diff --git a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs index 4004fdd073ce..c92dfa24f85e 100644 --- a/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs +++ b/compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs @@ -966,6 +966,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { }; let self_ty = trait_pred.skip_binder().self_ty(); let found_ty = trait_pred.skip_binder().trait_ref.args.get(1).and_then(|a| a.as_type()); + self.note_missing_impl_for_question_mark(err, self_ty, found_ty, trait_pred); let mut prev_ty = self.resolve_vars_if_possible( typeck.expr_ty_adjusted_opt(expr).unwrap_or(Ty::new_misc_error(self.tcx)), @@ -1130,6 +1131,56 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> { suggested } + fn note_missing_impl_for_question_mark( + &self, + err: &mut Diag<'_>, + self_ty: Ty<'_>, + found_ty: Option>, + trait_pred: ty::PolyTraitPredicate<'tcx>, + ) { + match (self_ty.kind(), found_ty) { + (ty::Adt(def, _), Some(ty)) + if let ty::Adt(found, _) = ty.kind() + && def.did().is_local() + && found.did().is_local() => + { + err.span_note( + self.tcx.def_span(def.did()), + format!("`{self_ty}` needs to implement `From<{ty}>`"), + ); + err.span_note( + self.tcx.def_span(found.did()), + format!("alternatively, `{ty}` needs to implement `Into<{self_ty}>`"), + ); + } + (ty::Adt(def, _), None) if def.did().is_local() => { + err.span_note( + self.tcx.def_span(def.did()), + format!( + "`{self_ty}` needs to implement `{}`", + trait_pred.skip_binder().trait_ref.print_only_trait_path(), + ), + ); + } + (ty::Adt(def, _), Some(ty)) if def.did().is_local() => { + err.span_note( + self.tcx.def_span(def.did()), + format!("`{self_ty}` needs to implement `From<{ty}>`"), + ); + } + (_, Some(ty)) + if let ty::Adt(def, _) = ty.kind() + && def.did().is_local() => + { + err.span_note( + self.tcx.def_span(def.did()), + format!("`{ty}` needs to implement `Into<{self_ty}>`"), + ); + } + _ => {} + } + } + fn report_const_param_not_wf( &self, ty: Ty<'tcx>, diff --git a/tests/ui/try-trait/bad-question-mark-on-trait-object.rs b/tests/ui/try-trait/bad-question-mark-on-trait-object.rs index 9efac78b3d78..2a0d14b17503 100644 --- a/tests/ui/try-trait/bad-question-mark-on-trait-object.rs +++ b/tests/ui/try-trait/bad-question-mark-on-trait-object.rs @@ -1,5 +1,7 @@ struct E; -struct X; +//~^ NOTE `E` needs to implement `std::error::Error` +//~| NOTE alternatively, `E` needs to implement `Into` +struct X; //~ NOTE `X` needs to implement `From` fn foo() -> Result<(), Box> { //~ NOTE required `E: std::error::Error` because of this Ok(bar()?) diff --git a/tests/ui/try-trait/bad-question-mark-on-trait-object.stderr b/tests/ui/try-trait/bad-question-mark-on-trait-object.stderr index adebc16915d7..dd380850c9ec 100644 --- a/tests/ui/try-trait/bad-question-mark-on-trait-object.stderr +++ b/tests/ui/try-trait/bad-question-mark-on-trait-object.stderr @@ -1,5 +1,5 @@ error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied - --> $DIR/bad-question-mark-on-trait-object.rs:5:13 + --> $DIR/bad-question-mark-on-trait-object.rs:7:13 | LL | fn foo() -> Result<(), Box> { | -------------------------------------- required `E: std::error::Error` because of this @@ -8,11 +8,16 @@ LL | Ok(bar()?) | | | this has type `Result<_, E>` | +note: `E` needs to implement `std::error::Error` + --> $DIR/bad-question-mark-on-trait-object.rs:1:1 + | +LL | struct E; + | ^^^^^^^^ = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = note: required for `Box` to implement `From` error[E0277]: `?` couldn't convert the error to `X` - --> $DIR/bad-question-mark-on-trait-object.rs:16:13 + --> $DIR/bad-question-mark-on-trait-object.rs:18:13 | LL | fn bat() -> Result<(), X> { | ------------- expected `X` because of this @@ -21,6 +26,16 @@ LL | Ok(bar()?) | | | this can't be annotated with `?` because it has type `Result<_, E>` | +note: `X` needs to implement `From` + --> $DIR/bad-question-mark-on-trait-object.rs:4:1 + | +LL | struct X; + | ^^^^^^^^ +note: alternatively, `E` needs to implement `Into` + --> $DIR/bad-question-mark-on-trait-object.rs:1:1 + | +LL | struct E; + | ^^^^^^^^ = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait error: aborting due to 2 previous errors