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Add a note for ? on future in sync function
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@ -3594,52 +3594,64 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
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trait_pred: ty::PolyTraitPredicate<'tcx>,
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span: Span,
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) {
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if let Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)) =
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self.tcx.coroutine_kind(obligation.cause.body_id)
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let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
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let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
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let impls_future = self.type_implements_trait(
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future_trait,
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[self.tcx.instantiate_bound_regions_with_erased(self_ty)],
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obligation.param_env,
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);
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if !impls_future.must_apply_modulo_regions() {
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return;
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}
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let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
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// `<T as Future>::Output`
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let projection_ty = trait_pred.map_bound(|trait_pred| {
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Ty::new_projection(
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self.tcx,
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item_def_id,
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// Future::Output has no args
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[trait_pred.self_ty()],
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)
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});
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let InferOk { value: projection_ty, .. } =
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self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
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debug!(
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normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
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);
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let try_obligation = self.mk_trait_obligation_with_new_self_ty(
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obligation.param_env,
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trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())),
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);
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debug!(try_trait_obligation = ?try_obligation);
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if self.predicate_may_hold(&try_obligation)
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&& let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
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&& snippet.ends_with('?')
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{
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let future_trait = self.tcx.require_lang_item(LangItem::Future, None);
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let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
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let impls_future = self.type_implements_trait(
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future_trait,
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[self.tcx.instantiate_bound_regions_with_erased(self_ty)],
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obligation.param_env,
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);
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if !impls_future.must_apply_modulo_regions() {
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return;
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}
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let item_def_id = self.tcx.associated_item_def_ids(future_trait)[0];
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// `<T as Future>::Output`
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let projection_ty = trait_pred.map_bound(|trait_pred| {
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Ty::new_projection(
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self.tcx,
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item_def_id,
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// Future::Output has no args
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[trait_pred.self_ty()],
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)
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});
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let InferOk { value: projection_ty, .. } =
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self.at(&obligation.cause, obligation.param_env).normalize(projection_ty);
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debug!(
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normalized_projection_type = ?self.resolve_vars_if_possible(projection_ty)
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);
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let try_obligation = self.mk_trait_obligation_with_new_self_ty(
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obligation.param_env,
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trait_pred.map_bound(|trait_pred| (trait_pred, projection_ty.skip_binder())),
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);
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debug!(try_trait_obligation = ?try_obligation);
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if self.predicate_may_hold(&try_obligation)
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&& let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span)
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&& snippet.ends_with('?')
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{
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err.span_suggestion_verbose(
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span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(),
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"consider `await`ing on the `Future`",
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".await",
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Applicability::MaybeIncorrect,
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);
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match self.tcx.coroutine_kind(obligation.cause.body_id) {
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Some(hir::CoroutineKind::Desugared(hir::CoroutineDesugaring::Async, _)) => {
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err.span_suggestion_verbose(
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span.with_hi(span.hi() - BytePos(1)).shrink_to_hi(),
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"consider `await`ing on the `Future`",
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".await",
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Applicability::MaybeIncorrect,
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);
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}
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_ => {
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let mut span: MultiSpan = span.with_lo(span.hi() - BytePos(1)).into();
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span.push_span_label(
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self.tcx.def_span(obligation.cause.body_id),
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"this is not `async`",
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);
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err.span_note(
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span,
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"this implements `Future` and its output type supports \
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`?`, but the future cannot be awaited in a synchronous function",
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);
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}
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}
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}
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}
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9
tests/ui/async-await/try-in-sync.rs
Normal file
9
tests/ui/async-await/try-in-sync.rs
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@ -0,0 +1,9 @@
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//@ edition: 2021
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async fn foo() -> Result<(), ()> { todo!() }
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fn main() -> Result<(), ()> {
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foo()?;
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//~^ ERROR the `?` operator can only be applied to values that implement `Try`
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Ok(())
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}
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18
tests/ui/async-await/try-in-sync.stderr
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18
tests/ui/async-await/try-in-sync.stderr
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@ -0,0 +1,18 @@
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error[E0277]: the `?` operator can only be applied to values that implement `Try`
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--> $DIR/try-in-sync.rs:6:5
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LL | foo()?;
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| ^^^^^^ the `?` operator cannot be applied to type `impl Future<Output = Result<(), ()>>`
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= help: the trait `Try` is not implemented for `impl Future<Output = Result<(), ()>>`
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note: this implements `Future` and its output type supports `?`, but the future cannot be awaited in a synchronous function
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--> $DIR/try-in-sync.rs:6:10
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LL | fn main() -> Result<(), ()> {
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| --------------------------- this is not `async`
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LL | foo()?;
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| ^
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error: aborting due to 1 previous error
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For more information about this error, try `rustc --explain E0277`.
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