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Auto merge of #112686 - estebank:sealed-traits, r=petrochenkov

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Account for sealed traits in privacy and trait bound errors

On trait bound errors caused by super-traits, identify if the super-trait is publicly accessibly and if not, explain "sealed traits".

```
error[E0277]: the trait bound `S: Hidden` is not satisfied
  --> $DIR/sealed-trait-local.rs:17:20
   |
LL | impl a::Sealed for S {}
   |                    ^ the trait `Hidden` is not implemented for `S`
   |
note: required by a bound in `Sealed`
  --> $DIR/sealed-trait-local.rs:3:23
   |
LL |     pub trait Sealed: self:🅱️:Hidden {
   |                       ^^^^^^^^^^^^^^^ required by this bound in `Sealed`
   = note: `Sealed` is a "sealed trait", because to implement it you also need to implelement `a:🅱️:Hidden`, which is not accessible; this is usually done to force you to use one of the provided types that already implement it
```

Deduplicate privacy errors that point to the same path segment even if their deduplication span are different.

When encountering a path that is not reachable due to privacy constraints path segments other than the last, keep metadata for the last path segment's `Res` in order to look for alternative import paths for that item to suggest. If there are none, be explicit that the item is not accessible.

```
error[E0603]: module `b` is private
  --> $DIR/re-exported-trait.rs:11:9
   |
LL | impl a:🅱️:Trait for S {}
   |         ^ private module
   |
note: the module `b` is defined here
  --> $DIR/re-exported-trait.rs:5:5
   |
LL |     mod b {
   |     ^^^^^
help: consider importing this trait through its public re-export instead
   |
LL | impl a::Trait for S {}
   |      ~~~~~~~~
```

```
error[E0603]: module `b` is private
  --> $DIR/private-trait.rs:8:9
   |
LL | impl a:🅱️:Hidden for S {}
   |         ^  ------ trait `b` is not publicly reachable
   |         |
   |         private module
   |
note: the module `b` is defined here
  --> $DIR/private-trait.rs:2:5
   |
LL |     mod b {
   |     ^^^^^
```
This commit is contained in:
bors 2023-06-22 18:23:19 +00:00
commit 04075b3202
29 changed files with 337 additions and 54 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);
}