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Auto merge of #113201 - oli-obk:recursive_type_alias, r=estebank,compiler-errors

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Permit recursive weak type aliases

I saw #63097 and thought "we can do ~~better~~ funnier". So here it is. It's not useful, but it's certainly something. This may actually become feasible with lazy norm (so in 5 years (constant, not reducing over time)).

r? `@estebank`

cc `@GuillaumeGomez`
This commit is contained in:
bors 2023-09-01 07:10:21 +00:00
commit 96f62fce00
9 changed files with 104 additions and 22 deletions
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19
compiler/rustc_hir_analysis/src/astconv/mod.rs
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@ -910,19 +910,24 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
) -> Ty<'tcx> {
let tcx = self.tcx();
let args = self.ast_path_args_for_ty(span, did, item_segment);
let ty = tcx.at(span).type_of(did);
if let DefKind::TyAlias { lazy } = tcx.def_kind(did)
&& (lazy || ty.skip_binder().has_opaque_types())
{
// Type aliases referring to types that contain opaque types (but aren't just directly
// referencing a single opaque type) as well as those defined in crates that have the
if let DefKind::TyAlias { lazy: true } = tcx.def_kind(did) {
// Type aliases defined in crates that have the
// feature `lazy_type_alias` enabled get encoded as a type alias that normalization will
// then actually instantiate the where bounds of.
let alias_ty = tcx.mk_alias_ty(did, args);
Ty::new_alias(tcx, ty::Weak, alias_ty)
} else {
ty.instantiate(tcx, args)
let ty = tcx.at(span).type_of(did);
if ty.skip_binder().has_opaque_types() {
// Type aliases referring to types that contain opaque types (but aren't just directly
// referencing a single opaque type) get encoded as a type alias that normalization will
// then actually instantiate the where bounds of.
let alias_ty = tcx.mk_alias_ty(did, args);
Ty::new_alias(tcx, ty::Weak, alias_ty)
} else {
ty.instantiate(tcx, args)
}
}
}