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Auto merge of #98637 - cjgillot:bare-trait-anon-lt, r=petrochenkov

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Create fresh lifetime parameters for bare fn trait too

The current code fails to account for the equivalence between `dyn FnMut(&mut u8)` and bare `FnMut(&mut u8)`, and treated them differently.

This PR introduces a special case for `Fn` traits, which are always fully resolved.

Fixes #98616
Fixes #98726
This will require a beta-backport, as beta contains that bug.

r? `@petrochenkov`
This commit is contained in:
bors 2022-07-11 17:09:37 +00:00
commit 38b72154de
4 changed files with 100 additions and 0 deletions
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27
compiler/rustc_ast_lowering/src/lib.rs
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@ -1159,6 +1159,33 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
param_mode: ParamMode,
itctx: ImplTraitContext,
) -> hir::Ty<'hir> {
// Check whether we should interpret this as a bare trait object.
// This check mirrors the one in late resolution. We only introduce this special case in
// the rare occurence we need to lower `Fresh` anonymous lifetimes.
// The other cases when a qpath should be opportunistically made a trait object are handled
// by `ty_path`.
if qself.is_none()
&& let Some(partial_res) = self.resolver.get_partial_res(t.id)
&& partial_res.unresolved_segments() == 0
&& let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = partial_res.base_res()
{
let (bounds, lifetime_bound) = self.with_dyn_type_scope(true, |this| {
let bound = this.lower_poly_trait_ref(
&PolyTraitRef {
bound_generic_params: vec![],
trait_ref: TraitRef { path: path.clone(), ref_id: t.id },
span: t.span
},
itctx,
);
let bounds = this.arena.alloc_from_iter([bound]);
let lifetime_bound = this.elided_dyn_bound(t.span);
(bounds, lifetime_bound)
});
let kind = hir::TyKind::TraitObject(bounds, lifetime_bound, TraitObjectSyntax::None);
return hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.next_id() };
}
let id = self.lower_node_id(t.id);
let qpath = self.lower_qpath(t.id, qself, path, param_mode, itctx);
self.ty_path(id, t.span, qpath)