diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs index 7d754cbafa3..d3e0d3b8b18 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs @@ -987,6 +987,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { } self.explain_hrtb_projection(&mut err, trait_predicate, obligation.param_env, &obligation.cause); + self.suggest_desugaring_async_fn_in_trait(&mut err, trait_ref); // Return early if the trait is Debug or Display and the invocation // originates within a standard library macro, because the output diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs index a08ebe5a9ea..17e0e4fcb48 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs @@ -414,6 +414,12 @@ pub trait TypeErrCtxtExt<'tcx> { param_env: ty::ParamEnv<'tcx>, cause: &ObligationCause<'tcx>, ); + + fn suggest_desugaring_async_fn_in_trait( + &self, + err: &mut Diagnostic, + trait_ref: ty::PolyTraitRef<'tcx>, + ); } fn predicate_constraint(generics: &hir::Generics<'_>, pred: ty::Predicate<'_>) -> (Span, String) { @@ -4100,6 +4106,136 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> { }); } } + + fn suggest_desugaring_async_fn_in_trait( + &self, + err: &mut Diagnostic, + trait_ref: ty::PolyTraitRef<'tcx>, + ) { + // Don't suggest if RTN is active -- we should prefer a where-clause bound instead. + if self.tcx.features().return_type_notation { + return; + } + + let trait_def_id = trait_ref.def_id(); + + // Only suggest specifying auto traits + if !self.tcx.trait_is_auto(trait_def_id) { + return; + } + + // Look for an RPITIT + let ty::Alias(ty::Projection, alias_ty) = trait_ref.self_ty().skip_binder().kind() else { + return; + }; + let Some(ty::ImplTraitInTraitData::Trait { fn_def_id, opaque_def_id }) = + self.tcx.opt_rpitit_info(alias_ty.def_id) + else { + return; + }; + + let auto_trait = self.tcx.def_path_str(trait_def_id); + // ... which is a local function + let Some(fn_def_id) = fn_def_id.as_local() else { + // If it's not local, we can at least mention that the method is async, if it is. + if self.tcx.asyncness(fn_def_id).is_async() { + err.span_note( + self.tcx.def_span(fn_def_id), + format!( + "`{}::{}` is an `async fn` in trait, which does not \ + automatically imply that its future is `{auto_trait}`", + alias_ty.trait_ref(self.tcx), + self.tcx.item_name(fn_def_id) + ), + ); + } + return; + }; + let Some(hir::Node::TraitItem(item)) = self.tcx.hir().find_by_def_id(fn_def_id) else { + return; + }; + + // ... whose signature is `async` (i.e. this is an AFIT) + let (sig, body) = item.expect_fn(); + let hir::IsAsync::Async(async_span) = sig.header.asyncness else { + return; + }; + let Ok(async_span) = + self.tcx.sess.source_map().span_extend_while(async_span, |c| c.is_whitespace()) + else { + return; + }; + let hir::FnRetTy::Return(hir::Ty { kind: hir::TyKind::OpaqueDef(def, ..), .. }) = + sig.decl.output + else { + // This should never happen, but let's not ICE. + return; + }; + + // Check that this is *not* a nested `impl Future` RPIT in an async fn + // (i.e. `async fn foo() -> impl Future`) + if def.owner_id.to_def_id() != opaque_def_id { + return; + } + + let future = self.tcx.hir().item(*def).expect_opaque_ty(); + let Some(hir::GenericBound::LangItemTrait(_, _, _, generics)) = future.bounds.get(0) else { + // `async fn` should always lower to a lang item bound... but don't ICE. + return; + }; + let Some(hir::TypeBindingKind::Equality { term: hir::Term::Ty(future_output_ty) }) = + generics.bindings.get(0).map(|binding| binding.kind) + else { + // Also should never happen. + return; + }; + + let function_name = self.tcx.def_path_str(fn_def_id); + + let mut sugg = if future_output_ty.span.is_empty() { + vec![ + (async_span, String::new()), + ( + future_output_ty.span, + format!(" -> impl std::future::Future + {auto_trait}"), + ), + ] + } else { + vec![ + ( + future_output_ty.span.shrink_to_lo(), + "impl std::future::Future + {auto_trait}")), + (async_span, String::new()), + ] + }; + + // If there's a body, we also need to wrap it in `async {}` + if let hir::TraitFn::Provided(body) = body { + let body = self.tcx.hir().body(*body); + let body_span = body.value.span; + let body_span_without_braces = + body_span.with_lo(body_span.lo() + BytePos(1)).with_hi(body_span.hi() - BytePos(1)); + if body_span_without_braces.is_empty() { + sugg.push((body_span_without_braces, " async {} ".to_owned())); + } else { + sugg.extend([ + (body_span_without_braces.shrink_to_lo(), "async {".to_owned()), + (body_span_without_braces.shrink_to_hi(), "} ".to_owned()), + ]); + } + } + + err.multipart_suggestion( + format!( + "`{auto_trait}` can be made part of the associated future's \ + guarantees for all implementations of `{function_name}`" + ), + sugg, + Applicability::MachineApplicable, + ); + } } /// Add a hint to add a missing borrow or remove an unnecessary one. diff --git a/tests/ui/async-await/in-trait/auxiliary/foreign-async-fn.rs b/tests/ui/async-await/in-trait/auxiliary/foreign-async-fn.rs new file mode 100644 index 00000000000..bba886f175e --- /dev/null +++ b/tests/ui/async-await/in-trait/auxiliary/foreign-async-fn.rs @@ -0,0 +1,7 @@ +// edition:2021 + +#![feature(async_fn_in_trait)] + +pub trait Foo { + async fn test(); +} diff --git a/tests/ui/async-await/in-trait/missing-send-bound.stderr b/tests/ui/async-await/in-trait/missing-send-bound.stderr index 18185b75554..7e59d94d456 100644 --- a/tests/ui/async-await/in-trait/missing-send-bound.stderr +++ b/tests/ui/async-await/in-trait/missing-send-bound.stderr @@ -15,6 +15,11 @@ note: required by a bound in `assert_is_send` | LL | fn assert_is_send(_: impl Send) {} | ^^^^ required by this bound in `assert_is_send` +help: `Send` can be made part of the associated future's guarantees for all implementations of `Foo::bar` + | +LL - async fn bar(); +LL + fn bar() -> impl std::future::Future + Send; + | error: aborting due to previous error diff --git a/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.fixed b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.fixed new file mode 100644 index 00000000000..33c00587439 --- /dev/null +++ b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.fixed @@ -0,0 +1,20 @@ +// run-rustfix +// edition: 2021 + +#![feature(async_fn_in_trait, return_position_impl_trait_in_trait)] +#![allow(unused)] + +trait Foo { + fn test() -> impl std::future::Future + Send { async {} } + fn test2() -> impl std::future::Future + Send {async { 1 + 2 } } +} + +fn bar() { + fn needs_send(_: impl Send) {} + needs_send(T::test()); + //~^ ERROR `impl Future` cannot be sent between threads safely + needs_send(T::test2()); + //~^ ERROR `impl Future` cannot be sent between threads safely +} + +fn main() {} diff --git a/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.rs b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.rs new file mode 100644 index 00000000000..96b623d6988 --- /dev/null +++ b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.rs @@ -0,0 +1,20 @@ +// run-rustfix +// edition: 2021 + +#![feature(async_fn_in_trait, return_position_impl_trait_in_trait)] +#![allow(unused)] + +trait Foo { + async fn test() -> () {} + async fn test2() -> i32 { 1 + 2 } +} + +fn bar() { + fn needs_send(_: impl Send) {} + needs_send(T::test()); + //~^ ERROR `impl Future` cannot be sent between threads safely + needs_send(T::test2()); + //~^ ERROR `impl Future` cannot be sent between threads safely +} + +fn main() {} diff --git a/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.stderr b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.stderr new file mode 100644 index 00000000000..4319a14118b --- /dev/null +++ b/tests/ui/async-await/in-trait/send-on-async-fn-in-trait.stderr @@ -0,0 +1,43 @@ +error[E0277]: `impl Future` cannot be sent between threads safely + --> $DIR/send-on-async-fn-in-trait.rs:14:16 + | +LL | needs_send(T::test()); + | ---------- ^^^^^^^^^ `impl Future` cannot be sent between threads safely + | | + | required by a bound introduced by this call + | + = help: the trait `Send` is not implemented for `impl Future` +note: required by a bound in `needs_send` + --> $DIR/send-on-async-fn-in-trait.rs:13:27 + | +LL | fn needs_send(_: impl Send) {} + | ^^^^ required by this bound in `needs_send` +help: `Send` can be made part of the associated future's guarantees for all implementations of `Foo::test` + | +LL - async fn test() -> () {} +LL + fn test() -> impl std::future::Future + Send { async {} } + | + +error[E0277]: `impl Future` cannot be sent between threads safely + --> $DIR/send-on-async-fn-in-trait.rs:16:16 + | +LL | needs_send(T::test2()); + | ---------- ^^^^^^^^^^ `impl Future` cannot be sent between threads safely + | | + | required by a bound introduced by this call + | + = help: the trait `Send` is not implemented for `impl Future` +note: required by a bound in `needs_send` + --> $DIR/send-on-async-fn-in-trait.rs:13:27 + | +LL | fn needs_send(_: impl Send) {} + | ^^^^ required by this bound in `needs_send` +help: `Send` can be made part of the associated future's guarantees for all implementations of `Foo::test2` + | +LL - async fn test2() -> i32 { 1 + 2 } +LL + fn test2() -> impl std::future::Future + Send {async { 1 + 2 } } + | + +error: aborting due to 2 previous errors + +For more information about this error, try `rustc --explain E0277`. diff --git a/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.rs b/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.rs new file mode 100644 index 00000000000..83b69d72a96 --- /dev/null +++ b/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.rs @@ -0,0 +1,15 @@ +// aux-build:foreign-async-fn.rs +// edition:2021 + +#![feature(async_fn_in_trait)] + +extern crate foreign_async_fn; +use foreign_async_fn::Foo; + +fn bar() { + fn needs_send(_: impl Send) {} + needs_send(T::test()); + //~^ ERROR `impl Future` cannot be sent between threads safely +} + +fn main() {} diff --git a/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.stderr b/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.stderr new file mode 100644 index 00000000000..f337a04ba19 --- /dev/null +++ b/tests/ui/async-await/in-trait/send-on-foreign-async-fn-in-trait.stderr @@ -0,0 +1,23 @@ +error[E0277]: `impl Future` cannot be sent between threads safely + --> $DIR/send-on-foreign-async-fn-in-trait.rs:11:16 + | +LL | needs_send(T::test()); + | ---------- ^^^^^^^^^ `impl Future` cannot be sent between threads safely + | | + | required by a bound introduced by this call + | + = help: the trait `Send` is not implemented for `impl Future` +note: `::test` is an `async fn` in trait, which does not automatically imply that its future is `Send` + --> $DIR/auxiliary/foreign-async-fn.rs:6:5 + | +LL | async fn test(); + | ^^^^^^^^^^^^^^^^ +note: required by a bound in `needs_send` + --> $DIR/send-on-foreign-async-fn-in-trait.rs:10:27 + | +LL | fn needs_send(_: impl Send) {} + | ^^^^ required by this bound in `needs_send` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0277`.