From 38df5bdcf1fee2dc4a7a566afee0f0f161417701 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 11 Feb 2024 18:23:05 +0000
Subject: [PATCH] Ignore own item bounds in parent alias types in
`for_each_item_bound`
---
.../src/traits/select/mod.rs | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index ac6cfcdeb5950..fb2f1da325292 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -1605,6 +1605,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
on_ambiguity: impl FnOnce(),
) -> ControlFlow<T, ()> {
let mut idx = 0;
+ let mut in_parent_alias_type = false;
+
loop {
let (kind, alias_ty) = match *self_ty.kind() {
ty::Alias(kind @ (ty::Projection | ty::Opaque), alias_ty) => (kind, alias_ty),
@@ -1618,6 +1620,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
for bound in
self.tcx().item_bounds(alias_ty.def_id).instantiate(self.tcx(), alias_ty.args)
{
+ // HACK: On subsequent recursions, we only care about bounds that don't
+ // share the same type as `self_ty`. This is because for truly rigid
+ // projections, we will never be able to equate, e.g. `<T as Tr>::A`
+ // with `<<T as Tr>::A as Tr>::A`.
+ if in_parent_alias_type {
+ match bound.kind().skip_binder() {
+ ty::ClauseKind::Trait(tr) if tr.self_ty() == self_ty => continue,
+ ty::ClauseKind::Projection(p) if p.self_ty() == self_ty => continue,
+ _ => {}
+ }
+ }
+
for_each(self, bound, idx)?;
idx += 1;
}
@@ -1627,6 +1641,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
} else {
return ControlFlow::Continue(());
}
+
+ in_parent_alias_type = true;
}
}