Auto merge of #107614 - compiler-errors:allow-elaborator-to-filter-only-super-traits, r=oli-obk

Split implied and super predicate queries, then allow elaborator to filter only supertraits

Split the `super_predicates_of` query into a new `implied_predicates_of` query. The former now only returns the *real* supertraits of a trait alias, and the latter now returns the implied predicates (which include all of the `where` clauses of the trait alias). The behavior of these queries is identical for regular traits.

Now that the two queries are split, we can add a new filter method to the elaborator, `filter_only_self()`, which can be used in instances that we need only the *supertrait* predicates, such as during the elaboration used in closure signature deduction. This toggles the usage of `super_predicates_of` instead of `implied_predicates_of` during elaboration of a trait predicate.

This supersedes #104745, and fixes the four independent bugs identified in that PR.
Fixes #104719
Fixes #106238
Fixes #110023
Fixes #109514

r? types

2 files changed, 5 insertions, 2 deletions

diff --git a/compiler/rustc_trait_selection/src/solve/assembly/mod.rs b/compiler/rustc_trait_selection/src/solve/assembly/mod.rs
index a33e8ef4b4a..7f0ceb6646c 100644
--- a/compiler/rustc_trait_selection/src/solve/assembly/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/assembly/mod.rs
@@ -505,7 +505,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         let tcx = self.tcx();
         let own_bounds: FxIndexSet<_> =
             bounds.iter().map(|bound| bound.with_self_ty(tcx, self_ty)).collect();
-        for assumption in elaborate(tcx, own_bounds.iter().copied()) {
+        for assumption in elaborate(tcx, own_bounds.iter().copied())
+            // we only care about bounds that match the `Self` type
+            .filter_only_self()
+        {
             // FIXME: Predicates are fully elaborated in the object type's existential bounds
             // list. We want to only consider these pre-elaborated projections, and not other
             // projection predicates that we reach by elaborating the principal trait ref,
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 00c9a352258..60630979b34 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -115,7 +115,7 @@ impl<'tcx> TraitAliasExpander<'tcx> {
         }
 
         // Get components of trait alias.
-        let predicates = tcx.super_predicates_of(trait_ref.def_id());
+        let predicates = tcx.implied_predicates_of(trait_ref.def_id());
         debug!(?predicates);
 
         let items = predicates.predicates.iter().rev().filter_map(|(pred, span)| {