Make sure type_param_predicates resolves correctly for RPITIT

Author: compiler-errors

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -764,6 +764,16 @@ pub(super) fn type_param_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
     (item_def_id, def_id, assoc_name): (LocalDefId, LocalDefId, Ident),
 ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
+    match tcx.opt_rpitit_info(item_def_id.to_def_id()) {
+        Some(ty::ImplTraitInTraitData::Trait { opaque_def_id, .. }) => {
+            return tcx.type_param_predicates((opaque_def_id.expect_local(), def_id, assoc_name));
+        }
+        Some(ty::ImplTraitInTraitData::Impl { .. }) => {
+            unreachable!("should not be lowering bounds on RPITIT in impl")
+        }
+        None => {}
+    }
+
     use rustc_hir::*;
     use rustc_middle::ty::Ty;
 

tests/ui/impl-trait/in-trait/shorthand-projection-in-rpitit-bound.rs

@@ -0,0 +1,13 @@
+//@ check-pass
+
+// Ensure that we can resolve a shorthand projection in an item bound in an RPITIT.
+
+pub trait Bar {
+    type Foo;
+}
+
+pub trait Baz {
+    fn boom<X: Bar>() -> impl Bar<Foo = X::Foo>;
+}
+
+fn main() {}