Make const bound handling more like types/regions.

Currently there is `Ty` and `BoundTy`, and `Region` and `BoundRegion`,
and `Const` and... `BoundVar`. An annoying inconsistency.

This commit repurposes the existing `BoundConst`, which was barely used,
so it's the partner to `Const`. Unlike `BoundTy`/`BoundRegion` it lacks
a `kind` field but it's still nice to have because it makes the const
code more similar to the ty/region code everywhere.

The commit also removes `impl From<BoundVar> for BoundTy`, which has a
single use and doesn't seem worth it.

These changes fix the "FIXME: We really should have a separate
`BoundConst` for consts".

21 files changed, 82 insertions, 69 deletions

diff --git a/compiler/rustc_borrowck/src/type_check/relate_tys.rs b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
index e023300f1c2..bb72d1d52f3 100644
--- a/compiler/rustc_borrowck/src/type_check/relate_tys.rs
+++ b/compiler/rustc_borrowck/src/type_check/relate_tys.rs
@@ -187,7 +187,7 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
                 types: &mut |_bound_ty: ty::BoundTy| {
                     unreachable!("we only replace regions in nll_relate, not types")
                 },
-                consts: &mut |_bound_var: ty::BoundVar| {
+                consts: &mut |_bound_const: ty::BoundConst| {
                     unreachable!("we only replace regions in nll_relate, not consts")
                 },
             };
@@ -226,7 +226,7 @@ impl<'a, 'b, 'tcx> NllTypeRelating<'a, 'b, 'tcx> {
             types: &mut |_bound_ty: ty::BoundTy| {
                 unreachable!("we only replace regions in nll_relate, not types")
             },
-            consts: &mut |_bound_var: ty::BoundVar| {
+            consts: &mut |_bound_const: ty::BoundConst| {
                 unreachable!("we only replace regions in nll_relate, not consts")
             },
         };
diff --git a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
index e24426f9fed..13d690054ce 100644
--- a/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
+++ b/compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
@@ -2498,7 +2498,7 @@ fn param_env_with_gat_bounds<'tcx>(
                     ty::Const::new_bound(
                         tcx,
                         ty::INNERMOST,
-                        ty::BoundVar::from_usize(bound_vars.len() - 1),
+                        ty::BoundConst { var: ty::BoundVar::from_usize(bound_vars.len() - 1) },
                     )
                     .into()
                 }
diff --git a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
index 548ba343aae..ba54fa8cc0d 100644
--- a/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
+++ b/compiler/rustc_hir_analysis/src/collect/item_bounds.rs
@@ -189,7 +189,7 @@ fn remap_gat_vars_and_recurse_into_nested_projections<'tcx>(
             }
             ty::GenericArgKind::Const(ct) => {
                 if let ty::ConstKind::Bound(ty::INNERMOST, bv) = ct.kind() {
-                    mapping.insert(bv, tcx.mk_param_from_def(param))
+                    mapping.insert(bv.var, tcx.mk_param_from_def(param))
                 } else {
                     return None;
                 }
@@ -307,16 +307,16 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for MapAndCompressBoundVars<'tcx> {
             return ct;
         }
 
-        if let ty::ConstKind::Bound(binder, old_var) = ct.kind()
+        if let ty::ConstKind::Bound(binder, old_bound) = ct.kind()
             && self.binder == binder
         {
-            let mapped = if let Some(mapped) = self.mapping.get(&old_var) {
+            let mapped = if let Some(mapped) = self.mapping.get(&old_bound.var) {
                 mapped.expect_const()
             } else {
                 let var = ty::BoundVar::from_usize(self.still_bound_vars.len());
                 self.still_bound_vars.push(ty::BoundVariableKind::Const);
-                let mapped = ty::Const::new_bound(self.tcx, ty::INNERMOST, var);
-                self.mapping.insert(old_var, mapped.into());
+                let mapped = ty::Const::new_bound(self.tcx, ty::INNERMOST, ty::BoundConst { var });
+                self.mapping.insert(old_bound.var, mapped.into());
                 mapped
             };
 
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
index 7760642d8fb..386e1091ac4 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/bounds.rs
@@ -1077,7 +1077,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for GenericParamAndBoundVarCollector<'_, 't
             ty::ConstKind::Param(param) => {
                 self.params.insert(param.index);
             }
-            ty::ConstKind::Bound(db, ty::BoundVar { .. }) if db >= self.depth => {
+            ty::ConstKind::Bound(db, _) if db >= self.depth => {
                 let guar = self.cx.dcx().delayed_bug("unexpected escaping late-bound const var");
                 return ControlFlow::Break(guar);
             }
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
index d7687998358..d93f3c5f508 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs
@@ -2107,9 +2107,11 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 let name = tcx.item_name(param_def_id);
                 ty::Const::new_param(tcx, ty::ParamConst::new(index, name))
             }
-            Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => {
-                ty::Const::new_bound(tcx, debruijn, ty::BoundVar::from_u32(index))
-            }
+            Some(rbv::ResolvedArg::LateBound(debruijn, index, _)) => ty::Const::new_bound(
+                tcx,
+                debruijn,
+                ty::BoundConst { var: ty::BoundVar::from_u32(index) },
+            ),
             Some(rbv::ResolvedArg::Error(guar)) => ty::Const::new_error(tcx, guar),
             arg => bug!("unexpected bound var resolution for {:?}: {arg:?}", path_hir_id),
         }
diff --git a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
index 060447ba720..a4c6d078125 100644
--- a/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
+++ b/compiler/rustc_infer/src/infer/canonical/canonicalizer.rs
@@ -752,7 +752,8 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
     ) -> Ty<'tcx> {
         debug_assert!(!self.infcx.is_some_and(|infcx| ty_var != infcx.shallow_resolve(ty_var)));
         let var = self.canonical_var(var_kind, ty_var.into());
-        Ty::new_bound(self.tcx, self.binder_index, var.into())
+        let bt = ty::BoundTy { var, kind: ty::BoundTyKind::Anon };
+        Ty::new_bound(self.tcx, self.binder_index, bt)
     }
 
     /// Given a type variable `const_var` of the given kind, first check
@@ -768,6 +769,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
             !self.infcx.is_some_and(|infcx| ct_var != infcx.shallow_resolve_const(ct_var))
         );
         let var = self.canonical_var(var_kind, ct_var.into());
-        ty::Const::new_bound(self.tcx, self.binder_index, var)
+        let bc = ty::BoundConst { var };
+        ty::Const::new_bound(self.tcx, self.binder_index, bc)
     }
 }
diff --git a/compiler/rustc_infer/src/infer/canonical/instantiate.rs b/compiler/rustc_infer/src/infer/canonical/instantiate.rs
index 2385c68ef6b..cc052fbd85c 100644
--- a/compiler/rustc_infer/src/infer/canonical/instantiate.rs
+++ b/compiler/rustc_infer/src/infer/canonical/instantiate.rs
@@ -133,7 +133,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for CanonicalInstantiator<'tcx> {
     fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
         match ct.kind() {
             ty::ConstKind::Bound(debruijn, bound_const) if debruijn == self.current_index => {
-                self.var_values[bound_const.as_usize()].expect_const()
+                self.var_values[bound_const.var.as_usize()].expect_const()
             }
             _ => ct.super_fold_with(self),
         }
@@ -217,7 +217,7 @@ fn highest_var_in_clauses<'tcx>(c: ty::Clauses<'tcx>) -> usize {
             if let ty::ConstKind::Bound(debruijn, bound_const) = ct.kind()
                 && debruijn == self.current_index
             {
-                self.max_var = self.max_var.max(bound_const.as_usize());
+                self.max_var = self.max_var.max(bound_const.var.as_usize());
             } else if ct.has_vars_bound_at_or_above(self.current_index) {
                 ct.super_visit_with(self);
             }
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index 6be53c948c8..73b1ca6c691 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -433,12 +433,12 @@ impl<'tcx> InferCtxt<'tcx> {
                 }
                 GenericArgKind::Lifetime(result_value) => {
                     // e.g., here `result_value` might be `'?1` in the example above...
-                    if let ty::ReBound(debruijn, br) = result_value.kind() {
+                    if let ty::ReBound(debruijn, b) = result_value.kind() {
                         // ... in which case we would set `canonical_vars[0]` to `Some('static)`.
 
                         // We only allow a `ty::INNERMOST` index in generic parameters.
                         assert_eq!(debruijn, ty::INNERMOST);
-                        opt_values[br.var] = Some(*original_value);
+                        opt_values[b.var] = Some(*original_value);
                     }
                 }
                 GenericArgKind::Const(result_value) => {
@@ -447,7 +447,7 @@ impl<'tcx> InferCtxt<'tcx> {
 
                         // We only allow a `ty::INNERMOST` index in generic parameters.
                         assert_eq!(debruijn, ty::INNERMOST);
-                        opt_values[b] = Some(*original_value);
+                        opt_values[b.var] = Some(*original_value);
                     }
                 }
             }
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index 2d269e320b6..41297e8ffca 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -1208,8 +1208,8 @@ impl<'tcx> InferCtxt<'tcx> {
             fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
                 self.args[bt.var.index()].expect_ty()
             }
-            fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
-                self.args[bv.index()].expect_const()
+            fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
+                self.args[bc.var.index()].expect_const()
             }
         }
         let delegate = ToFreshVars { args };
diff --git a/compiler/rustc_infer/src/infer/relate/higher_ranked.rs b/compiler/rustc_infer/src/infer/relate/higher_ranked.rs
index 2143f72a3b0..16fe591b29b 100644
--- a/compiler/rustc_infer/src/infer/relate/higher_ranked.rs
+++ b/compiler/rustc_infer/src/infer/relate/higher_ranked.rs
@@ -45,10 +45,10 @@ impl<'tcx> InferCtxt<'tcx> {
                     ty::PlaceholderType { universe: next_universe, bound: bound_ty },
                 )
             },
-            consts: &mut |bound_var: ty::BoundVar| {
+            consts: &mut |bound_const: ty::BoundConst| {
                 ty::Const::new_placeholder(
                     self.tcx,
-                    ty::PlaceholderConst { universe: next_universe, bound: bound_var },
+                    ty::PlaceholderConst { universe: next_universe, bound: bound_const },
                 )
             },
         };
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index fd1aa4042bc..614b6471f18 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -93,9 +93,9 @@ impl<'tcx> Const<'tcx> {
     pub fn new_bound(
         tcx: TyCtxt<'tcx>,
         debruijn: ty::DebruijnIndex,
-        var: ty::BoundVar,
+        bound_const: ty::BoundConst,
     ) -> Const<'tcx> {
-        Const::new(tcx, ty::ConstKind::Bound(debruijn, var))
+        Const::new(tcx, ty::ConstKind::Bound(debruijn, bound_const))
     }
 
     #[inline]
@@ -168,12 +168,16 @@ impl<'tcx> rustc_type_ir::inherent::Const<TyCtxt<'tcx>> for Const<'tcx> {
         Const::new_var(tcx, vid)
     }
 
-    fn new_bound(interner: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self {
-        Const::new_bound(interner, debruijn, var)
+    fn new_bound(
+        interner: TyCtxt<'tcx>,
+        debruijn: ty::DebruijnIndex,
+        bound_const: ty::BoundConst,
+    ) -> Self {
+        Const::new_bound(interner, debruijn, bound_const)
     }
 
     fn new_anon_bound(tcx: TyCtxt<'tcx>, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self {
-        Const::new_bound(tcx, debruijn, var)
+        Const::new_bound(tcx, debruijn, ty::BoundConst { var })
     }
 
     fn new_placeholder(tcx: TyCtxt<'tcx>, placeholder: ty::PlaceholderConst) -> Self {
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 6f21160d1f6..466b3f191c0 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -152,7 +152,7 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
     type PlaceholderConst = ty::PlaceholderConst;
 
     type ParamConst = ty::ParamConst;
-    type BoundConst = ty::BoundVar;
+    type BoundConst = ty::BoundConst;
     type ValueConst = ty::Value<'tcx>;
     type ExprConst = ty::Expr<'tcx>;
     type ValTree = ty::ValTree<'tcx>;
diff --git a/compiler/rustc_middle/src/ty/fold.rs b/compiler/rustc_middle/src/ty/fold.rs
index b2057fa36d7..7d56ec1635f 100644
--- a/compiler/rustc_middle/src/ty/fold.rs
+++ b/compiler/rustc_middle/src/ty/fold.rs
@@ -3,7 +3,7 @@ use rustc_hir::def_id::DefId;
 use rustc_type_ir::data_structures::DelayedMap;
 
 use crate::ty::{
-    self, Binder, BoundTy, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
+    self, Binder, BoundConst, BoundTy, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
     TypeVisitableExt,
 };
 
@@ -60,7 +60,7 @@ where
 pub trait BoundVarReplacerDelegate<'tcx> {
     fn replace_region(&mut self, br: ty::BoundRegion) -> ty::Region<'tcx>;
     fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx>;
-    fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx>;
+    fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx>;
 }
 
 /// A simple delegate taking 3 mutable functions. The used functions must
@@ -69,7 +69,7 @@ pub trait BoundVarReplacerDelegate<'tcx> {
 pub struct FnMutDelegate<'a, 'tcx> {
     pub regions: &'a mut (dyn FnMut(ty::BoundRegion) -> ty::Region<'tcx> + 'a),
     pub types: &'a mut (dyn FnMut(ty::BoundTy) -> Ty<'tcx> + 'a),
-    pub consts: &'a mut (dyn FnMut(ty::BoundVar) -> ty::Const<'tcx> + 'a),
+    pub consts: &'a mut (dyn FnMut(ty::BoundConst) -> ty::Const<'tcx> + 'a),
 }
 
 impl<'a, 'tcx> BoundVarReplacerDelegate<'tcx> for FnMutDelegate<'a, 'tcx> {
@@ -79,8 +79,8 @@ impl<'a, 'tcx> BoundVarReplacerDelegate<'tcx> for FnMutDelegate<'a, 'tcx> {
     fn replace_ty(&mut self, bt: ty::BoundTy) -> Ty<'tcx> {
         (self.types)(bt)
     }
-    fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
-        (self.consts)(bv)
+    fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
+        (self.consts)(bc)
     }
 }
 
@@ -300,7 +300,13 @@ impl<'tcx> TyCtxt<'tcx> {
                         ty::BoundTy { var: shift_bv(t.var), kind: t.kind },
                     )
                 },
-                consts: &mut |c| ty::Const::new_bound(self, ty::INNERMOST, shift_bv(c)),
+                consts: &mut |c| {
+                    ty::Const::new_bound(
+                        self,
+                        ty::INNERMOST,
+                        ty::BoundConst { var: shift_bv(c.var) },
+                    )
+                },
             },
         )
     }
@@ -343,12 +349,12 @@ impl<'tcx> TyCtxt<'tcx> {
                     .expect_ty();
                 Ty::new_bound(self.tcx, ty::INNERMOST, BoundTy { var, kind })
             }
-            fn replace_const(&mut self, bv: ty::BoundVar) -> ty::Const<'tcx> {
-                let entry = self.map.entry(bv);
+            fn replace_const(&mut self, bc: ty::BoundConst) -> ty::Const<'tcx> {
+                let entry = self.map.entry(bc.var);
                 let index = entry.index();
                 let var = ty::BoundVar::from_usize(index);
                 let () = entry.or_insert_with(|| ty::BoundVariableKind::Const).expect_const();
-                ty::Const::new_bound(self.tcx, ty::INNERMOST, var)
+                ty::Const::new_bound(self.tcx, ty::INNERMOST, BoundConst { var })
             }
         }
 
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index bb70c61cd14..fab020547ad 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -968,34 +968,43 @@ impl<'tcx> rustc_type_ir::inherent::PlaceholderLike<TyCtxt<'tcx>> for Placeholde
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, HashStable)]
 #[derive(TyEncodable, TyDecodable)]
-pub struct BoundConst<'tcx> {
+pub struct BoundConst {
     pub var: BoundVar,
-    pub ty: Ty<'tcx>,
 }
 
-pub type PlaceholderConst = Placeholder<BoundVar>;
+impl<'tcx> rustc_type_ir::inherent::BoundVarLike<TyCtxt<'tcx>> for BoundConst {
+    fn var(self) -> BoundVar {
+        self.var
+    }
+
+    fn assert_eq(self, _var: ty::BoundVariableKind) {
+        unreachable!()
+    }
+}
+
+pub type PlaceholderConst = Placeholder<BoundConst>;
 
 impl<'tcx> rustc_type_ir::inherent::PlaceholderLike<TyCtxt<'tcx>> for PlaceholderConst {
-    type Bound = BoundVar;
+    type Bound = BoundConst;
 
     fn universe(self) -> UniverseIndex {
         self.universe
     }
 
     fn var(self) -> BoundVar {
-        self.bound
+        self.bound.var
     }
 
     fn with_updated_universe(self, ui: UniverseIndex) -> Self {
         Placeholder { universe: ui, ..self }
     }
 
-    fn new(ui: UniverseIndex, bound: BoundVar) -> Self {
+    fn new(ui: UniverseIndex, bound: BoundConst) -> Self {
         Placeholder { universe: ui, bound }
     }
 
     fn new_anon(ui: UniverseIndex, var: BoundVar) -> Self {
-        Placeholder { universe: ui, bound: var }
+        Placeholder { universe: ui, bound: BoundConst { var } }
     }
 }
 
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 4569596cfbe..ea84ea3af42 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -403,12 +403,6 @@ pub enum BoundTyKind {
     Param(DefId),
 }
 
-impl From<BoundVar> for BoundTy {
-    fn from(var: BoundVar) -> Self {
-        BoundTy { var, kind: BoundTyKind::Anon }
-    }
-}
-
 /// Constructors for `Ty`
 impl<'tcx> Ty<'tcx> {
     /// Avoid using this in favour of more specific `new_*` methods, where possible.
diff --git a/compiler/rustc_middle/src/ty/typeck_results.rs b/compiler/rustc_middle/src/ty/typeck_results.rs
index 88583407d25..6b187c5325a 100644
--- a/compiler/rustc_middle/src/ty/typeck_results.rs
+++ b/compiler/rustc_middle/src/ty/typeck_results.rs
@@ -789,10 +789,10 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
                         },
 
                         GenericArgKind::Lifetime(r) => match r.kind() {
-                            ty::ReBound(debruijn, br) => {
+                            ty::ReBound(debruijn, b) => {
                                 // We only allow a `ty::INNERMOST` index in generic parameters.
                                 assert_eq!(debruijn, ty::INNERMOST);
-                                cvar == br.var
+                                cvar == b.var
                             }
                             _ => false,
                         },
@@ -801,7 +801,7 @@ impl<'tcx> IsIdentity for CanonicalUserType<'tcx> {
                             ty::ConstKind::Bound(debruijn, b) => {
                                 // We only allow a `ty::INNERMOST` index in generic parameters.
                                 assert_eq!(debruijn, ty::INNERMOST);
-                                cvar == b
+                                cvar == b.var
                             }
                             _ => false,
                         },
diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs
index 07e78da37b3..d8aedf5c2bf 100644
--- a/compiler/rustc_trait_selection/src/traits/coherence.rs
+++ b/compiler/rustc_trait_selection/src/traits/coherence.rs
@@ -535,7 +535,10 @@ fn plug_infer_with_placeholders<'tcx>(
                         ct,
                         ty::Const::new_placeholder(
                             self.infcx.tcx,
-                            ty::Placeholder { universe: self.universe, bound: self.next_var() },
+                            ty::Placeholder {
+                                universe: self.universe,
+                                bound: ty::BoundConst { var: self.next_var() },
+                            },
                         ),
                     )
                 else {
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 9b5e59ce0fd..08315dbd21f 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -706,7 +706,10 @@ fn replace_param_and_infer_args_with_placeholder<'tcx>(
                 self.idx += 1;
                 ty::Const::new_placeholder(
                     self.tcx,
-                    ty::PlaceholderConst { universe: ty::UniverseIndex::ROOT, bound: idx },
+                    ty::PlaceholderConst {
+                        universe: ty::UniverseIndex::ROOT,
+                        bound: ty::BoundConst { var: idx },
+                    },
                 )
             } else {
                 c.super_fold_with(self)
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index c3d60ec45c4..83c0969762f 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -222,7 +222,7 @@ pub struct PlaceholderReplacer<'a, 'tcx> {
     infcx: &'a InferCtxt<'tcx>,
     mapped_regions: FxIndexMap<ty::PlaceholderRegion, ty::BoundRegion>,
     mapped_types: FxIndexMap<ty::PlaceholderType, ty::BoundTy>,
-    mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundVar>,
+    mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundConst>,
     universe_indices: &'a [Option<ty::UniverseIndex>],
     current_index: ty::DebruijnIndex,
 }
@@ -232,7 +232,7 @@ impl<'a, 'tcx> PlaceholderReplacer<'a, 'tcx> {
         infcx: &'a InferCtxt<'tcx>,
         mapped_regions: FxIndexMap<ty::PlaceholderRegion, ty::BoundRegion>,
         mapped_types: FxIndexMap<ty::PlaceholderType, ty::BoundTy>,
-        mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundVar>,
+        mapped_consts: FxIndexMap<ty::PlaceholderConst, ty::BoundConst>,
         universe_indices: &'a [Option<ty::UniverseIndex>],
         value: T,
     ) -> T {
diff --git a/compiler/rustc_type_ir/src/inherent.rs b/compiler/rustc_type_ir/src/inherent.rs
index 0e307e15d5b..1a6c99ce7de 100644
--- a/compiler/rustc_type_ir/src/inherent.rs
+++ b/compiler/rustc_type_ir/src/inherent.rs
@@ -251,7 +251,7 @@ pub trait Const<I: Interner<Const = Self>>:
 
     fn new_var(interner: I, var: ty::ConstVid) -> Self;
 
-    fn new_bound(interner: I, debruijn: ty::DebruijnIndex, var: I::BoundConst) -> Self;
+    fn new_bound(interner: I, debruijn: ty::DebruijnIndex, bound_const: I::BoundConst) -> Self;
 
     fn new_anon_bound(interner: I, debruijn: ty::DebruijnIndex, var: ty::BoundVar) -> Self;
 
diff --git a/compiler/rustc_type_ir/src/lib.rs b/compiler/rustc_type_ir/src/lib.rs
index a483c18813b..5c9cac5b21b 100644
--- a/compiler/rustc_type_ir/src/lib.rs
+++ b/compiler/rustc_type_ir/src/lib.rs
@@ -387,16 +387,6 @@ rustc_index::newtype_index! {
     pub struct BoundVar {}
 }
 
-impl<I: Interner> inherent::BoundVarLike<I> for BoundVar {
-    fn var(self) -> BoundVar {
-        self
-    }
-
-    fn assert_eq(self, _var: I::BoundVarKind) {
-        unreachable!("FIXME: We really should have a separate `BoundConst` for consts")
-    }
-}
-
 /// Represents the various closure traits in the language. This
 /// will determine the type of the environment (`self`, in the
 /// desugaring) argument that the closure expects.