Structurally normalize in selection

compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs

@@ -5,7 +5,7 @@ use rustc_hir::def_id::DefId;
 use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
 use rustc_infer::traits::util::supertraits;
 use rustc_infer::traits::{
- Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult,
+ Obligation, PolyTraitObligation, PredicateObligation, Selection, SelectionResult, TraitEngine,
 };
 use rustc_middle::traits::solve::{CanonicalInput, Certainty, Goal};
 use rustc_middle::traits::{
@@ -20,6 +20,8 @@ use crate::solve::eval_ctxt::{EvalCtxt, GenerateProofTree};
 use crate::solve::inspect::ProofTreeBuilder;
 use crate::solve::search_graph::OverflowHandler;
 use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
+use crate::traits::StructurallyNormalizeExt;
+use crate::traits::TraitEngineExt;
 
 pub trait InferCtxtSelectExt<'tcx> {
  fn select_in_new_trait_solver(
@@ -228,18 +230,24 @@ fn rematch_object<'tcx>(
  goal: Goal<'tcx, ty::TraitPredicate<'tcx>>,
  mut nested: Vec<PredicateObligation<'tcx>>,
 ) -> SelectionResult<'tcx, Selection<'tcx>> {
- let self_ty = goal.predicate.self_ty();
- let ty::Dynamic(data, _, source_kind) = *self_ty.kind() else { bug!() };
- let source_trait_ref = data.principal().unwrap().with_self_ty(infcx.tcx, self_ty);
+ let a_ty = structurally_normalize(goal.predicate.self_ty(), infcx, goal.param_env, &mut nested);
+ let ty::Dynamic(data, _, source_kind) = *a_ty.kind() else { bug!() };
+ let source_trait_ref = data.principal().unwrap().with_self_ty(infcx.tcx, a_ty);
 
  let (is_upcasting, target_trait_ref_unnormalized) =
  if Some(goal.predicate.def_id()) == infcx.tcx.lang_items().unsize_trait() {
  assert_eq!(source_kind, ty::Dyn, "cannot upcast dyn*");
- if let ty::Dynamic(data, _, ty::Dyn) = goal.predicate.trait_ref.args.type_at(1).kind() {
+ let b_ty = structurally_normalize(
+ goal.predicate.trait_ref.args.type_at(1),
+ infcx,
+ goal.param_env,
+ &mut nested,
+ );
+ if let ty::Dynamic(data, _, ty::Dyn) = *b_ty.kind() {
  // FIXME: We also need to ensure that the source lifetime outlives the
  // target lifetime. This doesn't matter for codegen, though, and only
  // *really* matters if the goal's certainty is ambiguous.
- (true, data.principal().unwrap().with_self_ty(infcx.tcx, self_ty))
+ (true, data.principal().unwrap().with_self_ty(infcx.tcx, a_ty))
  } else {
  bug!()
  }
@@ -447,3 +455,22 @@ fn rematch_unsize<'tcx>(
 
  Ok(Some(ImplSource::Builtin(nested)))
 }
+
+fn structurally_normalize<'tcx>(
+ ty: Ty<'tcx>,
+ infcx: &InferCtxt<'tcx>,
+ param_env: ty::ParamEnv<'tcx>,
+ nested: &mut Vec<PredicateObligation<'tcx>>,
+) -> Ty<'tcx> {
+ if matches!(ty.kind(), ty::Alias(..)) {
+ let mut engine = <dyn TraitEngine<'tcx>>::new(infcx);
+ let normalized_ty = infcx
+ .at(&ObligationCause::dummy(), param_env)
+ .structurally_normalize(ty, &mut *engine)
+ .expect("normalization shouldn't fail if we got to here");
+ nested.extend(engine.pending_obligations());
+ normalized_ty
+ } else {
+ ty
+ }
+}

tests/ui/traits/new-solver/trait-upcast-lhs-needs-normalization.rs

@@ -0,0 +1,18 @@
+// check-pass
+// compile-flags: -Ztrait-solver=next
+
+pub trait A {}
+pub trait B: A {}
+
+pub trait Mirror {
+ type Assoc: ?Sized;
+}
+impl<T: ?Sized> Mirror for T {
+ type Assoc = T;
+}
+
+pub fn foo<'a>(x: &'a <dyn B + 'static as Mirror>::Assoc) -> &'a (dyn A + 'static) {
+ x
+}
+
+fn main() {}