Combine projection and opaque into alias

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -697,7 +697,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     .map_bound(|p| p.predicates),
                 None,
             ),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 find_fn_kind_from_did(tcx.bound_explicit_item_bounds(*def_id), Some(*substs))
             }
             ty::Closure(_, substs) => match substs.as_closure().kind() {

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -504,7 +504,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         let ErrorConstraintInfo { outlived_fr, span, .. } = errci;
 
         let mut output_ty = self.regioncx.universal_regions().unnormalized_output_ty;
-        if let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = *output_ty.kind() {
+        if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = *output_ty.kind() {
             output_ty = self.infcx.tcx.type_of(def_id)
         };
 

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -411,9 +411,9 @@ fn push_debuginfo_type_name<'tcx>(
         ty::Error(_)
         | ty::Infer(_)
         | ty::Placeholder(..)
-        | ty::Projection(..)
+        | ty::Alias(ty::Projection, ..)
         | ty::Bound(..)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::GeneratorWitness(..) => {
             bug!(
                 "debuginfo: Trying to create type name for \

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -142,12 +142,12 @@ pub(crate) fn const_to_valtree_inner<'tcx>(
         | ty::Foreign(..)
         | ty::Infer(ty::FreshIntTy(_))
         | ty::Infer(ty::FreshFloatTy(_))
-        | ty::Projection(..)
+        | ty::Alias(ty::Projection, ..)
         | ty::Param(_)
         | ty::Bound(..)
         | ty::Placeholder(..)
         // FIXME(oli-obk): we could look behind opaque types
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Infer(_)
         // FIXME(oli-obk): we can probably encode closures just like structs
         | ty::Closure(..)
@@ -307,11 +307,11 @@ pub fn valtree_to_const_value<'tcx>(
         | ty::Foreign(..)
         | ty::Infer(ty::FreshIntTy(_))
         | ty::Infer(ty::FreshFloatTy(_))
-        | ty::Projection(..)
+        | ty::Alias(ty::Projection, ..)
         | ty::Param(_)
         | ty::Bound(..)
         | ty::Placeholder(..)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Infer(_)
         | ty::Closure(..)
         | ty::Generator(..)

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -82,8 +82,8 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
             ty::Adt(ref adt, _) => {
                 ConstValue::from_machine_usize(adt.variants().len() as u64, &tcx)
             }
-            ty::Projection(_)
+            ty::Alias(ty::Projection, _)
-            | ty::Opaque(ty::AliasTy { def_id: _, substs: _ })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs: _ })
             | ty::Param(_)
             | ty::Placeholder(_)
             | ty::Infer(_) => throw_inval!(TooGeneric),

compiler/rustc_const_eval/src/interpret/validity.rs

@@ -601,8 +601,8 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
             | ty::Placeholder(..)
             | ty::Bound(..)
             | ty::Param(..)
-            | ty::Opaque(..)
+            | ty::Alias(ty::Opaque, ..)
-            | ty::Projection(..)
+            | ty::Alias(ty::Projection, ..)
             | ty::GeneratorWitness(..) => bug!("Encountered invalid type {:?}", ty),
         }
     }

compiler/rustc_const_eval/src/transform/validate.rs

@@ -241,7 +241,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 };
 
                 let kind = match parent_ty.ty.kind() {
-                    &ty::Opaque(ty::AliasTy { def_id, substs }) => {
+                    &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                         self.tcx.bound_type_of(def_id).subst(self.tcx, substs).kind()
                     }
                     kind => kind,
@@ -652,7 +652,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     self.fail(location, "`SetDiscriminant`is not allowed until deaggregation");
                 }
                 let pty = place.ty(&self.body.local_decls, self.tcx).ty.kind();
-                if !matches!(pty, ty::Adt(..) | ty::Generator(..) | ty::Opaque(..)) {
+                if !matches!(pty, ty::Adt(..) | ty::Generator(..) | ty::Alias(ty::Opaque, ..)) {
                     self.fail(
                         location,
                         format!(

compiler/rustc_const_eval/src/util/type_name.rs

@@ -58,8 +58,8 @@ impl<'tcx> Printer<'tcx> for AbsolutePathPrinter<'tcx> {
             // Types with identity (print the module path).
             ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did: def_id, .. }, _)), substs)
             | ty::FnDef(def_id, substs)
-            | ty::Opaque(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs })
-            | ty::Projection(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Projection, ty::AliasTy { def_id, substs })
             | ty::Closure(def_id, substs)
             | ty::Generator(def_id, substs, _) => self.print_def_path(def_id, substs),
             ty::Foreign(def_id) => self.print_def_path(def_id, &[]),

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1241,7 +1241,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 //
                 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
                 // parameter to have a skipped binder.
-                let param_ty = tcx.mk_ty(ty::Projection(projection_ty.skip_binder()));
+                let param_ty = tcx.mk_ty(ty::Alias(ty::Projection, projection_ty.skip_binder()));
                 self.add_bounds(param_ty, ast_bounds.iter(), bounds, candidate.bound_vars());
             }
         }

compiler/rustc_hir_analysis/src/check/check.rs

@@ -1440,7 +1440,7 @@ fn opaque_type_cycle_error(tcx: TyCtxt<'_>, def_id: LocalDefId, span: Span) -> E
                 impl<'tcx> ty::visit::TypeVisitor<'tcx> for OpaqueTypeCollector {
                     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                         match *t.kind() {
-                            ty::Opaque(ty::AliasTy { def_id: def, substs: _ }) => {
+                            ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, substs: _ }) => {
                                 self.0.push(def);
                                 ControlFlow::CONTINUE
                             }

compiler/rustc_hir_analysis/src/check/compare_method.rs

@@ -571,7 +571,7 @@ impl<'tcx> TypeFolder<'tcx> for ImplTraitInTraitCollector<'_, 'tcx> {
     }
 
     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        if let ty::Projection(proj) = ty.kind()
+        if let ty::Alias(ty::Projection, proj) = ty.kind()
             && self.tcx().def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
         {
             if let Some((ty, _)) = self.types.get(&proj.def_id) {
@@ -1734,7 +1734,7 @@ pub fn check_type_bounds<'tcx>(
     let normalize_param_env = {
         let mut predicates = param_env.caller_bounds().iter().collect::<Vec<_>>();
         match impl_ty_value.kind() {
-            ty::Projection(proj)
+            ty::Alias(ty::Projection, proj)
                 if proj.def_id == trait_ty.def_id && proj.substs == rebased_substs =>
             {
                 // Don't include this predicate if the projected type is

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -759,7 +759,7 @@ impl<'tcx> TypeVisitor<'tcx> for GATSubstCollector<'tcx> {
 
     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match t.kind() {
-            ty::Projection(p) if p.def_id == self.gat => {
+            ty::Alias(ty::Projection, p) if p.def_id == self.gat => {
                 for (idx, subst) in p.substs.iter().enumerate() {
                     match subst.unpack() {
                         GenericArgKind::Lifetime(lt) if !lt.is_late_bound() => {
@@ -1592,7 +1592,7 @@ fn check_return_position_impl_trait_in_trait_bounds<'tcx>(
     {
         for arg in fn_output.walk() {
             if let ty::GenericArgKind::Type(ty) = arg.unpack()
-                && let ty::Projection(proj) = ty.kind()
+                && let ty::Alias(ty::Projection, proj) = ty.kind()
                 && tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
                 && tcx.impl_trait_in_trait_parent(proj.def_id) == fn_def_id.to_def_id()
             {

compiler/rustc_hir_analysis/src/coherence/inherent_impls.rs

@@ -223,7 +223,7 @@ impl<'tcx> InherentCollect<'tcx> {
             | ty::Tuple(..) => {
                 self.check_primitive_impl(item.owner_id.def_id, self_ty, items, ty.span)
             }
-            ty::Projection(..) | ty::Opaque(..) | ty::Param(_) => {
+            ty::Alias(ty::Projection, ..) | ty::Alias(ty::Opaque, ..) | ty::Param(_) => {
                 let mut err = struct_span_err!(
                     self.tcx.sess,
                     ty.span,

compiler/rustc_hir_analysis/src/collect/lifetimes.rs

@@ -1749,7 +1749,7 @@ fn is_late_bound_map(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<&FxIndexSet<
                 ty::Param(param_ty) => {
                     self.arg_is_constrained[param_ty.index as usize] = true;
                 }
-                ty::Projection(_) => return ControlFlow::Continue(()),
+                ty::Alias(ty::Projection, _) => return ControlFlow::Continue(()),
                 _ => (),
             }
             t.super_visit_with(self)

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -411,7 +411,7 @@ pub(super) fn explicit_predicates_of<'tcx>(
             //       substs are the same as the trait's.
             // * It must be an associated type for this trait (*not* a
             //   supertrait).
-            if let ty::Projection(projection) = ty.kind() {
+            if let ty::Alias(ty::Projection, projection) = ty.kind() {
                 projection.substs == trait_identity_substs
                     && tcx.associated_item(projection.def_id).container_id(tcx) == def_id
             } else {

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -52,7 +52,7 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
             // Using the ItemCtxt convert the HIR for the unresolved assoc type into a
             // ty which is a fully resolved projection.
             // For the code example above, this would mean converting Self::Assoc<3>
-            // into a ty::Projection(<Self as Foo>::Assoc<3>)
+            // into a ty::Alias(ty::Projection, <Self as Foo>::Assoc<3>)
             let item_hir_id = tcx
                 .hir()
                 .parent_iter(hir_id)
@@ -68,7 +68,7 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
             // the def_id that this query was called with. We filter to only type and const args here
             // as a precaution for if it's ever allowed to elide lifetimes in GAT's. It currently isn't
             // but it can't hurt to be safe ^^
-            if let ty::Projection(projection) = ty.kind() {
+            if let ty::Alias(ty::Projection, projection) = ty.kind() {
                 let generics = tcx.generics_of(projection.def_id);
 
                 let arg_index = segment

compiler/rustc_hir_analysis/src/constrained_generic_params.rs

@@ -59,7 +59,7 @@ struct ParameterCollector {
 impl<'tcx> TypeVisitor<'tcx> for ParameterCollector {
     fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
         match *t.kind() {
-            ty::Projection(..) if !self.include_nonconstraining => {
+            ty::Alias(ty::Projection, ..) if !self.include_nonconstraining => {
                 // projections are not injective
                 return ControlFlow::CONTINUE;
             }

compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs

@@ -196,7 +196,7 @@ fn insert_required_predicates_to_be_wf<'tcx>(
                 }
             }
 
-            ty::Projection(obj) => {
+            ty::Alias(ty::Projection, obj) => {
                 // This corresponds to `<T as Foo<'a>>::Bar`. In this case, we should use the
                 // explicit predicates as well.
                 debug!("Projection");

compiler/rustc_hir_analysis/src/variance/constraints.rs

@@ -249,11 +249,11 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 self.add_constraints_from_substs(current, def.did(), substs, variance);
             }
 
-            ty::Projection(ref data) => {
+            ty::Alias(ty::Projection, ref data) => {
                 self.add_constraints_from_invariant_substs(current, data.substs, variance);
             }
 
-            ty::Opaque(ty::AliasTy { def_id: _, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs }) => {
                 self.add_constraints_from_invariant_substs(current, substs, variance);
             }
 

compiler/rustc_hir_analysis/src/variance/mod.rs

@@ -112,8 +112,8 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
         fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
             // FIXME(alias): merge these
             match t.kind() {
-                ty::Opaque(ty::AliasTy { def_id, substs }) => self.visit_opaque(*def_id, substs),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => self.visit_opaque(*def_id, substs),
-                ty::Projection(proj)
+                ty::Alias(ty::Projection, proj)
                     if self.tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder =>
                 {
                     self.visit_opaque(proj.def_id, proj.substs)

compiler/rustc_hir_typeck/src/_match.rs

@@ -212,7 +212,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 self.can_coerce(arm_ty, ret_ty)
                     && prior_arm.map_or(true, |(_, ty, _)| self.can_coerce(ty, ret_ty))
                     // The match arms need to unify for the case of `impl Trait`.
-                    && !matches!(ret_ty.kind(), ty::Opaque(..))
+                    && !matches!(ret_ty.kind(), ty::Alias(ty::Opaque, ..))
             }
             _ => false,
         };
@@ -518,7 +518,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 let substs = sig.output().walk().find_map(|arg| {
                     if let ty::GenericArgKind::Type(ty) = arg.unpack()
-                        && let ty::Opaque(ty::AliasTy { def_id, substs }) = *ty.kind()
+                        && let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) = *ty.kind()
                         && def_id == rpit_def_id
                     {
                         Some(substs)

compiler/rustc_hir_typeck/src/cast.rs

@@ -118,8 +118,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Pointers to foreign types are thin, despite being unsized
             ty::Foreign(..) => Some(PointerKind::Thin),
             // We should really try to normalize here.
-            ty::Projection(pi) => Some(PointerKind::OfProjection(pi)),
+            ty::Alias(ty::Projection, pi) => Some(PointerKind::OfProjection(pi)),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 Some(PointerKind::OfOpaque(def_id, substs))
             }
             ty::Param(p) => Some(PointerKind::OfParam(p)),

compiler/rustc_hir_typeck/src/closure.rs

@@ -167,9 +167,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected_ty: Ty<'tcx>,
     ) -> (Option<ExpectedSig<'tcx>>, Option<ty::ClosureKind>) {
         match *expected_ty.kind() {
-            ty::Opaque(ty::AliasTy { def_id, substs }) => self.deduce_signature_from_predicates(
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => self
-                self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
+                .deduce_signature_from_predicates(
-            ),
+                    self.tcx.bound_explicit_item_bounds(def_id).subst_iter_copied(self.tcx, substs),
+                ),
             ty::Dynamic(ref object_type, ..) => {
                 let sig = object_type.projection_bounds().find_map(|pb| {
                     let pb = pb.with_self_ty(self.tcx, self.tcx.types.trait_object_dummy_self);
@@ -677,13 +678,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     get_future_output(obligation.predicate, obligation.cause.span)
                 })?
             }
-            ty::Opaque(ty::AliasTy { def_id, substs }) => self
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => self
                 .tcx
                 .bound_explicit_item_bounds(def_id)
                 .subst_iter_copied(self.tcx, substs)
                 .find_map(|(p, s)| get_future_output(p, s))?,
             ty::Error(_) => return None,
-            ty::Projection(proj)
+            ty::Alias(ty::Projection, proj)
                 if self.tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder =>
             {
                 self.tcx

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1805,7 +1805,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
         {
             let ty = <dyn AstConv<'_>>::ast_ty_to_ty(fcx, ty);
             // Get the `impl Trait`'s `DefId`.
-            if let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = ty.kind()
+            if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = ty.kind()
                 // Get the `impl Trait`'s `Item` so that we can get its trait bounds and
                 // get the `Trait`'s `DefId`.
                 && let hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, .. }) =

compiler/rustc_hir_typeck/src/expr.rs

@@ -2391,7 +2391,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ty::Param(param_ty) => {
                 self.point_at_param_definition(&mut err, param_ty);
             }
-            ty::Opaque(ty::AliasTy { def_id: _, substs: _ }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs: _ }) => {
                 self.suggest_await_on_field_access(&mut err, ident, base, base_ty.peel_refs());
             }
             _ => {}

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -716,7 +716,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if formal_ret.has_infer_types() {
             for ty in ret_ty.walk() {
                 if let ty::subst::GenericArgKind::Type(ty) = ty.unpack()
-                    && let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = *ty.kind()
+                    && let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = *ty.kind()
                     && let Some(def_id) = def_id.as_local()
                     && self.opaque_type_origin(def_id, DUMMY_SP).is_some() {
                     return None;

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -2124,7 +2124,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                     }
                 }
-                ty::Opaque(ty::AliasTy { def_id: new_def_id, substs: _ })
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: new_def_id, substs: _ })
                 | ty::Closure(new_def_id, _)
                 | ty::FnDef(new_def_id, _) => {
                     def_id = new_def_id;
@@ -2217,7 +2217,7 @@ fn find_param_in_ty<'tcx>(ty: Ty<'tcx>, param_to_point_at: ty::GenericArg<'tcx>)
         if arg == param_to_point_at {
             return true;
         } else if let ty::GenericArgKind::Type(ty) = arg.unpack()
-            && let ty::Projection(..) = ty.kind()
+            && let ty::Alias(ty::Projection, ..) = ty.kind()
         {
             // This logic may seem a bit strange, but typically when
             // we have a projection type in a function signature, the

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -174,7 +174,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let fn_sig = substs.as_closure().sig();
                     Some((DefIdOrName::DefId(def_id), fn_sig.output(), fn_sig.inputs().map_bound(|inputs| &inputs[1..])))
                 }
-                ty::Opaque(ty::AliasTy { def_id, substs }) => {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                     self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
                         if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
                         && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()

compiler/rustc_hir_typeck/src/generator_interior/mod.rs

@@ -563,7 +563,7 @@ fn check_must_not_suspend_ty<'tcx>(
         }
         ty::Adt(def, _) => check_must_not_suspend_def(fcx.tcx, def.did(), hir_id, data),
         // FIXME: support adding the attribute to TAITs
-        ty::Opaque(ty::AliasTy { def_id: def, substs: _ }) => {
+        ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, substs: _ }) => {
             let mut has_emitted = false;
             for &(predicate, _) in fcx.tcx.explicit_item_bounds(def) {
                 // We only look at the `DefId`, so it is safe to skip the binder here.

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -1969,7 +1969,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         | ty::Float(_)
                         | ty::Adt(_, _)
                         | ty::Str
-                        | ty::Projection(_)
+                        | ty::Alias(ty::Projection, _)
                         | ty::Param(_) => format!("{deref_ty}"),
                         // we need to test something like  <&[_]>::len or <(&[u32])>::len
                         // and Vec::function();

compiler/rustc_hir_typeck/src/writeback.rs

@@ -546,7 +546,7 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
             impl<'tcx> ty::TypeVisitor<'tcx> for RecursionChecker {
                 type BreakTy = ();
                 fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-                    if let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = *t.kind() {
+                    if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = *t.kind() {
                         if def_id == self.def_id.to_def_id() {
                             return ControlFlow::Break(());
                         }

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -453,10 +453,10 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
             | ty::Dynamic(..)
             | ty::Never
             | ty::Tuple(..)
-            | ty::Projection(..)
+            | ty::Alias(ty::Projection, ..)
             | ty::Foreign(..)
             | ty::Param(..)
-            | ty::Opaque(..) => {
+            | ty::Alias(ty::Opaque, ..) => {
                 if t.flags().intersects(self.needs_canonical_flags) {
                     t.super_fold_with(self)
                 } else {

compiler/rustc_infer/src/infer/combine.rs

@@ -675,7 +675,7 @@ impl<'tcx> TypeRelation<'tcx> for Generalizer<'_, 'tcx> {
                 // relatable.
                 Ok(t)
             }
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 let s = self.relate(substs, substs)?;
                 Ok(if s == substs { t } else { self.infcx.tcx.mk_opaque(def_id, s) })
             }

compiler/rustc_infer/src/infer/equate.rs

@@ -101,13 +101,13 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
             }
 
             (
-                &ty::Opaque(ty::AliasTy { def_id: a_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: _ }),
-                &ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: _ }),
             ) if a_def_id == b_def_id => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;
             }
-            (&ty::Opaque(ty::AliasTy { def_id, substs: _ }), _)
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }), _)
-            | (_, &ty::Opaque(ty::AliasTy { def_id, substs: _ }))
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }))
                 if self.fields.define_opaque_types && def_id.is_local() =>
             {
                 self.fields.obligations.extend(

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -340,8 +340,8 @@ impl<'tcx> InferCtxt<'tcx> {
     pub fn get_impl_future_output_ty(&self, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
         // FIXME(alias): Merge these
         let (def_id, substs) = match *ty.kind() {
-            ty::Opaque(ty::AliasTy { def_id, substs }) => (def_id, substs),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => (def_id, substs),
-            ty::Projection(data)
+            ty::Alias(ty::Projection, data)
                 if self.tcx.def_kind(data.def_id) == DefKind::ImplTraitPlaceholder =>
             {
                 (data.def_id, data.substs)
@@ -1732,7 +1732,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     let sort_string = |ty: Ty<'tcx>, path: Option<PathBuf>| {
                         // FIXME(alias): Merge these
                         let mut s = match (extra, ty.kind()) {
-                            (true, ty::Opaque(ty::AliasTy { def_id, .. })) => {
+                            (true, ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. })) => {
                                 let sm = self.tcx.sess.source_map();
                                 let pos = sm.lookup_char_pos(self.tcx.def_span(*def_id).lo());
                                 format!(
@@ -1742,7 +1742,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                     pos.col.to_usize() + 1,
                                 )
                             }
-                            (true, ty::Projection(proj))
+                            (true, ty::Alias(ty::Projection, proj))
                                 if self.tcx.def_kind(proj.def_id)
                                     == DefKind::ImplTraitPlaceholder =>
                             {
@@ -2385,10 +2385,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                         // fn get_later<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
                         // suggest:
                         // fn get_later<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a
-                        ty::Closure(_, _substs)
+                        ty::Closure(..) | ty::Alias(ty::Opaque, ..) if return_impl_trait => {
-                        | ty::Opaque(ty::AliasTy { def_id: _, substs: _substs })
-                            if return_impl_trait =>
-                        {
                             new_binding_suggestion(&mut err, type_param_span);
                         }
                         _ => {
@@ -2770,7 +2767,9 @@ impl TyCategory {
     pub fn from_ty(tcx: TyCtxt<'_>, ty: Ty<'_>) -> Option<(Self, DefId)> {
         match *ty.kind() {
             ty::Closure(def_id, _) => Some((Self::Closure, def_id)),
-            ty::Opaque(ty::AliasTy { def_id, substs: _ }) => Some((Self::Opaque, def_id)),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) => {
+                Some((Self::Opaque, def_id))
+            }
             ty::Generator(def_id, ..) => {
                 Some((Self::Generator(tcx.generator_kind(def_id).unwrap()), def_id))
             }

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -852,7 +852,10 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
             match inner.unpack() {
                 GenericArgKind::Lifetime(_) => {}
                 GenericArgKind::Type(ty) => {
-                    if matches!(ty.kind(), ty::Opaque(..) | ty::Closure(..) | ty::Generator(..)) {
+                    if matches!(
+                        ty.kind(),
+                        ty::Alias(ty::Opaque, ..) | ty::Closure(..) | ty::Generator(..)
+                    ) {
                         // Opaque types can't be named by the user right now.
                         //
                         // Both the generic arguments of closures and generators can

compiler/rustc_infer/src/infer/error_reporting/suggest.rs

@@ -487,12 +487,12 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                 StatementAsExpression::CorrectType
             }
             (
-                ty::Opaque(ty::AliasTy { def_id: last_def_id, substs: _ }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, substs: _ }),
-                ty::Opaque(ty::AliasTy { def_id: exp_def_id, substs: _ }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, substs: _ }),
             ) if last_def_id == exp_def_id => StatementAsExpression::CorrectType,
             (
-                ty::Opaque(ty::AliasTy { def_id: last_def_id, substs: last_bounds }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: last_def_id, substs: last_bounds }),
-                ty::Opaque(ty::AliasTy { def_id: exp_def_id, substs: exp_bounds }),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: exp_def_id, substs: exp_bounds }),
             ) => {
                 debug!(
                     "both opaque, likely future {:?} {:?} {:?} {:?}",

compiler/rustc_infer/src/infer/freshen.rs

@@ -205,12 +205,11 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
             | ty::Dynamic(..)
             | ty::Never
             | ty::Tuple(..)
-            | ty::Projection(..)
+            | ty::Alias(..)
             | ty::Foreign(..)
             | ty::Param(..)
             | ty::Closure(..)
-            | ty::GeneratorWitness(..)
+            | ty::GeneratorWitness(..) => t.super_fold_with(self),
-            | ty::Opaque(..) => t.super_fold_with(self),
 
             ty::Placeholder(..) | ty::Bound(..) => bug!("unexpected type {:?}", t),
         }

compiler/rustc_infer/src/infer/lattice.rs

@@ -106,11 +106,11 @@ where
         }
 
         (
-            &ty::Opaque(ty::AliasTy { def_id: a_def_id, substs: _ }),
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: _ }),
-            &ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: _ }),
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: _ }),
         ) if a_def_id == b_def_id => infcx.super_combine_tys(this, a, b),
-        (&ty::Opaque(ty::AliasTy { def_id, substs: _ }), _)
+        (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }), _)
-        | (_, &ty::Opaque(ty::AliasTy { def_id, substs: _ }))
+        | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }))
             if this.define_opaque_types() && def_id.is_local() =>
         {
             this.add_obligations(

compiler/rustc_infer/src/infer/nll_relate/mod.rs

@@ -281,7 +281,7 @@ where
         use rustc_span::DUMMY_SP;
 
         match *value_ty.kind() {
-            ty::Projection(other_projection_ty) => {
+            ty::Alias(ty::Projection, other_projection_ty) => {
                 let var = self.infcx.next_ty_var(TypeVariableOrigin {
                     kind: TypeVariableOriginKind::MiscVariable,
                     span: DUMMY_SP,
@@ -335,7 +335,9 @@ where
                 return Ok(value_ty);
             }
 
-            ty::Projection(projection_ty) if D::normalization() == NormalizationStrategy::Lazy => {
+            ty::Alias(ty::Projection, projection_ty)
+                if D::normalization() == NormalizationStrategy::Lazy =>
+            {
                 return Ok(self.relate_projection_ty(projection_ty, self.infcx.tcx.mk_ty_var(vid)));
             }
 
@@ -406,8 +408,8 @@ where
             }
         };
         let (a, b) = match (a.kind(), b.kind()) {
-            (&ty::Opaque(..), _) => (a, generalize(b, false)?),
+            (&ty::Alias(ty::Opaque, ..), _) => (a, generalize(b, false)?),
-            (_, &ty::Opaque(..)) => (generalize(a, true)?, b),
+            (_, &ty::Alias(ty::Opaque, ..)) => (generalize(a, true)?, b),
             _ => unreachable!(),
         };
         let cause = ObligationCause::dummy_with_span(self.delegate.span());
@@ -609,8 +611,8 @@ where
             (&ty::Infer(ty::TyVar(vid)), _) => self.relate_ty_var((vid, b)),
 
             (
-                &ty::Opaque(ty::AliasTy { def_id: a_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: _ }),
-                &ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: _ }),
             ) if a_def_id == b_def_id => infcx.super_combine_tys(self, a, b).or_else(|err| {
                 self.tcx().sess.delay_span_bug(
                     self.delegate.span(),
@@ -618,20 +620,20 @@ where
                 );
                 if a_def_id.is_local() { self.relate_opaques(a, b) } else { Err(err) }
             }),
-            (&ty::Opaque(ty::AliasTy { def_id, substs: _ }), _)
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }), _)
-            | (_, &ty::Opaque(ty::AliasTy { def_id, substs: _ }))
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }))
                 if def_id.is_local() =>
             {
                 self.relate_opaques(a, b)
             }
 
-            (&ty::Projection(projection_ty), _)
+            (&ty::Alias(ty::Projection, projection_ty), _)
                 if D::normalization() == NormalizationStrategy::Lazy =>
             {
                 Ok(self.relate_projection_ty(projection_ty, b))
             }
 
-            (_, &ty::Projection(projection_ty))
+            (_, &ty::Alias(ty::Projection, projection_ty))
                 if D::normalization() == NormalizationStrategy::Lazy =>
             {
                 Ok(self.relate_projection_ty(projection_ty, a))

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -66,7 +66,7 @@ impl<'tcx> InferCtxt<'tcx> {
             lt_op: |lt| lt,
             ct_op: |ct| ct,
             ty_op: |ty| match *ty.kind() {
-                ty::Opaque(ty::AliasTy { def_id, substs: _substs })
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ })
                     if replace_opaque_type(def_id) =>
                 {
                     let def_span = self.tcx.def_span(def_id);
@@ -106,7 +106,7 @@ impl<'tcx> InferCtxt<'tcx> {
         }
         let (a, b) = if a_is_expected { (a, b) } else { (b, a) };
         let process = |a: Ty<'tcx>, b: Ty<'tcx>, a_is_expected| match *a.kind() {
-            ty::Opaque(ty::AliasTy { def_id, substs }) if def_id.is_local() => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) if def_id.is_local() => {
                 let def_id = def_id.expect_local();
                 let origin = match self.defining_use_anchor {
                     DefiningAnchor::Bind(_) => {
@@ -149,7 +149,9 @@ impl<'tcx> InferCtxt<'tcx> {
                     DefiningAnchor::Bubble => self.opaque_ty_origin_unchecked(def_id, cause.span),
                     DefiningAnchor::Error => return None,
                 };
-                if let ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: _ }) = *b.kind() {
+                if let ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: _ }) =
+                    *b.kind()
+                {
                     // We could accept this, but there are various ways to handle this situation, and we don't
                     // want to make a decision on it right now. Likely this case is so super rare anyway, that
                     // no one encounters it in practice.
@@ -478,7 +480,7 @@ where
                 substs.as_generator().resume_ty().visit_with(self);
             }
 
-            ty::Opaque(ty::AliasTy { def_id, ref substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, ref substs }) => {
                 // Skip lifetime paramters that are not captures.
                 let variances = self.tcx.variances_of(*def_id);
 
@@ -489,7 +491,7 @@ where
                 }
             }
 
-            ty::Projection(proj)
+            ty::Alias(ty::Projection, proj)
                 if self.tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder =>
             {
                 // Skip lifetime paramters that are not captures.
@@ -566,7 +568,7 @@ impl<'tcx> InferCtxt<'tcx> {
                     // We can't normalize associated types from `rustc_infer`,
                     // but we can eagerly register inference variables for them.
                     // FIXME(RPITIT): Don't replace RPITITs with inference vars.
-                    ty::Projection(projection_ty)
+                    ty::Alias(ty::Projection, projection_ty)
                         if !projection_ty.has_escaping_bound_vars()
                             && tcx.def_kind(projection_ty.def_id)
                                 != DefKind::ImplTraitPlaceholder =>
@@ -581,13 +583,13 @@ impl<'tcx> InferCtxt<'tcx> {
                     }
                     // Replace all other mentions of the same opaque type with the hidden type,
                     // as the bounds must hold on the hidden type after all.
-                    ty::Opaque(ty::AliasTy { def_id: def_id2, substs: substs2 })
+                    ty::Alias(ty::Opaque, ty::AliasTy { def_id: def_id2, substs: substs2 })
                         if def_id.to_def_id() == def_id2 && substs == substs2 =>
                     {
                         hidden_ty
                     }
                     // FIXME(RPITIT): This can go away when we move to associated types
-                    ty::Projection(proj)
+                    ty::Alias(ty::Projection, proj)
                         if def_id.to_def_id() == proj.def_id && substs == proj.substs =>
                     {
                         hidden_ty

compiler/rustc_infer/src/infer/outlives/components.rs

@@ -130,7 +130,7 @@ fn compute_components<'tcx>(
             // outlives any other lifetime, which is unsound.
             // See https://github.com/rust-lang/rust/issues/84305 for
             // more details.
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 out.push(Component::Opaque(def_id, substs));
             },
 
@@ -142,7 +142,7 @@ fn compute_components<'tcx>(
             // trait-ref. Therefore, if we see any higher-ranked regions,
             // we simply fallback to the most restrictive rule, which
             // requires that `Pi: 'a` for all `i`.
-            ty::Projection(ref data) => {
+            ty::Alias(ty::Projection, ref data) => {
                 if !data.has_escaping_bound_vars() {
                     // best case: no escaping regions, so push the
                     // projection and skip the subtree (thus generating no

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -338,7 +338,7 @@ where
             substs,
             true,
             |ty| match *ty.kind() {
-                ty::Opaque(ty::AliasTy { def_id, substs }) => (def_id, substs),
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => (def_id, substs),
                 _ => bug!("expected only projection types from env, not {:?}", ty),
             },
         );
@@ -359,7 +359,9 @@ where
             projection_ty.substs,
             false,
             |ty| match ty.kind() {
-                ty::Projection(projection_ty) => (projection_ty.def_id, projection_ty.substs),
+                ty::Alias(ty::Projection, projection_ty) => {
+                    (projection_ty.def_id, projection_ty.substs)
+                }
                 _ => bug!("expected only projection types from env, not {:?}", ty),
             },
         );

compiler/rustc_infer/src/infer/sub.rs

@@ -131,14 +131,14 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
             }
 
             (
-                &ty::Opaque(ty::AliasTy { def_id: a_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: _ }),
-                &ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: _ }),
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: _ }),
             ) if a_def_id == b_def_id => {
                 self.fields.infcx.super_combine_tys(self, a, b)?;
                 Ok(a)
             }
-            (&ty::Opaque(ty::AliasTy { def_id, substs: _ }), _)
+            (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }), _)
-            | (_, &ty::Opaque(ty::AliasTy { def_id, substs: _ }))
+            | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }))
                 if self.fields.define_opaque_types && def_id.is_local() =>
             {
                 self.fields.obligations.extend(

compiler/rustc_lint/src/builtin.rs

@@ -3016,8 +3016,8 @@ impl ClashingExternDeclarations {
                         | (Closure(..), Closure(..))
                         | (Generator(..), Generator(..))
                         | (GeneratorWitness(..), GeneratorWitness(..))
-                        | (Projection(..), Projection(..))
+                        | (Alias(ty::Projection, ..), Alias(ty::Projection, ..))
-                        | (Opaque(..), Opaque(..)) => false,
+                        | (Alias(ty::Opaque, ..), Alias(ty::Opaque, ..)) => false,
 
                         // These definitely should have been caught above.
                         (Bool, Bool) | (Char, Char) | (Never, Never) | (Str, Str) => unreachable!(),

compiler/rustc_lint/src/opaque_hidden_inferred_bound.rs

@@ -117,7 +117,7 @@ impl<'tcx> LateLintPass<'tcx> for OpaqueHiddenInferredBound {
                     // then we can emit a suggestion to add the bound.
                     let add_bound = match (proj_term.kind(), assoc_pred.kind().skip_binder()) {
                         (
-                            ty::Opaque(ty::AliasTy { def_id, substs: _ }),
+                            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }),
                             ty::PredicateKind::Clause(ty::Clause::Trait(trait_pred)),
                         ) => Some(AddBound {
                             suggest_span: cx.tcx.def_span(*def_id).shrink_to_hi(),

compiler/rustc_lint/src/types.rs

@@ -1139,18 +1139,20 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
 
             // While opaque types are checked for earlier, if a projection in a struct field
             // normalizes to an opaque type, then it will reach this branch.
-            ty::Opaque(..) => {
+            ty::Alias(ty::Opaque, ..) => {
                 FfiUnsafe { ty, reason: fluent::lint_improper_ctypes_opaque, help: None }
             }
 
             // `extern "C" fn` functions can have type parameters, which may or may not be FFI-safe,
             //  so they are currently ignored for the purposes of this lint.
-            ty::Param(..) | ty::Projection(..) if matches!(self.mode, CItemKind::Definition) => {
+            ty::Param(..) | ty::Alias(ty::Projection, ..)
+                if matches!(self.mode, CItemKind::Definition) =>
+            {
                 FfiSafe
             }
 
             ty::Param(..)
-            | ty::Projection(..)
+            | ty::Alias(ty::Projection, ..)
             | ty::Infer(..)
             | ty::Bound(..)
             | ty::Error(_)
@@ -1205,7 +1207,7 @@ impl<'a, 'tcx> ImproperCTypesVisitor<'a, 'tcx> {
                     return ControlFlow::CONTINUE;
                 }
 
-                if let ty::Opaque(..) = ty.kind() {
+                if let ty::Alias(ty::Opaque, ..) = ty.kind() {
                     ControlFlow::Break(ty)
                 } else {
                     ty.super_visit_with(self)

compiler/rustc_lint/src/unused.rs

@@ -96,7 +96,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
 
         if let hir::ExprKind::Match(await_expr, _arms, hir::MatchSource::AwaitDesugar) = expr.kind
             && let ty = cx.typeck_results().expr_ty(&await_expr)
-            && let ty::Opaque(ty::AliasTy { def_id: future_def_id, substs: _ }) = ty.kind()
+            && let ty::Alias(ty::Opaque, ty::AliasTy { def_id: future_def_id, substs: _ }) = ty.kind()
             && cx.tcx.ty_is_opaque_future(ty)
             // FIXME: This also includes non-async fns that return `impl Future`.
             && let async_fn_def_id = cx.tcx.parent(*future_def_id)
@@ -251,7 +251,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                         .map(|inner| MustUsePath::Boxed(Box::new(inner)))
                 }
                 ty::Adt(def, _) => is_def_must_use(cx, def.did(), span),
-                ty::Opaque(ty::AliasTy { def_id: def, substs: _ }) => {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id: def, substs: _ }) => {
                     elaborate_predicates_with_span(
                         cx.tcx,
                         cx.tcx.explicit_item_bounds(def).iter().cloned(),

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1111,7 +1111,7 @@ fn should_encode_trait_impl_trait_tys<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) ->
     // associated types.
     tcx.fn_sig(trait_item_def_id).skip_binder().output().walk().any(|arg| {
         if let ty::GenericArgKind::Type(ty) = arg.unpack()
-            && let ty::Projection(data) = ty.kind()
+            && let ty::Alias(ty::Projection, data) = ty.kind()
             && tcx.def_kind(data.def_id) == DefKind::ImplTraitPlaceholder
         {
             true

compiler/rustc_middle/src/ty/context.rs

@@ -115,8 +115,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type ListBinderExistentialPredicate = &'tcx List<PolyExistentialPredicate<'tcx>>;
     type BinderListTy = Binder<'tcx, &'tcx List<Ty<'tcx>>>;
     type ListTy = &'tcx List<Ty<'tcx>>;
-    type ProjectionTy = ty::AliasTy<'tcx>;
+    type AliasTy = ty::AliasTy<'tcx>;
-    type OpaqueTy = ty::AliasTy<'tcx>;
     type ParamTy = ParamTy;
     type BoundTy = ty::BoundTy;
     type PlaceholderType = ty::PlaceholderType;
@@ -2145,8 +2144,7 @@ impl<'tcx> TyCtxt<'tcx> {
                     Bound,
                     Param,
                     Infer,
-                    Projection,
+                    Alias,
-                    Opaque,
                     Foreign
                 )?;
 
@@ -2323,7 +2321,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Given a `ty`, return whether it's an `impl Future<...>`.
     pub fn ty_is_opaque_future(self, ty: Ty<'_>) -> bool {
-        let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = ty.kind() else { return false };
+        let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = ty.kind() else { return false };
         let future_trait = self.require_lang_item(LangItem::Future, None);
 
         self.explicit_item_bounds(def_id).iter().any(|(predicate, _)| {
@@ -2598,7 +2596,7 @@ impl<'tcx> TyCtxt<'tcx> {
             substs.len(),
             "wrong number of generic parameters for {item_def_id:?}: {substs:?}",
         );
-        self.mk_ty(Projection(AliasTy { def_id: item_def_id, substs }))
+        self.mk_ty(Alias(ty::Projection, AliasTy { def_id: item_def_id, substs }))
     }
 
     #[inline]
@@ -2668,7 +2666,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_opaque(self, def_id: DefId, substs: SubstsRef<'tcx>) -> Ty<'tcx> {
-        self.mk_ty(Opaque(ty::AliasTy { def_id, substs }))
+        self.mk_ty(Alias(ty::Opaque, ty::AliasTy { def_id, substs }))
     }
 
     pub fn mk_place_field(self, place: Place<'tcx>, f: Field, ty: Ty<'tcx>) -> Place<'tcx> {

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -4,7 +4,7 @@ use std::ops::ControlFlow;
 
 use crate::ty::{
     visit::TypeVisitable, AliasTy, Const, ConstKind, DefIdTree, ExistentialPredicate, InferConst,
-    InferTy, PolyTraitPredicate, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
+    InferTy, Opaque, PolyTraitPredicate, Ty, TyCtxt, TypeSuperVisitable, TypeVisitor,
 };
 
 use rustc_data_structures::fx::FxHashMap;
@@ -457,10 +457,10 @@ impl<'tcx> TypeVisitor<'tcx> for IsSuggestableVisitor<'tcx> {
                 return ControlFlow::Break(());
             }
 
-            Opaque(AliasTy { def_id, substs: _ }) => {
+            Alias(Opaque, AliasTy { def_id, substs: _ }) => {
                 let parent = self.tcx.parent(*def_id);
                 if let hir::def::DefKind::TyAlias | hir::def::DefKind::AssocTy = self.tcx.def_kind(parent)
-                    && let Opaque(AliasTy { def_id: parent_opaque_def_id, substs: _ }) = self.tcx.type_of(parent).kind()
+                    && let Alias(Opaque, AliasTy { def_id: parent_opaque_def_id, substs: _ }) = self.tcx.type_of(parent).kind()
                     && parent_opaque_def_id == def_id
                 {
                     // Okay

compiler/rustc_middle/src/ty/error.rs

@@ -337,9 +337,9 @@ impl<'tcx> Ty<'tcx> {
             ty::Infer(ty::FreshTy(_)) => "fresh type".into(),
             ty::Infer(ty::FreshIntTy(_)) => "fresh integral type".into(),
             ty::Infer(ty::FreshFloatTy(_)) => "fresh floating-point type".into(),
-            ty::Projection(_) => "associated type".into(),
+            ty::Alias(ty::Projection, _) => "associated type".into(),
             ty::Param(p) => format!("type parameter `{}`", p).into(),
-            ty::Opaque(..) => "opaque type".into(),
+            ty::Alias(ty::Opaque, ..) => "opaque type".into(),
             ty::Error(_) => "type error".into(),
         }
     }
@@ -375,9 +375,9 @@ impl<'tcx> Ty<'tcx> {
             ty::Tuple(..) => "tuple".into(),
             ty::Placeholder(..) => "higher-ranked type".into(),
             ty::Bound(..) => "bound type variable".into(),
-            ty::Projection(_) => "associated type".into(),
+            ty::Alias(ty::Projection, _) => "associated type".into(),
             ty::Param(_) => "type parameter".into(),
-            ty::Opaque(..) => "opaque type".into(),
+            ty::Alias(ty::Opaque, ..) => "opaque type".into(),
         }
     }
 }
@@ -400,7 +400,7 @@ impl<'tcx> TyCtxt<'tcx> {
                         diag.note("no two closures, even if identical, have the same type");
                         diag.help("consider boxing your closure and/or using it as a trait object");
                     }
-                    (ty::Opaque(..), ty::Opaque(..)) => {
+                    (ty::Alias(ty::Opaque, ..), ty::Alias(ty::Opaque, ..)) => {
                         // Issue #63167
                         diag.note("distinct uses of `impl Trait` result in different opaque types");
                     }
@@ -439,10 +439,10 @@ impl<'tcx> TyCtxt<'tcx> {
                              #traits-as-parameters",
                         );
                     }
-                    (ty::Projection(_), ty::Projection(_)) => {
+                    (ty::Alias(ty::Projection, _), ty::Alias(ty::Projection, _)) => {
                         diag.note("an associated type was expected, but a different one was found");
                     }
-                    (ty::Param(p), ty::Projection(proj)) | (ty::Projection(proj), ty::Param(p))
+                    (ty::Param(p), ty::Alias(ty::Projection, proj)) | (ty::Alias(ty::Projection, proj), ty::Param(p))
                         if self.def_kind(proj.def_id) != DefKind::ImplTraitPlaceholder =>
                     {
                         let generics = self.generics_of(body_owner_def_id);
@@ -493,8 +493,8 @@ impl<'tcx> TyCtxt<'tcx> {
                             diag.note("you might be missing a type parameter or trait bound");
                         }
                     }
-                    (ty::Param(p), ty::Dynamic(..) | ty::Opaque(..))
+                    (ty::Param(p), ty::Dynamic(..) | ty::Alias(ty::Opaque, ..))
-                    | (ty::Dynamic(..) | ty::Opaque(..), ty::Param(p)) => {
+                    | (ty::Dynamic(..) | ty::Alias(ty::Opaque, ..), ty::Param(p)) => {
                         let generics = self.generics_of(body_owner_def_id);
                         let p_span = self.def_span(generics.type_param(p, self).def_id);
                         if !sp.contains(p_span) {
@@ -553,7 +553,7 @@ impl<T> Trait<T> for X {
                             diag.span_label(p_span, "this type parameter");
                         }
                     }
-                    (ty::Projection(proj_ty), _) if self.def_kind(proj_ty.def_id) != DefKind::ImplTraitPlaceholder => {
+                    (ty::Alias(ty::Projection, proj_ty), _) if self.def_kind(proj_ty.def_id) != DefKind::ImplTraitPlaceholder => {
                         self.expected_projection(
                             diag,
                             proj_ty,
@@ -562,7 +562,7 @@ impl<T> Trait<T> for X {
                             cause.code(),
                         );
                     }
-                    (_, ty::Projection(proj_ty)) if self.def_kind(proj_ty.def_id) != DefKind::ImplTraitPlaceholder => {
+                    (_, ty::Alias(ty::Projection, proj_ty)) if self.def_kind(proj_ty.def_id) != DefKind::ImplTraitPlaceholder => {
                         let msg = format!(
                             "consider constraining the associated type `{}` to `{}`",
                             values.found, values.expected,
@@ -779,7 +779,8 @@ fn foo(&self) -> Self::T { String::new() }
         ty: Ty<'tcx>,
     ) -> bool {
         let assoc = self.associated_item(proj_ty.def_id);
-        if let ty::Opaque(ty::AliasTy { def_id, substs: _ }) = *proj_ty.self_ty().kind() {
+        if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) = *proj_ty.self_ty().kind()
+        {
             let opaque_local_def_id = def_id.as_local();
             let opaque_hir_ty = if let Some(opaque_local_def_id) = opaque_local_def_id {
                 match &self.hir().expect_item(opaque_local_def_id).kind {
@@ -828,7 +829,7 @@ fn foo(&self) -> Self::T { String::new() }
             .filter_map(|(_, item)| {
                 let method = self.fn_sig(item.def_id);
                 match *method.output().skip_binder().kind() {
-                    ty::Projection(ty::AliasTy { def_id: item_def_id, .. })
+                    ty::Alias(ty::Projection, ty::AliasTy { def_id: item_def_id, .. })
                         if item_def_id == proj_ty_item_def_id =>
                     {
                         Some((

compiler/rustc_middle/src/ty/fast_reject.rs

@@ -126,7 +126,7 @@ pub fn simplify_type<'tcx>(
             TreatParams::AsPlaceholder => Some(PlaceholderSimplifiedType),
             TreatParams::AsInfer => None,
         },
-        ty::Opaque(..) | ty::Projection(_) => match treat_params {
+        ty::Alias(ty::Opaque, ..) | ty::Alias(ty::Projection, _) => match treat_params {
             // When treating `ty::Param` as a placeholder, projections also
             // don't unify with anything else as long as they are fully normalized.
             //
@@ -225,7 +225,10 @@ impl DeepRejectCtxt {
         match impl_ty.kind() {
             // Start by checking whether the type in the impl may unify with
             // pretty much everything. Just return `true` in that case.
-            ty::Param(_) | ty::Projection(_) | ty::Error(_) | ty::Opaque(..) => return true,
+            ty::Param(_)
+            | ty::Alias(ty::Projection, _)
+            | ty::Error(_)
+            | ty::Alias(ty::Opaque, ..) => return true,
             // These types only unify with inference variables or their own
             // variant.
             ty::Bool
@@ -323,7 +326,7 @@ impl DeepRejectCtxt {
                 _ => false,
             },
 
-            ty::Opaque(..) => true,
+            ty::Alias(ty::Opaque, ..) => true,
 
             // Impls cannot contain these types as these cannot be named directly.
             ty::FnDef(..) | ty::Closure(..) | ty::Generator(..) => false,
@@ -344,7 +347,7 @@ impl DeepRejectCtxt {
             // projections can unify with other stuff.
             //
             // Looking forward to lazy normalization this is the safer strategy anyways.
-            ty::Projection(_) => true,
+            ty::Alias(ty::Projection, _) => true,
 
             ty::Error(_) => true,
 

compiler/rustc_middle/src/ty/flags.rs

@@ -155,12 +155,12 @@ impl FlagComputation {
                 self.add_substs(substs);
             }
 
-            &ty::Projection(data) => {
+            &ty::Alias(ty::Projection, data) => {
                 self.add_flags(TypeFlags::HAS_TY_PROJECTION);
                 self.add_projection_ty(data);
             }
 
-            &ty::Opaque(ty::AliasTy { def_id: _, substs }) => {
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs }) => {
                 self.add_flags(TypeFlags::HAS_TY_OPAQUE);
                 self.add_substs(substs);
             }

compiler/rustc_middle/src/ty/inhabitedness/mod.rs

@@ -112,7 +112,7 @@ impl<'tcx> Ty<'tcx> {
                 InhabitedPredicate::True
             }
             Never => InhabitedPredicate::False,
-            Param(_) | Projection(_) => InhabitedPredicate::GenericType(self),
+            Param(_) | Alias(ty::Projection, _) => InhabitedPredicate::GenericType(self),
             Tuple(tys) if tys.is_empty() => InhabitedPredicate::True,
             // use a query for more complex cases
             Adt(..) | Array(..) | Tuple(_) => tcx.inhabited_predicate_type(self),

compiler/rustc_middle/src/ty/layout.rs

@@ -271,7 +271,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
                 let non_zero = !ty.is_unsafe_ptr();
                 let tail = tcx.struct_tail_erasing_lifetimes(pointee, param_env);
                 match tail.kind() {
-                    ty::Param(_) | ty::Projection(_) => {
+                    ty::Param(_) | ty::Alias(ty::Projection, _) => {
                         debug_assert!(tail.has_non_region_param());
                         Ok(SizeSkeleton::Pointer { non_zero, tail: tcx.erase_regions(tail) })
                     }
@@ -349,7 +349,7 @@ impl<'tcx> SizeSkeleton<'tcx> {
                 }
             }
 
-            ty::Projection(_) | ty::Opaque(..) => {
+            ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..) => {
                 let normalized = tcx.normalize_erasing_regions(param_env, ty);
                 if ty == normalized {
                     Err(err)
@@ -757,10 +757,10 @@ where
                     }
                 }
 
-                ty::Projection(_)
+                ty::Alias(ty::Projection, _)
                 | ty::Bound(..)
                 | ty::Placeholder(..)
-                | ty::Opaque(..)
+                | ty::Alias(ty::Opaque, ..)
                 | ty::Param(_)
                 | ty::Infer(_)
                 | ty::Error(_) => bug!("TyAndLayout::field: unexpected type `{}`", this.ty),

compiler/rustc_middle/src/ty/mod.rs

@@ -64,6 +64,7 @@ use std::ops::ControlFlow;
 use std::{fmt, str};
 
 pub use crate::ty::diagnostics::*;
+pub use rustc_type_ir::AliasKind::*;
 pub use rustc_type_ir::DynKind::*;
 pub use rustc_type_ir::InferTy::*;
 pub use rustc_type_ir::RegionKind::*;

compiler/rustc_middle/src/ty/print/mod.rs

@@ -275,10 +275,10 @@ fn characteristic_def_id_of_type_cached<'a>(
         | ty::Uint(_)
         | ty::Str
         | ty::FnPtr(_)
-        | ty::Projection(_)
+        | ty::Alias(ty::Projection, _)
         | ty::Placeholder(..)
         | ty::Param(_)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Infer(_)
         | ty::Bound(..)
         | ty::Error(_)

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -718,7 +718,7 @@ pub trait PrettyPrinter<'tcx>:
             ty::Foreign(def_id) => {
                 p!(print_def_path(def_id, &[]));
             }
-            ty::Projection(ref data) => {
+            ty::Alias(ty::Projection, ref data) => {
                 if !(self.should_print_verbose() || NO_QUERIES.with(|q| q.get()))
                     && self.tcx().def_kind(data.def_id) == DefKind::ImplTraitPlaceholder
                 {
@@ -728,7 +728,7 @@ pub trait PrettyPrinter<'tcx>:
                 }
             }
             ty::Placeholder(placeholder) => p!(write("Placeholder({:?})", placeholder)),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 // FIXME(eddyb) print this with `print_def_path`.
                 // We use verbose printing in 'NO_QUERIES' mode, to
                 // avoid needing to call `predicates_of`. This should
@@ -743,7 +743,7 @@ pub trait PrettyPrinter<'tcx>:
                 let parent = self.tcx().parent(def_id);
                 match self.tcx().def_kind(parent) {
                     DefKind::TyAlias | DefKind::AssocTy => {
-                        if let ty::Opaque(ty::AliasTy { def_id: d, substs: _ }) =
+                        if let ty::Alias(ty::Opaque, ty::AliasTy { def_id: d, substs: _ }) =
                             *self.tcx().type_of(parent).kind()
                         {
                             if d == def_id {
@@ -1021,7 +1021,7 @@ pub trait PrettyPrinter<'tcx>:
                         // Skip printing `<[generator@] as Generator<_>>::Return` from async blocks,
                         // unless we can find out what generator return type it comes from.
                         let term = if let Some(ty) = term.skip_binder().ty()
-                            && let ty::Projection(proj) = ty.kind()
+                            && let ty::Alias(ty::Projection, proj) = ty.kind()
                             && let Some(assoc) = tcx.opt_associated_item(proj.def_id)
                             && assoc.trait_container(tcx) == tcx.lang_items().gen_trait()
                             && assoc.name == rustc_span::sym::Return

compiler/rustc_middle/src/ty/relate.rs

@@ -551,14 +551,14 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
         }
 
         // these two are already handled downstream in case of lazy normalization
-        (&ty::Projection(a_data), &ty::Projection(b_data)) => {
+        (&ty::Alias(ty::Projection, a_data), &ty::Alias(ty::Projection, b_data)) => {
             let projection_ty = relation.relate(a_data, b_data)?;
             Ok(tcx.mk_projection(projection_ty.def_id, projection_ty.substs))
         }
 
         (
-            &ty::Opaque(ty::AliasTy { def_id: a_def_id, substs: a_substs }),
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, substs: a_substs }),
-            &ty::Opaque(ty::AliasTy { def_id: b_def_id, substs: b_substs }),
+            &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, substs: b_substs }),
         ) if a_def_id == b_def_id => {
             if relation.intercrate() {
                 // During coherence, opaque types should be treated as equal to each other, even if their generic params

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -651,9 +651,11 @@ impl<'tcx> TypeSuperFoldable<'tcx> for Ty<'tcx> {
             }
             ty::GeneratorWitness(types) => ty::GeneratorWitness(types.try_fold_with(folder)?),
             ty::Closure(did, substs) => ty::Closure(did, substs.try_fold_with(folder)?),
-            ty::Projection(data) => ty::Projection(data.try_fold_with(folder)?),
+            ty::Alias(ty::Projection, data) => {
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+                ty::Alias(ty::Projection, data.try_fold_with(folder)?)
-                ty::Opaque(ty::AliasTy { def_id, substs: substs.try_fold_with(folder)? })
+            }
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: substs.try_fold_with(folder)? })
             }
 
             ty::Bool
@@ -699,8 +701,10 @@ impl<'tcx> TypeSuperVisitable<'tcx> for Ty<'tcx> {
             ty::Generator(_did, ref substs, _) => substs.visit_with(visitor),
             ty::GeneratorWitness(ref types) => types.visit_with(visitor),
             ty::Closure(_did, ref substs) => substs.visit_with(visitor),
-            ty::Projection(ref data) => data.visit_with(visitor),
+            ty::Alias(ty::Projection, ref data) => data.visit_with(visitor),
-            ty::Opaque(ty::AliasTy { def_id: _, ref substs }) => substs.visit_with(visitor),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, ref substs }) => {
+                substs.visit_with(visitor)
+            }
 
             ty::Bool
             | ty::Char

compiler/rustc_middle/src/ty/sty.rs

@@ -1980,7 +1980,7 @@ impl<'tcx> Ty<'tcx> {
 
     #[inline]
     pub fn is_impl_trait(self) -> bool {
-        matches!(self.kind(), Opaque(..))
+        matches!(self.kind(), Alias(ty::Opaque, ..))
     }
 
     #[inline]
@@ -2047,7 +2047,10 @@ impl<'tcx> Ty<'tcx> {
             ty::Adt(adt, _) if adt.is_enum() => adt.repr().discr_type().to_ty(tcx),
             ty::Generator(_, substs, _) => substs.as_generator().discr_ty(tcx),
 
-            ty::Param(_) | ty::Projection(_) | ty::Opaque(..) | ty::Infer(ty::TyVar(_)) => {
+            ty::Param(_)
+            | ty::Alias(ty::Projection, _)
+            | ty::Alias(ty::Opaque, ..)
+            | ty::Infer(ty::TyVar(_)) => {
                 let assoc_items = tcx.associated_item_def_ids(
                     tcx.require_lang_item(hir::LangItem::DiscriminantKind, None),
                 );
@@ -2127,7 +2130,7 @@ impl<'tcx> Ty<'tcx> {
 
             // type parameters only have unit metadata if they're sized, so return true
             // to make sure we double check this during confirmation
-            ty::Param(_) |  ty::Projection(_) | ty::Opaque(..) => (tcx.types.unit, true),
+            ty::Param(_) |  ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..) => (tcx.types.unit, true),
 
             ty::Infer(ty::TyVar(_))
             | ty::Bound(..)
@@ -2203,7 +2206,7 @@ impl<'tcx> Ty<'tcx> {
 
             ty::Adt(def, _substs) => def.sized_constraint(tcx).0.is_empty(),
 
-            ty::Projection(_) | ty::Param(_) | ty::Opaque(..) => false,
+            ty::Alias(ty::Projection, _) | ty::Param(_) | ty::Alias(ty::Opaque, ..) => false,
 
             ty::Infer(ty::TyVar(_)) => false,
 
@@ -2259,9 +2262,9 @@ impl<'tcx> Ty<'tcx> {
             ty::Generator(..) | ty::GeneratorWitness(..) => false,
 
             // Might be, but not "trivial" so just giving the safe answer.
-            ty::Adt(..) | ty::Closure(..) | ty::Opaque(..) => false,
+            ty::Adt(..) | ty::Closure(..) | ty::Alias(ty::Opaque, ..) => false,
 
-            ty::Projection(..) | ty::Param(..) | ty::Infer(..) | ty::Error(..) => false,
+            ty::Alias(ty::Projection, ..) | ty::Param(..) | ty::Infer(..) | ty::Error(..) => false,
 
             ty::Bound(..) | ty::Placeholder(..) => {
                 bug!("`is_trivially_pure_clone_copy` applied to unexpected type: {:?}", self);

compiler/rustc_middle/src/ty/util.rs

@@ -259,7 +259,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
                 ty::Tuple(_) => break,
 
-                ty::Projection(_) | ty::Opaque(..) => {
+                ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..) => {
                     let normalized = normalize(ty);
                     if ty == normalized {
                         return ty;
@@ -332,8 +332,8 @@ impl<'tcx> TyCtxt<'tcx> {
                         break;
                     }
                 }
-                (ty::Projection(_) | ty::Opaque(..), _)
+                (ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..), _)
-                | (_, ty::Projection(_) | ty::Opaque(..)) => {
+                | (_, ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..)) => {
                     // If either side is a projection, attempt to
                     // progress via normalization. (Should be safe to
                     // apply to both sides as normalization is
@@ -826,7 +826,7 @@ impl<'tcx> TypeFolder<'tcx> for OpaqueTypeExpander<'tcx> {
     }
 
     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
-        if let ty::Opaque(ty::AliasTy { def_id, substs }) = *t.kind() {
+        if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) = *t.kind() {
             self.expand_opaque_ty(def_id, substs).unwrap_or(t)
         } else if t.has_opaque_types() {
             t.super_fold_with(self)
@@ -938,10 +938,10 @@ impl<'tcx> Ty<'tcx> {
             | ty::Generator(..)
             | ty::GeneratorWitness(_)
             | ty::Infer(_)
-            | ty::Opaque(..)
+            | ty::Alias(ty::Opaque, ..)
             | ty::Param(_)
             | ty::Placeholder(_)
-            | ty::Projection(_) => false,
+            | ty::Alias(ty::Projection, _) => false,
         }
     }
 
@@ -978,10 +978,10 @@ impl<'tcx> Ty<'tcx> {
             | ty::Generator(..)
             | ty::GeneratorWitness(_)
             | ty::Infer(_)
-            | ty::Opaque(..)
+            | ty::Alias(ty::Opaque, ..)
             | ty::Param(_)
             | ty::Placeholder(_)
-            | ty::Projection(_) => false,
+            | ty::Alias(ty::Projection, _) => false,
         }
     }
 
@@ -1101,8 +1101,8 @@ impl<'tcx> Ty<'tcx> {
             //
             // FIXME(ecstaticmorse): Maybe we should `bug` here? This should probably only be
             // called for known, fully-monomorphized types.
-            ty::Projection(_)
+            ty::Alias(ty::Projection, _)
-            | ty::Opaque(..)
+            | ty::Alias(ty::Opaque, ..)
             | ty::Param(_)
             | ty::Bound(..)
             | ty::Placeholder(_)
@@ -1237,11 +1237,11 @@ pub fn needs_drop_components<'tcx>(
 
         // These require checking for `Copy` bounds or `Adt` destructors.
         ty::Adt(..)
-        | ty::Projection(..)
+        | ty::Alias(ty::Projection, ..)
         | ty::Param(_)
         | ty::Bound(..)
         | ty::Placeholder(..)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Infer(_)
         | ty::Closure(..)
         | ty::Generator(..) => Ok(smallvec![ty]),
@@ -1265,13 +1265,13 @@ pub fn is_trivially_const_drop<'tcx>(ty: Ty<'tcx>) -> bool {
         | ty::Never
         | ty::Foreign(_) => true,
 
-        ty::Opaque(..)
+        ty::Alias(ty::Opaque, ..)
         | ty::Dynamic(..)
         | ty::Error(_)
         | ty::Bound(..)
         | ty::Param(_)
         | ty::Placeholder(_)
-        | ty::Projection(_)
+        | ty::Alias(ty::Projection, _)
         | ty::Infer(_) => false,
 
         // Not trivial because they have components, and instead of looking inside,

compiler/rustc_middle/src/ty/visit.rs

@@ -654,7 +654,7 @@ impl<'tcx> TypeVisitor<'tcx> for LateBoundRegionsCollector {
         // ignore the inputs to a projection, as they may not appear
         // in the normalized form
         if self.just_constrained {
-            if let ty::Projection(..) | ty::Opaque(..) = t.kind() {
+            if let ty::Alias(ty::Projection, ..) | ty::Alias(ty::Opaque, ..) = t.kind() {
                 return ControlFlow::CONTINUE;
             }
         }

compiler/rustc_middle/src/ty/walk.rs

@@ -165,7 +165,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 stack.push(ty.into());
                 stack.push(lt.into());
             }
-            ty::Projection(data) => {
+            ty::Alias(ty::Projection, data) => {
                 stack.extend(data.substs.iter().rev());
             }
             ty::Dynamic(obj, lt, _) => {
@@ -188,7 +188,7 @@ fn push_inner<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent: GenericArg<'tcx>)
                 }));
             }
             ty::Adt(_, substs)
-            | ty::Opaque(ty::AliasTy { def_id: _, substs })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs })
             | ty::Closure(_, substs)
             | ty::Generator(_, substs, _)
             | ty::FnDef(_, substs) => {

compiler/rustc_mir_build/src/build/block.rs

@@ -373,7 +373,9 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // the case of `!`, no return value is required, as the block will never return.
             // Opaque types of empty bodies also need this unit assignment, in order to infer that their
             // type is actually unit. Otherwise there will be no defining use found in the MIR.
-            if destination_ty.is_unit() || matches!(destination_ty.kind(), ty::Opaque(..)) {
+            if destination_ty.is_unit()
+                || matches!(destination_ty.kind(), ty::Alias(ty::Opaque, ..))
+            {
                 // We only want to assign an implicit `()` as the return value of the block if the
                 // block does not diverge. (Otherwise, we may try to assign a unit to a `!`-type.)
                 this.cfg.push_assign_unit(block, source_info, destination, this.tcx);

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -121,7 +121,7 @@ impl<'tcx> ConstToPat<'tcx> {
                 ty::Dynamic(..) => {
                     "trait objects cannot be used in patterns".to_string()
                 }
-                ty::Opaque(..) => {
+                ty::Alias(ty::Opaque, ..) => {
                     "opaque types cannot be used in patterns".to_string()
                 }
                 ty::Closure(..) => {

compiler/rustc_mir_build/src/thir/pattern/usefulness.rs

@@ -845,7 +845,7 @@ fn is_useful<'p, 'tcx>(
 
         // Opaque types can't get destructured/split, but the patterns can
         // actually hint at hidden types, so we use the patterns' types instead.
-        if let ty::Opaque(..) = ty.kind() {
+        if let ty::Alias(ty::Opaque, ..) = ty.kind() {
             if let Some(row) = rows.first() {
                 ty = row.head().ty();
             }

compiler/rustc_mir_transform/src/inline.rs

@@ -849,7 +849,7 @@ impl<'tcx> Visitor<'tcx> for CostChecker<'_, 'tcx> {
             };
 
             let kind = match parent_ty.ty.kind() {
-                &ty::Opaque(ty::AliasTy { def_id, substs }) => {
+                &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                     self.tcx.bound_type_of(def_id).subst(self.tcx, substs).kind()
                 }
                 kind => kind,

compiler/rustc_mir_transform/src/remove_zsts.rs

@@ -52,7 +52,11 @@ impl<'tcx> MirPass<'tcx> for RemoveZsts {
 fn maybe_zst(ty: Ty<'_>) -> bool {
     match ty.kind() {
         // maybe ZST (could be more precise)
-        ty::Adt(..) | ty::Array(..) | ty::Closure(..) | ty::Tuple(..) | ty::Opaque(..) => true,
+        ty::Adt(..)
+        | ty::Array(..)
+        | ty::Closure(..)
+        | ty::Tuple(..)
+        | ty::Alias(ty::Opaque, ..) => true,
         // definitely ZST
         ty::FnDef(..) | ty::Never => true,
         // unreachable or can't be ZST

compiler/rustc_privacy/src/lib.rs

@@ -208,7 +208,7 @@ where
                     }
                 }
             }
-            ty::Projection(proj) => {
+            ty::Alias(ty::Projection, proj) => {
                 if self.def_id_visitor.skip_assoc_tys() {
                     // Visitors searching for minimal visibility/reachability want to
                     // conservatively approximate associated types like `<Type as Trait>::Alias`
@@ -235,7 +235,7 @@ where
                     self.def_id_visitor.visit_def_id(def_id, "trait", &trait_ref)?;
                 }
             }
-            ty::Opaque(ty::AliasTy { def_id, substs: _ }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) => {
                 // Skip repeated `Opaque`s to avoid infinite recursion.
                 if self.visited_opaque_tys.insert(def_id) {
                     // The intent is to treat `impl Trait1 + Trait2` identically to

compiler/rustc_symbol_mangling/src/legacy.rs

@@ -216,8 +216,8 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
         match *ty.kind() {
             // Print all nominal types as paths (unlike `pretty_print_type`).
             ty::FnDef(def_id, substs)
-            | ty::Opaque(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs })
-            | ty::Projection(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Projection, ty::AliasTy { def_id, substs })
             | ty::Closure(def_id, substs)
             | ty::Generator(def_id, substs, _) => self.print_def_path(def_id, substs),
 
@@ -287,11 +287,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolPrinter<'tcx> {
         // Similar to `pretty_path_qualified`, but for the other
         // types that are printed as paths (see `print_type` above).
         match self_ty.kind() {
-            ty::FnDef(..)
+            ty::FnDef(..) | ty::Alias(..) | ty::Closure(..) | ty::Generator(..)
-            | ty::Opaque(..)
-            | ty::Projection(_)
-            | ty::Closure(..)
-            | ty::Generator(..)
                 if trait_ref.is_none() =>
             {
                 self.print_type(self_ty)

compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -646,10 +646,10 @@ fn encode_ty<'tcx>(
         | ty::Error(..)
         | ty::GeneratorWitness(..)
         | ty::Infer(..)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Param(..)
         | ty::Placeholder(..)
-        | ty::Projection(..) => {
+        | ty::Alias(ty::Projection, ..) => {
             bug!("encode_ty: unexpected `{:?}`", ty.kind());
         }
     };
@@ -799,10 +799,10 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
         | ty::Error(..)
         | ty::GeneratorWitness(..)
         | ty::Infer(..)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Param(..)
         | ty::Placeholder(..)
-        | ty::Projection(..) => {
+        | ty::Alias(ty::Projection, ..) => {
             bug!("transform_ty: unexpected `{:?}`", ty.kind());
         }
     }

compiler/rustc_symbol_mangling/src/v0.rs

@@ -439,8 +439,8 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
             // Mangle all nominal types as paths.
             ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did: def_id, .. }, _)), substs)
             | ty::FnDef(def_id, substs)
-            | ty::Opaque(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs })
-            | ty::Projection(ty::AliasTy { def_id, substs })
+            | ty::Alias(ty::Projection, ty::AliasTy { def_id, substs })
             | ty::Closure(def_id, substs)
             | ty::Generator(def_id, substs, _) => {
                 self = self.print_def_path(def_id, substs)?;

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -579,14 +579,14 @@ impl<'tcx> AutoTraitFinder<'tcx> {
     pub fn is_of_param(&self, ty: Ty<'_>) -> bool {
         match ty.kind() {
             ty::Param(_) => true,
-            ty::Projection(p) => self.is_of_param(p.self_ty()),
+            ty::Alias(ty::Projection, p) => self.is_of_param(p.self_ty()),
             _ => false,
         }
     }
 
     fn is_self_referential_projection(&self, p: ty::PolyProjectionPredicate<'_>) -> bool {
         if let Some(ty) = p.term().skip_binder().ty() {
-            matches!(ty.kind(), ty::Projection(proj) if proj == &p.skip_binder().projection_ty)
+            matches!(ty.kind(), ty::Alias(ty::Projection, proj) if proj == &p.skip_binder().projection_ty)
         } else {
             false
         }

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -659,7 +659,7 @@ impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> {
             | ty::RawPtr(..)
             | ty::Never
             | ty::Tuple(..)
-            | ty::Projection(..) => self.found_non_local_ty(ty),
+            | ty::Alias(ty::Projection, ..) => self.found_non_local_ty(ty),
 
             ty::Param(..) => self.found_param_ty(ty),
 
@@ -704,7 +704,7 @@ impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> {
                 );
                 ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty))
             }
-            ty::Opaque(..) => {
+            ty::Alias(ty::Opaque, ..) => {
                 // This merits some explanation.
                 // Normally, opaque types are not involved when performing
                 // coherence checking, since it is illegal to directly

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

@@ -1787,8 +1787,8 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 ty::Closure(..) => Some(9),
                 ty::Tuple(..) => Some(10),
                 ty::Param(..) => Some(11),
-                ty::Projection(..) => Some(12),
+                ty::Alias(ty::Projection, ..) => Some(12),
-                ty::Opaque(..) => Some(13),
+                ty::Alias(ty::Opaque, ..) => Some(13),
                 ty::Never => Some(14),
                 ty::Adt(..) => Some(15),
                 ty::Generator(..) => Some(16),

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

@@ -495,7 +495,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         let self_ty = trait_pred.skip_binder().self_ty();
         let (param_ty, projection) = match self_ty.kind() {
             ty::Param(_) => (true, None),
-            ty::Projection(projection) => (false, Some(projection)),
+            ty::Alias(ty::Projection, projection) => (false, Some(projection)),
             _ => (false, None),
         };
 
@@ -855,7 +855,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     fn_sig.inputs().map_bound(|inputs| &inputs[1..]),
                 ))
             }
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 self.tcx.bound_item_bounds(def_id).subst(self.tcx, substs).iter().find_map(|pred| {
                     if let ty::PredicateKind::Clause(ty::Clause::Projection(proj)) = pred.kind().skip_binder()
                     && Some(proj.projection_ty.def_id) == self.tcx.lang_items().fn_once_output()
@@ -2644,7 +2644,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                                 Some(ident) => err.span_note(ident.span, &msg),
                                 None => err.note(&msg),
                             },
-                            ty::Opaque(ty::AliasTy { def_id, substs: _ }) => {
+                            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }) => {
                                 // Avoid printing the future from `core::future::identity_future`, it's not helpful
                                 if tcx.parent(*def_id) == identity_future {
                                     break 'print;
@@ -3221,7 +3221,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             let ocx = ObligationCtxt::new_in_snapshot(self.infcx);
             for diff in &type_diffs {
                 let Sorts(expected_found) = diff else { continue; };
-                let ty::Projection(proj) = expected_found.expected.kind() else { continue; };
+                let ty::Alias(ty::Projection, proj) = expected_found.expected.kind() else { continue; };
 
                 let origin =
                     TypeVariableOrigin { kind: TypeVariableOriginKind::TypeInference, span };

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -794,13 +794,13 @@ fn contains_illegal_self_type_reference<'tcx, T: TypeVisitable<'tcx>>(
                         ControlFlow::CONTINUE
                     }
                 }
-                ty::Projection(ref data)
+                ty::Alias(ty::Projection, ref data)
                     if self.tcx.def_kind(data.def_id) == DefKind::ImplTraitPlaceholder =>
                 {
                     // We'll deny these later in their own pass
                     ControlFlow::CONTINUE
                 }
-                ty::Projection(ref data) => {
+                ty::Alias(ty::Projection, ref data) => {
                     // This is a projected type `<Foo as SomeTrait>::X`.
 
                     // Compute supertraits of current trait lazily.
@@ -861,7 +861,7 @@ pub fn contains_illegal_impl_trait_in_trait<'tcx>(
     // FIXME(RPITIT): Perhaps we should use a visitor here?
     ty.skip_binder().walk().find_map(|arg| {
         if let ty::GenericArgKind::Type(ty) = arg.unpack()
-            && let ty::Projection(proj) = ty.kind()
+            && let ty::Alias(ty::Projection, proj) = ty.kind()
             && tcx.def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
         {
             Some(MethodViolationCode::ReferencesImplTraitInTrait(tcx.def_span(proj.def_id)))

compiler/rustc_trait_selection/src/traits/project.rs

@@ -496,7 +496,9 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
             // This is really important. While we *can* handle this, this has
             // severe performance implications for large opaque types with
             // late-bound regions. See `issue-88862` benchmark.
-            ty::Opaque(ty::AliasTy { def_id, substs }) if !substs.has_escaping_bound_vars() => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs })
+                if !substs.has_escaping_bound_vars() =>
+            {
                 // Only normalize `impl Trait` outside of type inference, usually in codegen.
                 match self.param_env.reveal() {
                     Reveal::UserFacing => ty.super_fold_with(self),
@@ -523,7 +525,7 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
                 }
             }
 
-            ty::Projection(data) if !data.has_escaping_bound_vars() => {
+            ty::Alias(ty::Projection, data) if !data.has_escaping_bound_vars() => {
                 // This branch is *mostly* just an optimization: when we don't
                 // have escaping bound vars, we don't need to replace them with
                 // placeholders (see branch below). *Also*, we know that we can
@@ -562,7 +564,7 @@ impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
                 normalized_ty.ty().unwrap()
             }
 
-            ty::Projection(data) => {
+            ty::Alias(ty::Projection, data) => {
                 // If there are escaping bound vars, we temporarily replace the
                 // bound vars with placeholders. Note though, that in the case
                 // that we still can't project for whatever reason (e.g. self
@@ -1375,8 +1377,10 @@ fn assemble_candidates_from_trait_def<'cx, 'tcx>(
     // Check whether the self-type is itself a projection.
     // If so, extract what we know from the trait and try to come up with a good answer.
     let bounds = match *obligation.predicate.self_ty().kind() {
-        ty::Projection(ref data) => tcx.bound_item_bounds(data.def_id).subst(tcx, data.substs),
+        ty::Alias(ty::Projection, ref data) => {
-        ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            tcx.bound_item_bounds(data.def_id).subst(tcx, data.substs)
+        }
+        ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
             tcx.bound_item_bounds(def_id).subst(tcx, substs)
         }
         ty::Infer(ty::TyVar(_)) => {
@@ -1616,8 +1620,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
                          // type parameters, opaques, and unnormalized projections have pointer
                         // metadata if they're known (e.g. by the param_env) to be sized
                         ty::Param(_)
-                        | ty::Projection(..)
+                        | ty::Alias(ty::Projection, ..)
-                        | ty::Opaque(..)
+                        | ty::Alias(ty::Opaque, ..)
                         | ty::Bound(..)
                         | ty::Placeholder(..)
                         | ty::Infer(..)
@@ -1671,7 +1675,7 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
 
                         // type parameters, opaques, and unnormalized projections have pointer
                         // metadata if they're known (e.g. by the param_env) to be sized
-                        ty::Param(_) | ty::Projection(..) | ty::Opaque(..)
+                        ty::Param(_) | ty::Alias(ty::Projection, ..) | ty::Alias(ty::Opaque, ..)
                             if selcx.infcx.predicate_must_hold_modulo_regions(
                                 &obligation.with(
                                     selcx.tcx(),
@@ -1687,8 +1691,8 @@ fn assemble_candidates_from_impls<'cx, 'tcx>(
 
                         // FIXME(compiler-errors): are Bound and Placeholder types ever known sized?
                         ty::Param(_)
-                        | ty::Projection(..)
+                        | ty::Alias(ty::Projection, ..)
-                        | ty::Opaque(..)
+                        | ty::Alias(ty::Opaque, ..)
                         | ty::Bound(..)
                         | ty::Placeholder(..)
                         | ty::Infer(..)

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -62,9 +62,9 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
 
         // The following *might* require a destructor: needs deeper inspection.
         ty::Dynamic(..)
-        | ty::Projection(..)
+        | ty::Alias(ty::Projection, ..)
         | ty::Param(_)
-        | ty::Opaque(..)
+        | ty::Alias(ty::Opaque, ..)
         | ty::Placeholder(..)
         | ty::Infer(_)
         | ty::Bound(..)

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -205,7 +205,9 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
             // This is really important. While we *can* handle this, this has
             // severe performance implications for large opaque types with
             // late-bound regions. See `issue-88862` benchmark.
-            ty::Opaque(ty::AliasTy { def_id, substs }) if !substs.has_escaping_bound_vars() => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs })
+                if !substs.has_escaping_bound_vars() =>
+            {
                 // Only normalize `impl Trait` outside of type inference, usually in codegen.
                 match self.param_env.reveal() {
                     Reveal::UserFacing => ty.try_super_fold_with(self),
@@ -242,7 +244,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 }
             }
 
-            ty::Projection(data) if !data.has_escaping_bound_vars() => {
+            ty::Alias(ty::Projection, data) if !data.has_escaping_bound_vars() => {
                 // This branch is just an optimization: when we don't have escaping bound vars,
                 // we don't need to replace them with placeholders (see branch below).
 
@@ -291,7 +293,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 }
             }
 
-            ty::Projection(data) => {
+            ty::Alias(ty::Projection, data) => {
                 // See note in `rustc_trait_selection::traits::project`
 
                 let tcx = self.infcx.tcx;

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

@@ -138,7 +138,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         // Before we go into the whole placeholder thing, just
         // quickly check if the self-type is a projection at all.
         match obligation.predicate.skip_binder().trait_ref.self_ty().kind() {
-            ty::Projection(_) | ty::Opaque(..) => {}
+            ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..) => {}
             ty::Infer(ty::TyVar(_)) => {
                 span_bug!(
                     obligation.cause.span,
@@ -394,7 +394,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     // still be provided by a manual implementation for
                     // this trait and type.
                 }
-                ty::Param(..) | ty::Projection(..) => {
+                ty::Param(..) | ty::Alias(ty::Projection, ..) => {
                     // 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
@@ -734,13 +734,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let self_ty = self.infcx.shallow_resolve(obligation.self_ty());
         match self_ty.skip_binder().kind() {
-            ty::Opaque(..)
+            ty::Alias(ty::Opaque, ..)
             | ty::Dynamic(..)
             | ty::Error(_)
             | ty::Bound(..)
             | ty::Param(_)
             | ty::Placeholder(_)
-            | ty::Projection(_) => {
+            | ty::Alias(ty::Projection, _) => {
                 // We don't know if these are `~const Destruct`, at least
                 // not structurally... so don't push a candidate.
             }
@@ -826,8 +826,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::Generator(_, _, _)
             | ty::GeneratorWitness(_)
             | ty::Never
-            | ty::Projection(_)
+            | ty::Alias(ty::Projection, _)
-            | ty::Opaque(ty::AliasTy { def_id: _, substs: _ })
+            | ty::Alias(ty::Opaque, ty::AliasTy { def_id: _, substs: _ })
             | ty::Param(_)
             | ty::Bound(_, _)
             | ty::Error(_)

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

@@ -155,8 +155,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let placeholder_self_ty = placeholder_trait_predicate.self_ty();
         let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
         let (def_id, substs) = match *placeholder_self_ty.kind() {
-            ty::Projection(proj) => (proj.def_id, proj.substs),
+            ty::Alias(ty::Projection, proj) => (proj.def_id, proj.substs),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => (def_id, substs),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => (def_id, substs),
             _ => bug!("projection candidate for unexpected type: {:?}", placeholder_self_ty),
         };
 
@@ -184,7 +184,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 .map_err(|_| Unimplemented)
         })?);
 
-        if let ty::Projection(..) = placeholder_self_ty.kind() {
+        if let ty::Alias(ty::Projection, ..) = placeholder_self_ty.kind() {
             let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs).predicates;
             debug!(?predicates, "projection predicates");
             for predicate in predicates {
@@ -1279,7 +1279,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                 // If we have a projection type, make sure to normalize it so we replace it
                 // with a fresh infer variable
-                ty::Projection(..) => {
+                ty::Alias(ty::Projection, ..) => {
                     let predicate = normalize_with_depth_to(
                         self,
                         obligation.param_env,

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

@@ -1595,8 +1595,8 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let tcx = self.infcx.tcx;
         let (def_id, substs) = match *placeholder_trait_predicate.trait_ref.self_ty().kind() {
-            ty::Projection(ref data) => (data.def_id, data.substs),
+            ty::Alias(ty::Projection, ref data) => (data.def_id, data.substs),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => (def_id, substs),
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => (def_id, substs),
             _ => {
                 span_bug!(
                     obligation.cause.span,
@@ -2067,7 +2067,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }))
             }
 
-            ty::Projection(_) | ty::Param(_) | ty::Opaque(..) => None,
+            ty::Alias(ty::Projection, _) | ty::Param(_) | ty::Alias(ty::Opaque, ..) => None,
             ty::Infer(ty::TyVar(_)) => Ambiguous,
 
             ty::Placeholder(..)
@@ -2167,7 +2167,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
             }
 
-            ty::Adt(..) | ty::Projection(..) | ty::Param(..) | ty::Opaque(..) => {
+            ty::Adt(..)
+            | ty::Alias(ty::Projection, ..)
+            | ty::Param(..)
+            | ty::Alias(ty::Opaque, ..) => {
                 // Fallback to whatever user-defined impls exist in this case.
                 None
             }
@@ -2220,7 +2223,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             | ty::Dynamic(..)
             | ty::Param(..)
             | ty::Foreign(..)
-            | ty::Projection(..)
+            | ty::Alias(ty::Projection, ..)
             | ty::Bound(..)
             | ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
                 bug!("asked to assemble constituent types of unexpected type: {:?}", t);
@@ -2260,7 +2263,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 t.rebind(def.all_fields().map(|f| f.ty(self.tcx(), substs)).collect())
             }
 
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 // We can resolve the `impl Trait` to its concrete type,
                 // which enforces a DAG between the functions requiring
                 // the auto trait bounds in question.

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -95,10 +95,10 @@ impl<'tcx> TypeVisitor<'tcx> for Search<'tcx> {
             ty::Foreign(_) => {
                 return ControlFlow::Break(ty);
             }
-            ty::Opaque(..) => {
+            ty::Alias(ty::Opaque, ..) => {
                 return ControlFlow::Break(ty);
             }
-            ty::Projection(..) => {
+            ty::Alias(ty::Projection, ..) => {
                 return ControlFlow::Break(ty);
             }
             ty::Closure(..) => {

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -234,7 +234,7 @@ fn extend_cause_with_original_assoc_item_obligation<'tcx>(
             // projection coming from another associated type. See
             // `src/test/ui/associated-types/point-at-type-on-obligation-failure.rs` and
             // `traits-assoc-type-in-supertrait-bad.rs`.
-            if let Some(ty::Projection(projection_ty)) = proj.term.ty().map(|ty| ty.kind())
+            if let Some(ty::Alias(ty::Projection, projection_ty)) = proj.term.ty().map(|ty| ty.kind())
                 && let Some(&impl_item_id) =
                     tcx.impl_item_implementor_ids(impl_def_id).get(&projection_ty.def_id)
                 && let Some(impl_item_span) = items
@@ -249,7 +249,7 @@ fn extend_cause_with_original_assoc_item_obligation<'tcx>(
             // An associated item obligation born out of the `trait` failed to be met. An example
             // can be seen in `ui/associated-types/point-at-type-on-obligation-failure-2.rs`.
             debug!("extended_cause_with_original_assoc_item_obligation trait proj {:?}", pred);
-            if let ty::Projection(ty::AliasTy { def_id, .. }) = *pred.self_ty().kind()
+            if let ty::Alias(ty::Projection, ty::AliasTy { def_id, .. }) = *pred.self_ty().kind()
                 && let Some(&impl_item_id) =
                     tcx.impl_item_implementor_ids(impl_def_id).get(&def_id)
                 && let Some(impl_item_span) = items
@@ -556,7 +556,7 @@ impl<'tcx> WfPredicates<'tcx> {
                     // Simple cases that are WF if their type args are WF.
                 }
 
-                ty::Projection(data) => {
+                ty::Alias(ty::Projection, data) => {
                     walker.skip_current_subtree(); // Subtree handled by compute_projection.
                     self.compute_projection(data);
                 }
@@ -648,7 +648,7 @@ impl<'tcx> WfPredicates<'tcx> {
                     // types appearing in the fn signature
                 }
 
-                ty::Opaque(ty::AliasTy { def_id, substs }) => {
+                ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                     // All of the requirements on type parameters
                     // have already been checked for `impl Trait` in
                     // return position. We do need to check type-alias-impl-trait though.

compiler/rustc_traits/src/chalk/db.rs

@@ -432,9 +432,10 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
                         (ast::Mutability::Not, chalk_ir::Mutability::Not) => true,
                     }
                 }
-                (&ty::Opaque(ty::AliasTy { def_id, substs: _ }), OpaqueType(opaque_ty_id, ..)) => {
+                (
-                    def_id == opaque_ty_id.0
+                    &ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs: _ }),
-                }
+                    OpaqueType(opaque_ty_id, ..),
+                ) => def_id == opaque_ty_id.0,
                 (&ty::FnDef(def_id, ..), FnDef(fn_def_id, ..)) => def_id == fn_def_id.0,
                 (&ty::Str, Str) => true,
                 (&ty::Never, Never) => true,
@@ -788,7 +789,7 @@ impl<'tcx> ty::TypeFolder<'tcx> for ReplaceOpaqueTyFolder<'tcx> {
     }
 
     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        if let ty::Opaque(ty::AliasTy { def_id, substs }) = *ty.kind() {
+        if let ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) = *ty.kind() {
             if def_id == self.opaque_ty_id.0 && substs == self.identity_substs {
                 return self.tcx.mk_ty(ty::Bound(
                     self.binder_index,

compiler/rustc_traits/src/chalk/lowering.rs

@@ -353,8 +353,8 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::Ty<RustInterner<'tcx>>> for Ty<'tcx> {
             ty::Tuple(types) => {
                 chalk_ir::TyKind::Tuple(types.len(), types.as_substs().lower_into(interner))
             }
-            ty::Projection(proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
+            ty::Alias(ty::Projection, proj) => chalk_ir::TyKind::Alias(proj.lower_into(interner)),
-            ty::Opaque(ty::AliasTy { def_id, substs }) => {
+            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
                 chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
                     opaque_ty_id: chalk_ir::OpaqueTyId(def_id),
                     substitution: substs.lower_into(interner),
@@ -442,14 +442,14 @@ impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
                 mutbl.lower_into(interner),
             ),
             TyKind::Str => ty::Str,
-            TyKind::OpaqueType(opaque_ty, substitution) => ty::Opaque(ty::AliasTy {
+            TyKind::OpaqueType(opaque_ty, substitution) => ty::Alias(
-                def_id: opaque_ty.0,
+                ty::Opaque,
-                substs: substitution.lower_into(interner),
+                ty::AliasTy { def_id: opaque_ty.0, substs: substitution.lower_into(interner) },
-            }),
+            ),
-            TyKind::AssociatedType(assoc_ty, substitution) => ty::Projection(ty::AliasTy {
+            TyKind::AssociatedType(assoc_ty, substitution) => ty::Alias(
-                substs: substitution.lower_into(interner),
+                ty::Projection,
-                def_id: assoc_ty.0,
+                ty::AliasTy { substs: substitution.lower_into(interner), def_id: assoc_ty.0 },
-            }),
+            ),
             TyKind::Foreign(def_id) => ty::Foreign(def_id.0),
             TyKind::Error => return interner.tcx.ty_error(),
             TyKind::Placeholder(placeholder) => ty::Placeholder(ty::Placeholder {
@@ -457,14 +457,20 @@ impl<'tcx> LowerInto<'tcx, Ty<'tcx>> for &chalk_ir::Ty<RustInterner<'tcx>> {
                 name: ty::BoundVar::from_usize(placeholder.idx),
             }),
             TyKind::Alias(alias_ty) => match alias_ty {
-                chalk_ir::AliasTy::Projection(projection) => ty::Projection(ty::AliasTy {
+                chalk_ir::AliasTy::Projection(projection) => ty::Alias(
-                    def_id: projection.associated_ty_id.0,
+                    ty::Projection,
-                    substs: projection.substitution.lower_into(interner),
+                    ty::AliasTy {
-                }),
+                        def_id: projection.associated_ty_id.0,
-                chalk_ir::AliasTy::Opaque(opaque) => ty::Opaque(ty::AliasTy {
+                        substs: projection.substitution.lower_into(interner),
-                    def_id: opaque.opaque_ty_id.0,
+                    },
-                    substs: opaque.substitution.lower_into(interner),
+                ),
-                }),
+                chalk_ir::AliasTy::Opaque(opaque) => ty::Alias(
+                    ty::Opaque,
+                    ty::AliasTy {
+                        def_id: opaque.opaque_ty_id.0,
+                        substs: opaque.substitution.lower_into(interner),
+                    },
+                ),
             },
             TyKind::Function(_quantified_ty) => unimplemented!(),
             TyKind::BoundVar(_bound) => ty::Bound(

compiler/rustc_traits/src/dropck_outlives.rs

@@ -112,7 +112,7 @@ fn dropck_outlives<'tcx>(
 
                     // A projection that we couldn't resolve - it
                     // might have a destructor.
-                    ty::Projection(..) | ty::Opaque(..) => {
+                    ty::Alias(ty::Projection, ..) | ty::Alias(ty::Opaque, ..) => {
                         result.kinds.push(ty.into());
                     }
 
@@ -268,7 +268,7 @@ fn dtorck_constraint_for_ty<'tcx>(
         }
 
         // Types that can't be resolved. Pass them forward.
-        ty::Projection(..) | ty::Opaque(..) | ty::Param(..) => {
+        ty::Alias(ty::Projection, ..) | ty::Alias(ty::Opaque, ..) | ty::Param(..) => {
             constraints.dtorck_types.push(ty);
         }
 

compiler/rustc_ty_utils/src/layout.rs

@@ -444,7 +444,7 @@ fn layout_of_uncached<'tcx>(
         }
 
         // Types with no meaningful known layout.
-        ty::Projection(_) | ty::Opaque(..) => {
+        ty::Alias(ty::Projection, _) | ty::Alias(ty::Opaque, ..) => {
             // NOTE(eddyb) `layout_of` query should've normalized these away,
             // if that was possible, so there's no reason to try again here.
             return Err(LayoutError::Unknown(ty));

compiler/rustc_ty_utils/src/needs_drop.rs

@@ -152,7 +152,10 @@ where
                             queue_type(self, required);
                         }
                     }
-                    ty::Array(..) | ty::Opaque(..) | ty::Projection(..) | ty::Param(_) => {
+                    ty::Array(..)
+                    | ty::Alias(ty::Opaque, ..)
+                    | ty::Alias(ty::Projection, ..)
+                    | ty::Param(_) => {
                         if ty == component {
                             // Return the type to the caller: they may be able
                             // to normalize further than we can.

compiler/rustc_ty_utils/src/ty.rs

@@ -37,7 +37,7 @@ fn sized_constraint_for_ty<'tcx>(
                 .collect()
         }
 
-        Projection(..) | Opaque(..) => {
+        Alias(..) => {
             // must calculate explicitly.
             // FIXME: consider special-casing always-Sized projections
             vec![ty]

compiler/rustc_type_ir/src/lib.rs

@@ -42,9 +42,8 @@ pub trait Interner {
     type ListBinderExistentialPredicate: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type BinderListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type ListTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
-    type ProjectionTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
+    type AliasTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type ParamTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
-    type OpaqueTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type BoundTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type PlaceholderType: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;
     type InferTy: Clone + Debug + Hash + PartialEq + Eq + PartialOrd + Ord;

compiler/rustc_type_ir/src/sty.rs

@@ -19,19 +19,8 @@ use rustc_data_structures::stable_hasher::HashStable;
 use rustc_serialize::{Decodable, Decoder, Encodable};
 
 /// Specifies how a trait object is represented.
-#[derive(
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
-    Clone,
+#[derive(Encodable, Decodable, HashStable_Generic)]
-    Copy,
-    PartialEq,
-    Eq,
-    PartialOrd,
-    Ord,
-    Hash,
-    Debug,
-    Encodable,
-    Decodable,
-    HashStable_Generic
-)]
 pub enum DynKind {
     /// An unsized `dyn Trait` object
     Dyn,
@@ -46,6 +35,13 @@ pub enum DynKind {
     DynStar,
 }
 
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Encodable, Decodable, HashStable_Generic)]
+pub enum AliasKind {
+    Projection,
+    Opaque,
+}
+
 /// Defines the kinds of types used by the type system.
 ///
 /// Types written by the user start out as `hir::TyKind` and get
@@ -171,19 +167,7 @@ pub enum TyKind<I: Interner> {
     Tuple(I::ListTy),
 
     /// A projection or opaque type. Both of these types
-    Projection(I::ProjectionTy),
+    Alias(AliasKind, I::AliasTy),
-
-    /// Opaque (`impl Trait`) type found in a return type.
-    ///
-    /// The `DefId` comes either from
-    /// * the `impl Trait` ast::Ty node,
-    /// * or the `type Foo = impl Trait` declaration
-    ///
-    /// For RPIT the substitutions are for the generics of the function,
-    /// while for TAIT it is used for the generic parameters of the alias.
-    ///
-    /// During codegen, `tcx.type_of(def_id)` can be used to get the underlying type.
-    Opaque(I::OpaqueTy),
 
     /// A type parameter; for example, `T` in `fn f<T>(x: T) {}`.
     Param(I::ParamTy),
@@ -251,13 +235,12 @@ const fn tykind_discriminant<I: Interner>(value: &TyKind<I>) -> usize {
         GeneratorWitness(_) => 17,
         Never => 18,
         Tuple(_) => 19,
-        Projection(_) => 20,
+        Alias(_, _) => 20,
-        Opaque(_) => 21,
+        Param(_) => 21,
-        Param(_) => 22,
+        Bound(_, _) => 22,
-        Bound(_, _) => 23,
+        Placeholder(_) => 23,
-        Placeholder(_) => 24,
+        Infer(_) => 24,
-        Infer(_) => 25,
+        Error(_) => 25,
-        Error(_) => 26,
     }
 }
 
@@ -285,8 +268,7 @@ impl<I: Interner> Clone for TyKind<I> {
             GeneratorWitness(g) => GeneratorWitness(g.clone()),
             Never => Never,
             Tuple(t) => Tuple(t.clone()),
-            Projection(p) => Projection(p.clone()),
+            Alias(k, p) => Alias(*k, p.clone()),
-            Opaque(o) => Opaque(o.clone()),
             Param(p) => Param(p.clone()),
             Bound(d, b) => Bound(d.clone(), b.clone()),
             Placeholder(p) => Placeholder(p.clone()),
@@ -322,8 +304,7 @@ impl<I: Interner> PartialEq for TyKind<I> {
                 }
                 (GeneratorWitness(a_g), GeneratorWitness(b_g)) => a_g == b_g,
                 (Tuple(a_t), Tuple(b_t)) => a_t == b_t,
-                (Projection(a_p), Projection(b_p)) => a_p == b_p,
+                (Alias(a_i, a_p), Alias(b_i, b_p)) => a_i == b_i && a_p == b_p,
-                (Opaque(a_o), Opaque(b_o)) => a_o == b_o,
                 (Param(a_p), Param(b_p)) => a_p == b_p,
                 (Bound(a_d, a_b), Bound(b_d, b_b)) => a_d == b_d && a_b == b_b,
                 (Placeholder(a_p), Placeholder(b_p)) => a_p == b_p,
@@ -380,8 +361,7 @@ impl<I: Interner> Ord for TyKind<I> {
                 }
                 (GeneratorWitness(a_g), GeneratorWitness(b_g)) => a_g.cmp(b_g),
                 (Tuple(a_t), Tuple(b_t)) => a_t.cmp(b_t),
-                (Projection(a_p), Projection(b_p)) => a_p.cmp(b_p),
+                (Alias(a_i, a_p), Alias(b_i, b_p)) => a_i.cmp(b_i).then_with(|| a_p.cmp(b_p)),
-                (Opaque(a_o), Opaque(b_o)) => a_o.cmp(b_o),
                 (Param(a_p), Param(b_p)) => a_p.cmp(b_p),
                 (Bound(a_d, a_b), Bound(b_d, b_b)) => a_d.cmp(b_d).then_with(|| a_b.cmp(b_b)),
                 (Placeholder(a_p), Placeholder(b_p)) => a_p.cmp(b_p),
@@ -442,9 +422,9 @@ impl<I: Interner> hash::Hash for TyKind<I> {
             }
             GeneratorWitness(g) => g.hash(state),
             Tuple(t) => t.hash(state),
-            Projection(p) => p.hash(state),
+            Alias(i, p) => {
-            Opaque(o) => {
+                i.hash(state);
-                o.hash(state);
+                p.hash(state);
             }
             Param(p) => p.hash(state),
             Bound(d, b) => {
@@ -483,8 +463,7 @@ impl<I: Interner> fmt::Debug for TyKind<I> {
             GeneratorWitness(g) => f.debug_tuple_field1_finish("GeneratorWitness", g),
             Never => f.write_str("Never"),
             Tuple(t) => f.debug_tuple_field1_finish("Tuple", t),
-            Projection(p) => f.debug_tuple_field1_finish("Projection", p),
+            Alias(i, a) => f.debug_tuple_field2_finish("Alias", i, a),
-            Opaque(o) => f.debug_tuple_field1_finish("Opaque", o),
             Param(p) => f.debug_tuple_field1_finish("Param", p),
             Bound(d, b) => f.debug_tuple_field2_finish("Bound", d, b),
             Placeholder(p) => f.debug_tuple_field1_finish("Placeholder", p),
@@ -511,9 +490,8 @@ where
     I::ListBinderExistentialPredicate: Encodable<E>,
     I::BinderListTy: Encodable<E>,
     I::ListTy: Encodable<E>,
-    I::ProjectionTy: Encodable<E>,
+    I::AliasTy: Encodable<E>,
     I::ParamTy: Encodable<E>,
-    I::OpaqueTy: Encodable<E>,
     I::BoundTy: Encodable<E>,
     I::PlaceholderType: Encodable<E>,
     I::InferTy: Encodable<E>,
@@ -585,12 +563,10 @@ where
             Tuple(substs) => e.emit_enum_variant(disc, |e| {
                 substs.encode(e);
             }),
-            Projection(p) => e.emit_enum_variant(disc, |e| {
+            Alias(k, p) => e.emit_enum_variant(disc, |e| {
+                k.encode(e);
                 p.encode(e);
             }),
-            Opaque(o) => e.emit_enum_variant(disc, |e| {
-                o.encode(e);
-            }),
             Param(p) => e.emit_enum_variant(disc, |e| {
                 p.encode(e);
             }),
@@ -628,9 +604,9 @@ where
     I::ListBinderExistentialPredicate: Decodable<D>,
     I::BinderListTy: Decodable<D>,
     I::ListTy: Decodable<D>,
-    I::ProjectionTy: Decodable<D>,
+    I::AliasTy: Decodable<D>,
     I::ParamTy: Decodable<D>,
-    I::OpaqueTy: Decodable<D>,
+    I::AliasTy: Decodable<D>,
     I::BoundTy: Decodable<D>,
     I::PlaceholderType: Decodable<D>,
     I::InferTy: Decodable<D>,
@@ -659,8 +635,7 @@ where
             17 => GeneratorWitness(Decodable::decode(d)),
             18 => Never,
             19 => Tuple(Decodable::decode(d)),
-            20 => Projection(Decodable::decode(d)),
+            20 => Alias(Decodable::decode(d), Decodable::decode(d)),
-            21 => Opaque(Decodable::decode(d)),
             22 => Param(Decodable::decode(d)),
             23 => Bound(Decodable::decode(d), Decodable::decode(d)),
             24 => Placeholder(Decodable::decode(d)),
@@ -694,10 +669,9 @@ where
     I::Mutability: HashStable<CTX>,
     I::BinderListTy: HashStable<CTX>,
     I::ListTy: HashStable<CTX>,
-    I::ProjectionTy: HashStable<CTX>,
+    I::AliasTy: HashStable<CTX>,
     I::BoundTy: HashStable<CTX>,
     I::ParamTy: HashStable<CTX>,
-    I::OpaqueTy: HashStable<CTX>,
     I::PlaceholderType: HashStable<CTX>,
     I::InferTy: HashStable<CTX>,
     I::ErrorGuaranteed: HashStable<CTX>,
@@ -772,12 +746,10 @@ where
             Tuple(substs) => {
                 substs.hash_stable(__hcx, __hasher);
             }
-            Projection(p) => {
+            Alias(k, p) => {
+                k.hash_stable(__hcx, __hasher);
                 p.hash_stable(__hcx, __hasher);
             }
-            Opaque(o) => {
-                o.hash_stable(__hcx, __hasher);
-            }
             Param(p) => {
                 p.hash_stable(__hcx, __hasher);
             }

src/librustdoc/clean/mod.rs

@@ -1487,7 +1487,9 @@ fn clean_qpath<'tcx>(hir_ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> Type
         hir::QPath::TypeRelative(qself, segment) => {
             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
             let res = match ty.kind() {
-                ty::Projection(proj) => Res::Def(DefKind::Trait, proj.trait_ref(cx.tcx).def_id),
+                ty::Alias(ty::Projection, proj) => {
+                    Res::Def(DefKind::Trait, proj.trait_ref(cx.tcx).def_id)
+                }
                 // Rustdoc handles `ty::Error`s by turning them into `Type::Infer`s.
                 ty::Error(_) => return Type::Infer,
                 // Otherwise, this is an inherent associated type.
@@ -1823,7 +1825,7 @@ pub(crate) fn clean_middle_ty<'tcx>(
             Tuple(t.iter().map(|t| clean_middle_ty(bound_ty.rebind(t), cx, None)).collect())
         }
 
-        ty::Projection(ref data) => clean_projection(bound_ty.rebind(*data), cx, def_id),
+        ty::Alias(ty::Projection, ref data) => clean_projection(bound_ty.rebind(*data), cx, def_id),
 
         ty::Param(ref p) => {
             if let Some(bounds) = cx.impl_trait_bounds.remove(&p.index.into()) {
@@ -1833,7 +1835,7 @@ pub(crate) fn clean_middle_ty<'tcx>(
             }
         }
 
-        ty::Opaque(ty::AliasTy { def_id, substs }) => {
+        ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs }) => {
             // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
             // by looking up the bounds associated with the def_id.
             let bounds = cx

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -538,11 +538,10 @@ impl<'a, 'tcx> LinkCollector<'a, 'tcx> {
             ty::Adt(ty::AdtDef(Interned(&ty::AdtDefData { did, .. }, _)), _) | ty::Foreign(did) => {
                 Res::from_def_id(self.cx.tcx, did)
             }
-            ty::Projection(_)
+            ty::Alias(..)
             | ty::Closure(..)
             | ty::Generator(..)
             | ty::GeneratorWitness(_)
-            | ty::Opaque(..)
             | ty::Dynamic(..)
             | ty::Param(_)
             | ty::Bound(..)

src/test/ui-fulldeps/internal-lints/ty_tykind_usage.rs

@@ -33,8 +33,7 @@ fn main() {
         TyKind::GeneratorWitness(..) => (), //~ ERROR usage of `ty::TyKind::<kind>`
         TyKind::Never => (),                //~ ERROR usage of `ty::TyKind::<kind>`
         TyKind::Tuple(..) => (),            //~ ERROR usage of `ty::TyKind::<kind>`
-        TyKind::Projection(..) => (),       //~ ERROR usage of `ty::TyKind::<kind>`
+        TyKind::Alias(..) => (),            //~ ERROR usage of `ty::TyKind::<kind>`
-        TyKind::Opaque(..) => (),           //~ ERROR usage of `ty::TyKind::<kind>`
         TyKind::Param(..) => (),            //~ ERROR usage of `ty::TyKind::<kind>`
         TyKind::Bound(..) => (),            //~ ERROR usage of `ty::TyKind::<kind>`
         TyKind::Placeholder(..) => (),      //~ ERROR usage of `ty::TyKind::<kind>`

src/test/ui-fulldeps/internal-lints/ty_tykind_usage.stderr

@@ -133,53 +133,47 @@ LL |         TyKind::Tuple(..) => (),
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:36:9
    |
-LL |         TyKind::Projection(..) => (),
+LL |         TyKind::Alias(..) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:37:9
    |
-LL |         TyKind::Opaque(..) => (),
+LL |         TyKind::Param(..) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:38:9
    |
-LL |         TyKind::Param(..) => (),
+LL |         TyKind::Bound(..) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:39:9
    |
-LL |         TyKind::Bound(..) => (),
+LL |         TyKind::Placeholder(..) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:40:9
    |
-LL |         TyKind::Placeholder(..) => (),
+LL |         TyKind::Infer(..) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
   --> $DIR/ty_tykind_usage.rs:41:9
    |
-LL |         TyKind::Infer(..) => (),
-   |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
-
-error: usage of `ty::TyKind::<kind>`
-  --> $DIR/ty_tykind_usage.rs:42:9
-   |
 LL |         TyKind::Error(_) => (),
    |         ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind::<kind>`
-  --> $DIR/ty_tykind_usage.rs:47:12
+  --> $DIR/ty_tykind_usage.rs:46:12
    |
 LL |     if let TyKind::Int(int_ty) = kind {}
    |            ^^^^^^ help: try using `ty::<kind>` directly: `ty`
 
 error: usage of `ty::TyKind`
-  --> $DIR/ty_tykind_usage.rs:49:24
+  --> $DIR/ty_tykind_usage.rs:48:24
    |
 LL |     fn ty_kind(ty_bad: TyKind<'_>, ty_good: Ty<'_>) {}
    |                        ^^^^^^^^^^
@@ -187,7 +181,7 @@ LL |     fn ty_kind(ty_bad: TyKind<'_>, ty_good: Ty<'_>) {}
    = help: try using `Ty` instead
 
 error: usage of `ty::TyKind`
-  --> $DIR/ty_tykind_usage.rs:51:37
+  --> $DIR/ty_tykind_usage.rs:50:37
    |
 LL |     fn ir_ty_kind<I: Interner>(bad: IrTyKind<I>) -> IrTyKind<I> {
    |                                     ^^^^^^^^^^^
@@ -195,7 +189,7 @@ LL |     fn ir_ty_kind<I: Interner>(bad: IrTyKind<I>) -> IrTyKind<I> {
    = help: try using `Ty` instead
 
 error: usage of `ty::TyKind`
-  --> $DIR/ty_tykind_usage.rs:51:53
+  --> $DIR/ty_tykind_usage.rs:50:53
    |
 LL |     fn ir_ty_kind<I: Interner>(bad: IrTyKind<I>) -> IrTyKind<I> {
    |                                                     ^^^^^^^^^^^
@@ -203,12 +197,12 @@ LL |     fn ir_ty_kind<I: Interner>(bad: IrTyKind<I>) -> IrTyKind<I> {
    = help: try using `Ty` instead
 
 error: usage of `ty::TyKind::<kind>`
-  --> $DIR/ty_tykind_usage.rs:54:9
+  --> $DIR/ty_tykind_usage.rs:53:9
    |
 LL |         IrTyKind::Bool
    |         --------^^^^^^
    |         |
    |         help: try using `ty::<kind>` directly: `ty`
 
-error: aborting due to 33 previous errors
+error: aborting due to 32 previous errors
 

src/tools/clippy/clippy_lints/src/dereference.rs

@@ -1244,7 +1244,7 @@ fn is_mixed_projection_predicate<'tcx>(
         let mut projection_ty = projection_predicate.projection_ty;
         loop {
             match projection_ty.self_ty().kind() {
-                ty::Projection(inner_projection_ty) => {
+                ty::Alias(ty::Projection, inner_projection_ty) => {
                     projection_ty = *inner_projection_ty;
                 }
                 ty::Param(param_ty) => {
@@ -1390,8 +1390,8 @@ fn ty_auto_deref_stability<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, precedenc
                 continue;
             },
             ty::Param(_) => TyPosition::new_deref_stable_for_result(precedence, ty),
-            ty::Projection(_) if ty.has_non_region_param() => TyPosition::new_deref_stable_for_result(precedence, ty),
+            ty::Alias(ty::Projection, _) if ty.has_non_region_param() => TyPosition::new_deref_stable_for_result(precedence, ty),
-            ty::Infer(_) | ty::Error(_) | ty::Bound(..) | ty::Opaque(..) | ty::Placeholder(_) | ty::Dynamic(..) => {
+            ty::Infer(_) | ty::Error(_) | ty::Bound(..) | ty::Alias(ty::Opaque, ..) | ty::Placeholder(_) | ty::Dynamic(..) => {
                 Position::ReborrowStable(precedence).into()
             },
             ty::Adt(..) if ty.has_placeholders() || ty.has_opaque_types() => {
@@ -1417,7 +1417,7 @@ fn ty_auto_deref_stability<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, precedenc
             | ty::Closure(..)
             | ty::Never
             | ty::Tuple(_)
-            | ty::Projection(_) => {
+            | ty::Alias(ty::Projection, _) => {
                 Position::DerefStable(precedence, ty.is_sized(cx.tcx, cx.param_env.without_caller_bounds())).into()
             },
         };