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Rollup merge of #134951 - compiler-errors:double-trait-err-msg, r=davidtwco

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Suppress host effect predicates if underlying trait doesn't hold

Don't report two errors for when the (`HostEffectPredicate`) `T: const Trait` isn't implemented because (`TraitPredicate`) `T: Trait` doesn't even hold.
This commit is contained in:
Matthias Krüger 2025-01-06 20:59:33 +01:00 • committed by GitHub
commit 68791efa29
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GPG key ID: B5690EEEBB952194
3 changed files with 101 additions and 19 deletions
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57
compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs
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@ -114,7 +114,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
//
// 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(
let (main_trait_predicate, main_obligation) = if let ty::PredicateKind::Clause(
ty::ClauseKind::Trait(root_pred)
) = root_obligation.predicate.kind().skip_binder()
&& !leaf_trait_predicate.self_ty().skip_binder().has_escaping_bound_vars()
@ -199,7 +199,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
notes,
parent_label,
append_const_msg,
} = self.on_unimplemented_note(main_trait_predicate, o, &mut long_ty_file);
} = self.on_unimplemented_note(main_trait_predicate, main_obligation, &mut long_ty_file);
let have_alt_message = message.is_some() || label.is_some();
let is_try_conversion = self.is_try_conversion(span, main_trait_ref.def_id());
@ -538,23 +538,7 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
}
ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(predicate)) => {
// FIXME(const_trait_impl): We should recompute the predicate with `~const`
// if it's `const`, and if it holds, explain that this bound only
// *conditionally* holds. If that fails, we should also do selection
// to drill this down to an impl or built-in source, so we can
// point at it and explain that while the trait *is* implemented,
// that implementation is not const.
let err_msg = self.get_standard_error_message(
bound_predicate.rebind(ty::TraitPredicate {
trait_ref: predicate.trait_ref,
polarity: ty::PredicatePolarity::Positive,
}),
None,
Some(predicate.constness),
None,
String::new(),
);
struct_span_code_err!(self.dcx(), span, E0277, "{}", err_msg)
self.report_host_effect_error(bound_predicate.rebind(predicate), obligation.param_env, span)
}
ty::PredicateKind::Subtype(predicate) => {
@ -763,6 +747,41 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
applied_do_not_recommend
}
fn report_host_effect_error(
&self,
predicate: ty::Binder<'tcx, ty::HostEffectPredicate<'tcx>>,
param_env: ty::ParamEnv<'tcx>,
span: Span,
) -> Diag<'a> {
// FIXME(const_trait_impl): We should recompute the predicate with `~const`
// if it's `const`, and if it holds, explain that this bound only
// *conditionally* holds. If that fails, we should also do selection
// to drill this down to an impl or built-in source, so we can
// point at it and explain that while the trait *is* implemented,
// that implementation is not const.
let trait_ref = predicate.map_bound(|predicate| ty::TraitPredicate {
trait_ref: predicate.trait_ref,
polarity: ty::PredicatePolarity::Positive,
});
let err_msg = self.get_standard_error_message(
trait_ref,
None,
Some(predicate.constness()),
None,
String::new(),
);
let mut diag = struct_span_code_err!(self.dcx(), span, E0277, "{}", err_msg);
if !self.predicate_may_hold(&Obligation::new(
self.tcx,
ObligationCause::dummy(),
param_env,
trait_ref,
)) {
diag.downgrade_to_delayed_bug();
}
diag
}
fn emit_specialized_closure_kind_error(
&self,
obligation: &PredicateObligation<'tcx>,