Return structurally_normalize_ty and use Unnormalized::new_wip

Author: aapoalas

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -10,12 +10,12 @@ use rustc_hir::ItemKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::{self, InferCtxt, RegionResolutionError, SubregionOrigin, TyCtxtInferExt};
-use rustc_infer::traits::Obligation;
+use rustc_infer::traits::{Obligation, PredicateObligations};
 use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
 use rustc_middle::ty::print::PrintTraitRefExt as _;
 use rustc_middle::ty::relate::solver_relating::RelateExt;
 use rustc_middle::ty::{
-    self, Ty, TyCtxt, TypeVisitableExt, TypingMode, suggest_constraining_type_params,
+    self, Ty, TyCtxt, TypeVisitableExt, TypingMode, Unnormalized, suggest_constraining_type_params,
 };
 use rustc_span::{DUMMY_SP, Span, sym};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
@@ -465,6 +465,37 @@ fn visit_implementation_of_dispatch_from_dyn(checker: &Checker<'_>) -> Result<()
     }
 }
 
+fn structurally_normalize_ty<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    infcx: &InferCtxt<'tcx>,
+    impl_did: LocalDefId,
+    span: Span,
+    ty: Unnormalized<'tcx, Ty<'tcx>>,
+) -> Option<(Ty<'tcx>, PredicateObligations<'tcx>)> {
+    let ocx = ObligationCtxt::new(infcx);
+    let Ok(normalized_ty) = ocx.structurally_normalize_ty(
+        &traits::ObligationCause::misc(span, impl_did),
+        tcx.param_env(impl_did),
+        ty,
+    ) else {
+        // We shouldn't have errors here in the old solver, except for
+        // evaluate/fulfill mismatches, but that's not a reason for an ICE.
+        return None;
+    };
+    let errors = ocx.try_evaluate_obligations();
+    if !errors.is_empty() {
+        if infcx.next_trait_solver() {
+            unreachable!();
+        }
+        // We shouldn't have errors here in the old solver, except for
+        // evaluate/fulfill mismatches, but that's not a reason for an ICE.
+        debug!(?errors, "encountered errors while fulfilling");
+        return None;
+    }
+
+    Some((normalized_ty, ocx.into_pending_obligations()))
+}
+
 pub(crate) fn reborrow_info<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_did: LocalDefId,
@@ -583,7 +614,15 @@ pub(crate) fn coerce_shared_info<'tcx>(
     }
 
     assert_eq!(trait_ref.def_id, coerce_shared_trait);
-    let target = trait_ref.args.type_at(1);
+    let Some((target, _obligations)) = structurally_normalize_ty(
+        tcx,
+        &infcx,
+        impl_did,
+        span,
+        Unnormalized::new_wip(trait_ref.args.type_at(1)),
+    ) else {
+        todo!("something went wrong with structurally_normalize_ty");
+    };
 
     let param_env = tcx.param_env(impl_did);
     assert!(!source.has_escaping_bound_vars());