Ensure valid TraitRefs are created for GATs

compiler/rustc_privacy/src/lib.rs

@@ -77,6 +77,12 @@ trait DefIdVisitor<'tcx> {
     fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> ControlFlow<Self::BreakTy> {
         self.skeleton().visit_trait(trait_ref)
     }
+    fn visit_projection_ty(
+        &mut self,
+        projection: ty::ProjectionTy<'tcx>,
+    ) -> ControlFlow<Self::BreakTy> {
+        self.skeleton().visit_projection_ty(projection)
+    }
     fn visit_predicates(
         &mut self,
         predicates: ty::GenericPredicates<'tcx>,
@@ -101,14 +107,28 @@ where
         if self.def_id_visitor.shallow() { ControlFlow::CONTINUE } else { substs.visit_with(self) }
     }
 
+    fn visit_projection_ty(
+        &mut self,
+        projection: ty::ProjectionTy<'tcx>,
+    ) -> ControlFlow<V::BreakTy> {
+        let (trait_ref, assoc_substs) =
+            projection.trait_ref_and_own_substs(self.def_id_visitor.tcx());
+        self.visit_trait(trait_ref)?;
+        if self.def_id_visitor.shallow() {
+            ControlFlow::CONTINUE
+        } else {
+            assoc_substs.iter().try_for_each(|subst| subst.visit_with(self))
+        }
+    }
+
     fn visit_predicate(&mut self, predicate: ty::Predicate<'tcx>) -> ControlFlow<V::BreakTy> {
         match predicate.kind().skip_binder() {
             ty::PredicateKind::Trait(ty::TraitPredicate { trait_ref }, _) => {
                 self.visit_trait(trait_ref)
             }
             ty::PredicateKind::Projection(ty::ProjectionPredicate { projection_ty, ty }) => {
                 ty.visit_with(self)?;
-                self.visit_trait(projection_ty.trait_ref(self.def_id_visitor.tcx()))
+                self.visit_projection_ty(projection_ty)
             }
             ty::PredicateKind::TypeOutlives(ty::OutlivesPredicate(ty, _region)) => {
                 ty.visit_with(self)
@@ -197,7 +217,7 @@ where
                     return ControlFlow::CONTINUE;
                 }
                 // This will also visit substs if necessary, so we don't need to recurse.
-                return self.visit_trait(proj.trait_ref(tcx));
+                return self.visit_projection_ty(proj);
             }
             ty::Dynamic(predicates, ..) => {
                 // All traits in the list are considered the "primary" part of the type
@@ -1204,10 +1224,9 @@ impl<'tcx> Visitor<'tcx> for TypePrivacyVisitor<'tcx> {
             }
 
             for (poly_predicate, _) in bounds.projection_bounds {
-                let tcx = self.tcx;
                 if self.visit(poly_predicate.skip_binder().ty).is_break()
                     || self
-                        .visit_trait(poly_predicate.skip_binder().projection_ty.trait_ref(tcx))
+                        .visit_projection_ty(poly_predicate.skip_binder().projection_ty)
                         .is_break()
                 {
                     return;

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -6,6 +6,7 @@ use rustc_errors::ErrorReported;
 use rustc_infer::traits::{TraitEngine, TraitEngineExt as _, TraitObligation};
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::error::ExpectedFound;
+use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::ToPredicate;
 use rustc_middle::ty::{self, Binder, Const, Ty, TypeFoldable};
 use std::marker::PhantomData;
@@ -633,9 +634,9 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                 // only reason we can fail to make progress on
                 // trait selection is because we don't have enough
                 // information about the types in the trait.
-                *stalled_on = trait_ref_infer_vars(
+                *stalled_on = substs_infer_vars(
                     self.selcx,
-                    trait_obligation.predicate.map_bound(|pred| pred.trait_ref),
+                    trait_obligation.predicate.map_bound(|pred| pred.trait_ref.substs),
                 );
 
                 debug!(
@@ -663,9 +664,9 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
         match project::poly_project_and_unify_type(self.selcx, &project_obligation) {
             Ok(Ok(Some(os))) => ProcessResult::Changed(mk_pending(os)),
             Ok(Ok(None)) => {
-                *stalled_on = trait_ref_infer_vars(
+                *stalled_on = substs_infer_vars(
                     self.selcx,
-                    project_obligation.predicate.to_poly_trait_ref(tcx),
+                    project_obligation.predicate.map_bound(|pred| pred.projection_ty.substs),
                 );
                 ProcessResult::Unchanged
             }
@@ -678,16 +679,15 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
     }
 }
 
-/// Returns the set of inference variables contained in a trait ref.
-fn trait_ref_infer_vars<'a, 'tcx>(
+/// Returns the set of inference variables contained in `substs`.
+fn substs_infer_vars<'a, 'tcx>(
     selcx: &mut SelectionContext<'a, 'tcx>,
-    trait_ref: ty::PolyTraitRef<'tcx>,
+    substs: ty::Binder<SubstsRef<'tcx>>,
 ) -> Vec<TyOrConstInferVar<'tcx>> {
     selcx
         .infcx()
-        .resolve_vars_if_possible(trait_ref)
-        .skip_binder()
-        .substs
+        .resolve_vars_if_possible(substs)
+        .skip_binder() // ok because this check doesn't care about regions
         .iter()
         // FIXME(eddyb) try using `skip_current_subtree` to skip everything that
         // doesn't contain inference variables, not just the outermost level.

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -292,11 +292,7 @@ fn predicate_references_self(
             //
             // This is ALT2 in issue #56288, see that for discussion of the
             // possible alternatives.
-            if data.projection_ty.trait_ref(tcx).substs[1..].iter().any(has_self_ty) {
-                Some(sp)
-            } else {
-                None
-            }
+            if data.projection_ty.substs[1..].iter().any(has_self_ty) { Some(sp) } else { None }
         }
         ty::PredicateKind::WellFormed(..)
         | ty::PredicateKind::ObjectSafe(..)

compiler/rustc_typeck/src/constrained_generic_params.rs

@@ -198,7 +198,7 @@ pub fn setup_constraining_predicates<'tcx>(
                 //     `<<T as Bar>::Baz as Iterator>::Output = <U as Iterator>::Output`
                 // Then the projection only applies if `T` is known, but it still
                 // does not determine `U`.
-                let inputs = parameters_for(&projection.projection_ty.trait_ref(tcx), true);
+                let inputs = parameters_for(&projection.projection_ty, true);
                 let relies_only_on_inputs = inputs.iter().all(|p| input_parameters.contains(&p));
                 if !relies_only_on_inputs {
                     continue;