:18
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|
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LL | takes_future(async |x: i32| {
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| _____------------_^
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| | |
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| | required by a bound introduced by this call
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LL | |
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LL | | println!("{x}");
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LL | | });
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| |_____^ `{async closure@$DIR/suggest-async-block-issue-140265.rs:16:18: 16:32}` is not a future
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|
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= help: the trait `Future` is not implemented for `{async closure@$DIR/suggest-async-block-issue-140265.rs:16:18: 16:32}`
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note: required by a bound in `takes_future`
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--> $DIR/suggest-async-block-issue-140265.rs:6:28
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|
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LL | fn takes_future(_fut: impl Future<Output = ()>) {}
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| ^^^^^^^^^^^^^^^^^^^ required by this bound in `takes_future`
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help: use parentheses to call this closure
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|
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LL | }(/* i32 */));
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| +++++++++++
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0277`.

‎tests/ui/suggestions/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.fixed‎

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//@ edition:2018
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//@ run-rustfix
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#![allow(unused_variables)]
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use std::future::Future;
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async fn foo() {}
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fn bar(f: impl Future<Output=()>) {}
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fn main() {
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bar(foo()); //~ERROR E0277
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let async_closure = async || ();
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bar(async_closure()); //~ERROR E0277
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}

‎tests/ui/suggestions/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs‎

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//@ edition:2018
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//@ run-rustfix
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#![allow(unused_variables)]
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use std::future::Future;
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async fn foo() {}

‎tests/ui/suggestions/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.stderr‎

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@@ -1,5 +1,5 @@
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error[E0277]: `fn() -> impl Future<Output = ()> {foo}` is not a future
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:9:9
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:9
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|
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LL | bar(foo);
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| --- ^^^ `fn() -> impl Future<Output = ()> {foo}` is not a future
@@ -8,7 +8,7 @@ LL | bar(foo);
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|
99
= help: the trait `Future` is not implemented for fn item `fn() -> impl Future<Output = ()> {foo}`
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note: required by a bound in `bar`
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:6:16
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:8:16
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|
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LL | fn bar(f: impl Future<Output=()>) {}
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| ^^^^^^^^^^^^^^^^^ required by this bound in `bar`
@@ -17,17 +17,17 @@ help: use parentheses to call this function
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LL | bar(foo());
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| ++
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error[E0277]: `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:10:25: 10:33}` is not a future
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:11:9
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error[E0277]: `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:12:25: 12:33}` is not a future
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:13:9
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|
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LL | bar(async_closure);
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| --- ^^^^^^^^^^^^^ `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:10:25: 10:33}` is not a future
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| --- ^^^^^^^^^^^^^ `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:12:25: 12:33}` is not a future
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| |
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| required by a bound introduced by this call
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|
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= help: the trait `Future` is not implemented for `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:10:25: 10:33}`
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= help: the trait `Future` is not implemented for `{async closure@$DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:12:25: 12:33}`
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note: required by a bound in `bar`
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:6:16
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--> $DIR/async-fn-ctor-passed-as-arg-where-it-should-have-been-called.rs:8:16
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|
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LL | fn bar(f: impl Future<Output=()>) {}
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| ^^^^^^^^^^^^^^^^^ required by this bound in `bar`

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