1 files changed, 21 insertions, 28 deletions

diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index e60d7c730..214655807 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -36,7 +36,7 @@ use crate::{
     AliasEq, AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, DynTy, FnPointer, FnSig,
     ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause, QuantifiedWhereClauses,
     ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution, TraitEnvironment, TraitRef, Ty,
-    TyKind, TypeWalk, WhereClause,
+    TyBuilder, TyKind, TypeWalk, WhereClause,
 };
 
 #[derive(Debug)]
@@ -234,7 +234,7 @@ impl<'a> TyLoweringContext<'a> {
                         let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
                         let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
                         let generics = generics(self.db.upcast(), func.into());
-                        let parameters = Substitution::bound_vars(&generics, self.in_binders);
+                        let parameters = generics.bound_vars_subst(self.in_binders);
                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
                             opaque_ty_id,
                             substitution: parameters,
@@ -411,24 +411,16 @@ impl<'a> TyLoweringContext<'a> {
             TypeNs::SelfType(impl_id) => {
                 let generics = generics(self.db.upcast(), impl_id.into());
                 let substs = match self.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        Substitution::type_params_for_generics(self.db, &generics)
-                    }
-                    TypeParamLoweringMode::Variable => {
-                        Substitution::bound_vars(&generics, self.in_binders)
-                    }
+                    TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
+                    TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
                 };
                 self.db.impl_self_ty(impl_id).subst(&substs)
             }
             TypeNs::AdtSelfType(adt) => {
                 let generics = generics(self.db.upcast(), adt.into());
                 let substs = match self.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        Substitution::type_params_for_generics(self.db, &generics)
-                    }
-                    TypeParamLoweringMode::Variable => {
-                        Substitution::bound_vars(&generics, self.in_binders)
-                    }
+                    TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
+                    TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
                 };
                 self.db.ty(adt.into()).subst(&substs)
             }
@@ -478,12 +470,13 @@ impl<'a> TyLoweringContext<'a> {
                             TypeParamLoweringMode::Placeholder => {
                                 // if we're lowering to placeholders, we have to put
                                 // them in now
-                                let s = Substitution::type_params(
-                                    self.db,
+                                let generics = generics(
+                                    self.db.upcast(),
                                     self.resolver.generic_def().expect(
                                         "there should be generics if there's a generic param",
                                     ),
                                 );
+                                let s = generics.type_params_subst(self.db);
                                 t.substitution.clone().subst_bound_vars(&s)
                             }
                             TypeParamLoweringMode::Variable => t.substitution.clone(),
@@ -860,10 +853,9 @@ pub fn associated_type_shorthand_candidates<R>(
                 if generics.params.types[param_id.local_id].provenance
                     == TypeParamProvenance::TraitSelf
                 {
-                    let trait_ref = TraitRef {
-                        trait_id: to_chalk_trait_id(trait_id),
-                        substitution: Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST),
-                    };
+                    let trait_ref = TyBuilder::trait_ref(db, trait_id)
+                        .fill_with_bound_vars(DebruijnIndex::INNERMOST, 0)
+                        .build();
                     return search(trait_ref);
                 }
             }
@@ -972,7 +964,7 @@ pub(crate) fn trait_environment_query(
         // function default implementations (and hypothetical code
         // inside consts or type aliases)
         cov_mark::hit!(trait_self_implements_self);
-        let substs = Substitution::type_params(db, trait_id);
+        let substs = TyBuilder::type_params_subst(db, trait_id);
         let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
         let pred = WhereClause::Implemented(trait_ref);
         let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);
@@ -1061,7 +1053,7 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
 /// function body.
 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
     let generics = generics(db.upcast(), def.into());
-    let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
         substs.len(&Interner),
         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
@@ -1106,7 +1098,7 @@ fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<T
         return type_for_adt(db, def.into());
     }
     let generics = generics(db.upcast(), def.into());
-    let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
         substs.len(&Interner),
         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
@@ -1133,7 +1125,7 @@ fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -
         return type_for_adt(db, def.parent.into());
     }
     let generics = generics(db.upcast(), def.parent.into());
-    let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
         substs.len(&Interner),
         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
@@ -1141,9 +1133,10 @@ fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -
 }
 
 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
-    let generics = generics(db.upcast(), adt.into());
-    let substs = Substitution::bound_vars(&generics, DebruijnIndex::INNERMOST);
-    Binders::new(substs.len(&Interner), Ty::adt_ty(adt, substs))
+    let b = TyBuilder::adt(db, adt);
+    let num_binders = b.remaining();
+    let ty = b.fill_with_bound_vars(DebruijnIndex::INNERMOST, 0).build();
+    Binders::new(num_binders, ty)
 }
 
 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
@@ -1215,7 +1208,7 @@ impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for V
 /// namespace.
 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
     match def {
-        TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
+        TyDefId::BuiltinType(it) => Binders::new(0, TyBuilder::builtin(it)),
         TyDefId::AdtId(it) => type_for_adt(db, it),
         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
     }