Be better about bound vars

Author: compiler-errors

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -290,7 +290,7 @@ impl DeepRejectCtxt {
             // Impls cannot contain these types as these cannot be named directly.
             ty::FnDef(..) | ty::Closure(..) | ty::Generator(..) => false,
 
-            ty::Placeholder(..) => false,
+            ty::Placeholder(..) | ty::Bound(..) => false,
 
             // Depending on the value of `treat_obligation_params`, we either
             // treat generic parameters like placeholders or like inference variables.
@@ -310,7 +310,7 @@ impl DeepRejectCtxt {
 
             ty::Error(_) => true,
 
-            ty::GeneratorWitness(..) | ty::GeneratorWitnessMIR(..) | ty::Bound(..) => {
+            ty::GeneratorWitness(..) | ty::GeneratorWitnessMIR(..) => {
                 bug!("unexpected obligation type: {:?}", obligation_ty)
             }
         }

compiler/rustc_trait_selection/src/traits/error_reporting/on_unimplemented.rs

@@ -60,7 +60,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     ) -> Option<(DefId, SubstsRef<'tcx>)> {
         let tcx = self.tcx;
         let param_env = obligation.param_env;
-        let trait_ref = tcx.erase_late_bound_regions(trait_ref);
+        let trait_ref = self.instantiate_binder_with_placeholders(trait_ref);
         let trait_self_ty = trait_ref.self_ty();
 
         let mut self_match_impls = vec![];

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1060,7 +1060,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> bool {
         let self_ty = self.resolve_vars_if_possible(trait_pred.self_ty());
-        let ty = self.tcx.erase_late_bound_regions(self_ty);
+        let ty = self.instantiate_binder_with_placeholders(self_ty);
         let Some(generics) = self.tcx.hir().get_generics(obligation.cause.body_id) else { return false };
         let ty::Ref(_, inner_ty, hir::Mutability::Not) = ty.kind() else { return false };
         let ty::Param(param) = inner_ty.kind() else { return false };

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -396,7 +396,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     // still be provided by a manual implementation for
                     // this trait and type.
                 }
-                ty::Param(..) | ty::Alias(ty::Projection, ..) => {
+                ty::Param(..)
+                | ty::Alias(ty::Projection, ..)
+                | ty::Placeholder(..)
+                | ty::Bound(..) => {
                     // In these cases, we don't know what the actual
                     // type is. Therefore, we cannot break it down
                     // into its constituent types. So we don't
@@ -448,6 +451,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         );
 
         self.infcx.probe(|_snapshot| {
+            if obligation.has_non_region_late_bound() {
+                return;
+            }
+
             // The code below doesn't care about regions, and the
             // self-ty here doesn't escape this probe, so just erase
             // any LBR.