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Rollup merge of #110827 - compiler-errors:issue-110761-followup, r=cjgillot

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Fix lifetime suggestion for type aliases with objects in them

Fixes an issue identified in https://github.com/rust-lang/rust/issues/110761#issuecomment-1520678479

This suggestion, like many other borrowck suggestions, are very fragile and there are other ways to trigger strange behavior even after this PR, so this is just a small improvement and not a total rework 💀
This commit is contained in:
Dylan DPC 2023-05-08 11:39:20 +05:30 • committed by GitHub
commit e04c9019f0
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4 changed files with 72 additions and 6 deletions
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16
compiler/rustc_borrowck/src/diagnostics/region_errors.rs
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@ -845,7 +845,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
return;
}
let Some((alias_tys, alias_span)) = self
let Some((alias_tys, alias_span, lt_addition_span)) = self
.infcx
.tcx
.return_type_impl_or_dyn_traits_with_type_alias(suitable_region.def_id) else { return; };
@ -858,10 +858,20 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
()
}
if let TyKind::TraitObject(_, lt, _) = alias_ty.kind {
spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string()));
if lt.ident.name == kw::Empty {
spans_suggs.push((lt.ident.span.shrink_to_hi(), " + 'a".to_string()));
} else {
spans_suggs.push((lt.ident.span, "'a".to_string()));
}
}
}
spans_suggs.push((alias_span.shrink_to_hi(), "<'a>".to_string()));
if let Some(lt_addition_span) = lt_addition_span {
spans_suggs.push((lt_addition_span, "'a, ".to_string()));
} else {
spans_suggs.push((alias_span.shrink_to_hi(), "<'a>".to_string()));
}
diag.multipart_suggestion_verbose(
format!(
"to declare that the trait object {captures}, you can add a lifetime parameter `'a` in the type alias"