7 files changed, 42 insertions, 54 deletions

diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index eb82e1a11..39e0b328d 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -19,7 +19,7 @@ use crate::{
     db::HirDatabase, from_assoc_type_id, from_foreign_def_id, from_placeholder_idx, primitive,
     to_assoc_type_id, traits::chalk::from_chalk, utils::generics, AdtId, AliasEq, AliasTy,
     CallableDefId, CallableSig, DomainGoal, GenericArg, ImplTraitId, Interner, Lifetime, OpaqueTy,
-    ProjectionTy, QuantifiedWhereClause, Scalar, Substitution, TraitRef, Ty, TyExt, TyKind,
+    ProjectionTy, QuantifiedWhereClause, Scalar, TraitRef, Ty, TyExt, TyKind,
     WhereClause,
 };
 
@@ -592,7 +592,7 @@ impl HirDisplay for Ty {
                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
                     }
                     TypeParamProvenance::ArgumentImplTrait => {
-                        let substs = Substitution::type_params_for_generics(f.db, &generics);
+                        let substs = generics.type_params_subst(f.db);
                         let bounds = f
                             .db
                             .generic_predicates(id.parent)
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index caafeccb8..1b1d4458c 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -38,7 +38,7 @@ use syntax::SmolStr;
 
 use super::{
     traits::{DomainGoal, Guidance, Solution},
-    InEnvironment, ProjectionTy, Substitution, TraitEnvironment, TraitRef, Ty, TypeWalk,
+    InEnvironment, ProjectionTy, TraitEnvironment, TraitRef, Ty, TypeWalk,
 };
 use crate::{
     db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
@@ -487,7 +487,7 @@ impl<'a> InferenceContext<'a> {
             }
             TypeNs::SelfType(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substitution::type_params_for_generics(self.db, &generics);
+                let substs = generics.type_params_subst(self.db);
                 let ty = self.db.impl_self_ty(impl_id).subst(&substs);
                 match unresolved {
                     None => {
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index d55ae4900..671ea355f 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -80,7 +80,7 @@ impl<'a> InferenceContext<'a> {
             }
             ValueNs::ImplSelf(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substitution::type_params_for_generics(self.db, &generics);
+                let substs = generics.type_params_subst(self.db);
                 let ty = self.db.impl_self_ty(impl_id).subst(&substs);
                 if let Some((AdtId::StructId(struct_id), substs)) = ty.as_adt() {
                     let ty = self.db.value_ty(struct_id.into()).subst(&substs);
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index ebdcc4804..6d6443ca3 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -41,7 +41,7 @@ use hir_def::{
 use crate::{
     db::HirDatabase,
     display::HirDisplay,
-    utils::{generics, make_mut_slice, Generics},
+    utils::{generics, make_mut_slice},
 };
 
 pub use autoderef::autoderef;
@@ -464,33 +464,9 @@ impl Substitution {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn type_params_for_generics(
-        db: &dyn HirDatabase,
-        generic_params: &Generics,
-    ) -> Substitution {
-        Substitution::from_iter(
-            &Interner,
-            generic_params
-                .iter()
-                .map(|(id, _)| TyKind::Placeholder(to_placeholder_idx(db, id)).intern(&Interner)),
-        )
-    }
-
-    /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
     pub fn type_params(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substitution {
         let params = generics(db.upcast(), def.into());
-        Substitution::type_params_for_generics(db, &params)
-    }
-
-    /// Return Substs that replace each parameter by a bound variable.
-    pub(crate) fn bound_vars(generic_params: &Generics, debruijn: DebruijnIndex) -> Substitution {
-        Substitution::from_iter(
-            &Interner,
-            generic_params
-                .iter()
-                .enumerate()
-                .map(|(idx, _)| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner)),
-        )
+        params.type_params_subst(db)
     }
 }
 
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 644a2eed5..f9a721fdf 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -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)
             }
@@ -1060,7 +1052,7 @@ 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),
@@ -1105,7 +1097,7 @@ 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),
@@ -1132,7 +1124,7 @@ 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),
diff --git a/crates/hir_ty/src/traits/chalk.rs b/crates/hir_ty/src/traits/chalk.rs
index 36a397990..541e6082f 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -387,7 +387,7 @@ pub(crate) fn associated_ty_data_query(
     // Lower bounds -- we could/should maybe move this to a separate query in `lower`
     let type_alias_data = db.type_alias_data(type_alias);
     let generic_params = generics(db.upcast(), type_alias.into());
-    let bound_vars = Substitution::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let bound_vars = generic_params.bound_vars_subst(DebruijnIndex::INNERMOST);
     let resolver = hir_def::resolver::HasResolver::resolver(type_alias, db.upcast());
     let ctx = crate::TyLoweringContext::new(db, &resolver)
         .with_type_param_mode(crate::lower::TypeParamLoweringMode::Variable);
@@ -421,7 +421,7 @@ pub(crate) fn trait_datum_query(
     let trait_data = db.trait_data(trait_);
     debug!("trait {:?} = {:?}", trait_id, trait_data.name);
     let generic_params = generics(db.upcast(), trait_.into());
-    let bound_vars = Substitution::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let bound_vars = generic_params.bound_vars_subst(DebruijnIndex::INNERMOST);
     let flags = rust_ir::TraitFlags {
         auto: trait_data.is_auto,
         upstream: trait_.lookup(db.upcast()).container.krate() != krate,
@@ -490,7 +490,7 @@ pub(crate) fn struct_datum_query(
     let upstream = adt_id.module(db.upcast()).krate() != krate;
     let where_clauses = {
         let generic_params = generics(db.upcast(), adt_id.into());
-        let bound_vars = Substitution::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+        let bound_vars = generic_params.bound_vars_subst(DebruijnIndex::INNERMOST);
         convert_where_clauses(db, adt_id.into(), &bound_vars)
     };
     let flags = rust_ir::AdtFlags {
@@ -539,7 +539,7 @@ fn impl_def_datum(
     let impl_data = db.impl_data(impl_id);
 
     let generic_params = generics(db.upcast(), impl_id.into());
-    let bound_vars = Substitution::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let bound_vars = generic_params.bound_vars_subst(DebruijnIndex::INNERMOST);
     let trait_ = trait_ref.hir_trait_id();
     let impl_type = if impl_id.lookup(db.upcast()).container.krate() == krate {
         rust_ir::ImplType::Local
@@ -629,7 +629,7 @@ pub(crate) fn fn_def_datum_query(
     let callable_def: CallableDefId = from_chalk(db, fn_def_id);
     let generic_params = generics(db.upcast(), callable_def.into());
     let sig = db.callable_item_signature(callable_def);
-    let bound_vars = Substitution::bound_vars(&generic_params, DebruijnIndex::INNERMOST);
+    let bound_vars = generic_params.bound_vars_subst(DebruijnIndex::INNERMOST);
     let where_clauses = convert_where_clauses(db, callable_def.into(), &bound_vars);
     let bound = rust_ir::FnDefDatumBound {
         // Note: Chalk doesn't actually use this information yet as far as I am aware, but we provide it anyway
diff --git a/crates/hir_ty/src/utils.rs b/crates/hir_ty/src/utils.rs
index 42d7af146..b23e91b1b 100644
--- a/crates/hir_ty/src/utils.rs
+++ b/crates/hir_ty/src/utils.rs
@@ -2,7 +2,7 @@
 //! query, but can't be computed directly from `*Data` (ie, which need a `db`).
 use std::sync::Arc;
 
-use chalk_ir::DebruijnIndex;
+use chalk_ir::{BoundVar, DebruijnIndex};
 use hir_def::{
     adt::VariantData,
     db::DefDatabase,
@@ -16,7 +16,7 @@ use hir_def::{
 };
 use hir_expand::name::{name, Name};
 
-use crate::{db::HirDatabase, TraitRef, TypeWalk, WhereClause};
+use crate::{db::HirDatabase, Interner, Substitution, TraitRef, TyKind, TypeWalk, WhereClause};
 
 fn direct_super_traits(db: &dyn DefDatabase, trait_: TraitId) -> Vec<TraitId> {
     let resolver = trait_.resolver(db);
@@ -249,6 +249,26 @@ impl Generics {
             self.parent_generics.as_ref().and_then(|g| g.find_param(param))
         }
     }
+
+    /// Returns a Substitution that replaces each parameter by a bound variable.
+    pub(crate) fn bound_vars_subst(&self, debruijn: DebruijnIndex) -> Substitution {
+        Substitution::from_iter(
+            &Interner,
+            self.iter()
+                .enumerate()
+                .map(|(idx, _)| TyKind::BoundVar(BoundVar::new(debruijn, idx)).intern(&Interner)),
+        )
+    }
+
+    /// Returns a Substitution that replaces each parameter by itself (i.e. `Ty::Param`).
+    pub(crate) fn type_params_subst(&self, db: &dyn HirDatabase) -> Substitution {
+        Substitution::from_iter(
+            &Interner,
+            self.iter().map(|(id, _)| {
+                TyKind::Placeholder(crate::to_placeholder_idx(db, id)).intern(&Interner)
+            }),
+        )
+    }
 }
 
 fn parent_generic_def(db: &dyn DefDatabase, def: GenericDefId) -> Option<GenericDefId> {