diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs | 59 |
1 files changed, 54 insertions, 5 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs index 62933bce76b..7a930937255 100644 --- a/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs +++ b/compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs @@ -416,9 +416,59 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> { ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_predicate)) => { let trait_predicate = bound_predicate.rebind(trait_predicate); let trait_predicate = self.resolve_vars_if_possible(trait_predicate); - let trait_ref = trait_predicate.to_poly_trait_ref(); - if let Some(guar) = self.emit_specialized_closure_kind_error(&obligation, trait_ref) { + // Let's use the root obligation as the main message, when we care about the + // most general case ("X doesn't implement Pattern<'_>") over the case that + // happened to fail ("char doesn't implement Fn(&mut char)"). + // + // We rely on a few heuristics to identify cases where this root + // obligation is more important than the leaf obligation: + let (main_trait_predicate, o) = if let ty::PredicateKind::Clause( + ty::ClauseKind::Trait(root_pred) + ) = root_obligation.predicate.kind().skip_binder() + && !trait_predicate.self_ty().skip_binder().has_escaping_bound_vars() + && !root_pred.self_ty().has_escaping_bound_vars() + // The type of the leaf predicate is (roughly) the same as the type + // from the root predicate, as a proxy for "we care about the root" + // FIXME: this doesn't account for trivial derefs, but works as a first + // approximation. + && ( + // `T: Trait` && `&&T: OtherTrait`, we want `OtherTrait` + self.can_eq( + obligation.param_env, + trait_predicate.self_ty().skip_binder(), + root_pred.self_ty().peel_refs(), + ) + // `&str: Iterator` && `&str: IntoIterator`, we want `IntoIterator` + || self.can_eq( + obligation.param_env, + trait_predicate.self_ty().skip_binder(), + root_pred.self_ty(), + ) + ) + // The leaf trait and the root trait are different, so as to avoid + // talking about `&mut T: Trait` and instead remain talking about + // `T: Trait` instead + && trait_predicate.def_id() != root_pred.def_id() + // The root trait is not `Unsize`, as to avoid talking about it in + // `tests/ui/coercion/coerce-issue-49593-box-never.rs`. + && Some(root_pred.def_id()) != self.tcx.lang_items().unsize_trait() + { + ( + self.resolve_vars_if_possible( + root_obligation.predicate.kind().rebind(root_pred), + ), + root_obligation, + ) + } else { + (trait_predicate, &obligation) + }; + let trait_ref = main_trait_predicate.to_poly_trait_ref(); + + if let Some(guar) = self.emit_specialized_closure_kind_error( + &obligation, + trait_ref, + ) { return guar; } @@ -459,8 +509,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> { notes, parent_label, append_const_msg, - } = self.on_unimplemented_note(trait_ref, &obligation, &mut long_ty_file); - + } = self.on_unimplemented_note(trait_ref, o, &mut long_ty_file); let have_alt_message = message.is_some() || label.is_some(); let is_try_conversion = self.is_try_conversion(span, trait_ref.def_id()); let is_unsize = @@ -483,7 +532,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> { }; let err_msg = self.get_standard_error_message( - &trait_predicate, + &main_trait_predicate, message, predicate_is_const, append_const_msg, |