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Account for sealed traits in trait bound errors

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When implementing a public trait with a private super-trait, we now emit
a note that the missing bound is not going to be able to be satisfied,
and we explain the concept of a sealed trait.
This commit is contained in:
Esteban Küber 2023-06-16 18:09:54 +00:00
parent 065a1f5df9
commit 717c481739
3 changed files with 61 additions and 0 deletions
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26
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
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@ -2724,6 +2724,32 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
let msg = format!("required by this bound in `{short_item_name}`");
multispan.push_span_label(span, msg);
err.span_note(multispan, descr);
if let ty::PredicateKind::Clause(clause) = predicate.kind().skip_binder()
&& let ty::ClauseKind::Trait(trait_pred) = clause
{
let def_id = trait_pred.def_id();
let visible_item = if let Some(local) = def_id.as_local() {
// Check for local traits being reachable.
let vis = &self.tcx.resolutions(()).effective_visibilities;
// Account for non-`pub` traits in the root of the local crate.
let is_locally_reachable = self.tcx.parent(def_id).is_crate_root();
vis.is_reachable(local) || is_locally_reachable
} else {
// Check for foreign traits being reachable.
self.tcx.visible_parent_map(()).get(&def_id).is_some()
};
if let DefKind::Trait = tcx.def_kind(item_def_id) && !visible_item {
// FIXME(estebank): extend this to search for all the types that do
// implement this trait and list them.
err.note(format!(
"`{short_item_name}` is a \"sealed trait\", because to implement \
it you also need to implelement `{}`, which is not accessible; \
this is usually done to force you to use one of the provided \
types that already implement it",
with_no_trimmed_paths!(tcx.def_path_str(def_id)),
));
}
}
} else {
err.span_note(tcx.def_span(item_def_id), descr);
}