add AliasEq to PredicateKind

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -823,14 +823,17 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                         _ => return false,
                     }
                 }
+
                 // There's not really much we can do with these predicates -
                 // we start out with a `ParamEnv` with no inference variables,
                 // and these don't correspond to adding any new bounds to
                 // the `ParamEnv`.
                 ty::PredicateKind::WellFormed(..)
+                | ty::PredicateKind::AliasEq(..)
                 | ty::PredicateKind::ObjectSafe(..)
                 | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::Subtype(..)
+                // FIXME(generic_const_exprs): you can absolutely add this as a where clauses
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::Coerce(..)
                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => {}

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

@@ -1278,6 +1278,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         span,
                         "TypeWellFormedFromEnv predicate should only exist in the environment"
                     ),
+
+                    ty::PredicateKind::AliasEq(..) => span_bug!(
+                        span,
+                        "AliasEq predicate should never be the predicate cause of a SelectionError"
+                    ),
                 }
             }
 

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -328,6 +328,9 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for Chalk")
                 }
+                ty::PredicateKind::AliasEq(..) => {
+                    bug!("AliasEq is only used for new solver")
+                }
             },
             Some(pred) => match pred {
                 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => {
@@ -594,6 +597,9 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for Chalk")
                 }
+                ty::PredicateKind::AliasEq(..) => {
+                    bug!("AliasEq is only used for new solver")
+                }
             },
         }
     }

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -327,6 +327,8 @@ fn predicate_references_self<'tcx>(
             // possible alternatives.
             if data.projection_ty.substs[1..].iter().any(has_self_ty) { Some(sp) } else { None }
         }
+        ty::PredicateKind::AliasEq(..) => bug!("`AliasEq` not allowed as assumption"),
+
         ty::PredicateKind::WellFormed(..)
         | ty::PredicateKind::ObjectSafe(..)
         | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
@@ -334,6 +336,7 @@ fn predicate_references_self<'tcx>(
         | ty::PredicateKind::ClosureKind(..)
         | ty::PredicateKind::Subtype(..)
         | ty::PredicateKind::Coerce(..)
+        // FIXME(generic_const_exprs): this can mention `Self`
         | ty::PredicateKind::ConstEvaluatable(..)
         | ty::PredicateKind::ConstEquate(..)
         | ty::PredicateKind::Ambiguous
@@ -368,6 +371,7 @@ fn generics_require_sized_self(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
             | ty::PredicateKind::Clause(ty::Clause::TypeOutlives(..))
             | ty::PredicateKind::ConstEvaluatable(..)
             | ty::PredicateKind::ConstEquate(..)
+            | ty::PredicateKind::AliasEq(..)
             | ty::PredicateKind::Ambiguous
             | ty::PredicateKind::TypeWellFormedFromEnv(..) => false,
         }

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

@@ -991,6 +991,9 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for chalk")
                 }
+                ty::PredicateKind::AliasEq(..) => {
+                    bug!("AliasEq is only used for new solver")
+                }
                 ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
             }
         })

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -187,6 +187,9 @@ pub fn predicate_obligations<'tcx>(
         ty::PredicateKind::TypeWellFormedFromEnv(..) => {
             bug!("TypeWellFormedFromEnv is only used for Chalk")
         }
+        ty::PredicateKind::AliasEq(..) => {
+            bug!("We should only wf check where clauses and `AliasEq` is not a `Clause`")
+        }
     }
 
     wf.normalize(infcx)
@@ -928,6 +931,7 @@ pub(crate) fn required_region_bounds<'tcx>(
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..)
                 | ty::PredicateKind::Ambiguous
+                | ty::PredicateKind::AliasEq(..)
                 | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
                 ty::PredicateKind::Clause(ty::Clause::TypeOutlives(ty::OutlivesPredicate(
                     ref t,