Assert that explicit_super_predicates_of and explicit_item_bounds truly only bounds for the type itself

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -10,6 +10,7 @@
 use rustc_type_ir::Upcast;
 use tracing::{debug, instrument};
 
+use super::predicates_of::assert_only_contains_predicates_from;
 use super::ItemCtxt;
 use crate::hir_ty_lowering::{HirTyLowerer, PredicateFilter};
 
@@ -56,6 +57,9 @@ fn associated_type_bounds<'tcx>(
         tcx.def_path_str(assoc_item_def_id.to_def_id()),
         all_bounds
     );
+
+    assert_only_contains_predicates_from(filter, all_bounds, item_ty);
+
     all_bounds
 }
 
@@ -108,18 +112,21 @@ pub(super) fn explicit_item_bounds_with_filter(
         Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
             let item = tcx.hir_node_by_def_id(opaque_def_id.expect_local()).expect_item();
             let opaque_ty = item.expect_opaque_ty();
-            return ty::EarlyBinder::bind(opaque_type_bounds(
+            let item_ty = Ty::new_projection_from_args(
-                tcx,
-                opaque_def_id.expect_local(),
-                opaque_ty.bounds,
-                Ty::new_projection_from_args(
                 tcx,
                 def_id.to_def_id(),
                 ty::GenericArgs::identity_for_item(tcx, def_id),
-                ),
+            );
+            let bounds = opaque_type_bounds(
+                tcx,
+                opaque_def_id.expect_local(),
+                opaque_ty.bounds,
+                item_ty,
                 item.span,
                 filter,
-            ));
+            );
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            return ty::EarlyBinder::bind(bounds);
         }
         Some(ty::ImplTraitInTraitData::Impl { .. }) => span_bug!(
             tcx.def_span(def_id),
@@ -167,7 +174,9 @@ pub(super) fn explicit_item_bounds_with_filter(
         }) => {
             let args = GenericArgs::identity_for_item(tcx, def_id);
             let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
+            let bounds = opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter);
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            bounds
         }
         // Since RPITITs are lowered as projections in `<dyn HirTyLowerer>::lower_ty`, when we're
         // asking for the item bounds of the *opaques* in a trait's default method signature, we
@@ -184,15 +193,18 @@ pub(super) fn explicit_item_bounds_with_filter(
             };
             let args = GenericArgs::identity_for_item(tcx, def_id);
             let item_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);
-            tcx.arena.alloc_slice(
+            let bounds = &*tcx.arena.alloc_slice(
                 &opaque_type_bounds(tcx, def_id, bounds, item_ty, *span, filter)
                     .to_vec()
                     .fold_with(&mut AssocTyToOpaque { tcx, fn_def_id: fn_def_id.to_def_id() }),
-            )
+            );
+            assert_only_contains_predicates_from(filter, bounds, item_ty);
+            bounds
         }
         hir::Node::Item(hir::Item { kind: hir::ItemKind::TyAlias(..), .. }) => &[],
         _ => bug!("item_bounds called on {:?}", def_id),
     };
+
     ty::EarlyBinder::bind(bounds)
 }
 

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -676,9 +676,63 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
         _ => {}
     }
 
+    assert_only_contains_predicates_from(filter, implied_bounds, tcx.types.self_param);
+
     ty::EarlyBinder::bind(implied_bounds)
 }
 
+// Make sure when elaborating supertraits, probing for associated types, etc.,
+// we really truly are elaborating clauses that have `Self` as their self type.
+// This is very important since downstream code relies on this being correct.
+pub(super) fn assert_only_contains_predicates_from<'tcx>(
+    filter: PredicateFilter,
+    bounds: &'tcx [(ty::Clause<'tcx>, Span)],
+    ty: Ty<'tcx>,
+) {
+    if !cfg!(debug_assertions) {
+        return;
+    }
+
+    match filter {
+        PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => {
+            for (clause, _) in bounds {
+                match clause.kind().skip_binder() {
+                    ty::ClauseKind::Trait(trait_predicate) => {
+                        assert_eq!(
+                            trait_predicate.self_ty(),
+                            ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                    ty::ClauseKind::Projection(projection_predicate) => {
+                        assert_eq!(
+                            projection_predicate.self_ty(),
+                            ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                    ty::ClauseKind::TypeOutlives(outlives_predicate) => {
+                        assert_eq!(
+                            outlives_predicate.0, ty,
+                            "expected `Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+
+                    ty::ClauseKind::RegionOutlives(_)
+                    | ty::ClauseKind::ConstArgHasType(_, _)
+                    | ty::ClauseKind::WellFormed(_)
+                    | ty::ClauseKind::ConstEvaluatable(_) => {
+                        bug!(
+                            "unexpected non-`Self` predicate when computing `{filter:?}` implied bounds: {clause:?}"
+                        );
+                    }
+                }
+            }
+        }
+        PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {}
+    }
+}
+
 /// Returns the predicates defined on `item_def_id` of the form
 /// `X: Foo` where `X` is the type parameter `def_id`.
 #[instrument(level = "trace", skip(tcx))]