8 files changed, 53 insertions, 44 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 7f8f936d3..571b89bc3 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1384,7 +1384,7 @@ impl TypeParam {
     pub fn ty(self, db: &dyn HirDatabase) -> Type {
         let resolver = self.id.parent.resolver(db.upcast());
         let krate = self.id.parent.module(db.upcast()).krate();
-        let ty = TyKind::Placeholder(self.id).intern(&Interner);
+        let ty = TyKind::Placeholder(hir_ty::to_placeholder_idx(db, self.id)).intern(&Interner);
         Type::new_with_resolver_inner(db, krate, &resolver, ty)
     }
 
diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 1b59616ba..c198f6903 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -81,7 +81,7 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::interned]
     fn intern_callable_def(&self, callable_def: CallableDefId) -> InternedCallableDefId;
     #[salsa::interned]
-    fn intern_type_param_id(&self, param_id: TypeParamId) -> GlobalTypeParamId;
+    fn intern_type_param_id(&self, param_id: TypeParamId) -> InternedTypeParamId;
     #[salsa::interned]
     fn intern_impl_trait_id(&self, id: OpaqueTyId) -> InternedOpaqueTyId;
     #[salsa::interned]
@@ -149,8 +149,8 @@ fn hir_database_is_object_safe() {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct GlobalTypeParamId(salsa::InternId);
-impl_intern_key!(GlobalTypeParamId);
+pub struct InternedTypeParamId(salsa::InternId);
+impl_intern_key!(InternedTypeParamId);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct InternedOpaqueTyId(salsa::InternId);
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index b7e85e024..0a13c8636 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -11,10 +11,10 @@ use hir_def::{
 use hir_expand::name::Name;
 
 use crate::{
-    db::HirDatabase, from_assoc_type_id, from_foreign_def_id, primitive, to_assoc_type_id,
-    traits::chalk::from_chalk, utils::generics, AdtId, AliasTy, CallableDefId, CallableSig,
-    GenericPredicate, Interner, Lifetime, Obligation, OpaqueTy, OpaqueTyId, ProjectionTy, Scalar,
-    Substs, TraitRef, Ty, TyKind,
+    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, AliasTy, CallableDefId,
+    CallableSig, GenericPredicate, Interner, Lifetime, Obligation, OpaqueTy, OpaqueTyId,
+    ProjectionTy, Scalar, Substs, TraitRef, Ty, TyKind,
 };
 
 pub struct HirFormatter<'a> {
@@ -541,7 +541,8 @@ impl HirDisplay for Ty {
                     write!(f, "{{closure}}")?;
                 }
             }
-            TyKind::Placeholder(id) => {
+            TyKind::Placeholder(idx) => {
+                let id = from_placeholder_idx(f.db, *idx);
                 let generics = generics(f.db.upcast(), id.parent);
                 let param_data = &generics.params.types[id.local_id];
                 match param_data.provenance {
@@ -549,8 +550,8 @@ impl HirDisplay for Ty {
                         write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
                     }
                     TypeParamProvenance::ArgumentImplTrait => {
-                        let bounds = f.db.generic_predicates_for_param(*id);
-                        let substs = Substs::type_params_for_generics(&generics);
+                        let bounds = f.db.generic_predicates_for_param(id);
+                        let substs = Substs::type_params_for_generics(f.db, &generics);
                         write_bounds_like_dyn_trait_with_prefix(
                             "impl",
                             &bounds.iter().map(|b| b.clone().subst(&substs)).collect::<Vec<_>>(),
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 9d9bf549c..4f7463422 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -454,7 +454,7 @@ impl<'a> InferenceContext<'a> {
             }
             TypeNs::SelfType(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substs::type_params_for_generics(&generics);
+                let substs = Substs::type_params_for_generics(self.db, &generics);
                 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 392952178..c6681834c 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -79,7 +79,7 @@ impl<'a> InferenceContext<'a> {
             }
             ValueNs::ImplSelf(impl_id) => {
                 let generics = crate::utils::generics(self.db.upcast(), impl_id.into());
-                let substs = Substs::type_params_for_generics(&generics);
+                let substs = Substs::type_params_for_generics(self.db, &generics);
                 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 ec2010e4b..d1c018283 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -54,6 +54,7 @@ pub type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
 pub type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
 pub type FnDefId = chalk_ir::FnDefId<Interner>;
 pub type ClosureId = chalk_ir::ClosureId<Interner>;
+pub type PlaceholderIndex = chalk_ir::PlaceholderIndex;
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum Lifetime {
@@ -220,7 +221,7 @@ pub enum TyKind {
     /// {}` when we're type-checking the body of that function. In this
     /// situation, we know this stands for *some* type, but don't know the exact
     /// type.
-    Placeholder(TypeParamId),
+    Placeholder(PlaceholderIndex),
 
     /// A bound type variable. This is used in various places: when representing
     /// some polymorphic type like the type of function `fn f<T>`, the type
@@ -310,11 +311,14 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs {
+    pub(crate) fn type_params_for_generics(
+        db: &dyn HirDatabase,
+        generic_params: &Generics,
+    ) -> Substs {
         Substs(
             generic_params
                 .iter()
-                .map(|(id, _)| TyKind::Placeholder(id).intern(&Interner))
+                .map(|(id, _)| TyKind::Placeholder(to_placeholder_idx(db, id)).intern(&Interner))
                 .collect(),
         )
     }
@@ -322,7 +326,7 @@ impl Substs {
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
     pub fn type_params(db: &dyn HirDatabase, def: impl Into<GenericDefId>) -> Substs {
         let params = generics(db.upcast(), def.into());
-        Substs::type_params_for_generics(&params)
+        Substs::type_params_for_generics(db, &params)
     }
 
     /// Return Substs that replace each parameter by a bound variable.
@@ -909,13 +913,14 @@ impl Ty {
 
                 predicates.map(|it| it.value)
             }
-            TyKind::Placeholder(id) => {
+            TyKind::Placeholder(idx) => {
+                let id = from_placeholder_idx(db, *idx);
                 let generic_params = db.generic_params(id.parent);
                 let param_data = &generic_params.types[id.local_id];
                 match param_data.provenance {
                     hir_def::generics::TypeParamProvenance::ArgumentImplTrait => {
                         let predicates = db
-                            .generic_predicates_for_param(*id)
+                            .generic_predicates_for_param(id)
                             .into_iter()
                             .map(|pred| pred.value.clone())
                             .collect_vec();
@@ -1148,3 +1153,17 @@ pub fn to_assoc_type_id(id: TypeAliasId) -> AssocTypeId {
 pub fn from_assoc_type_id(id: AssocTypeId) -> TypeAliasId {
     salsa::InternKey::from_intern_id(id.0)
 }
+
+pub fn from_placeholder_idx(db: &dyn HirDatabase, idx: PlaceholderIndex) -> TypeParamId {
+    assert_eq!(idx.ui, chalk_ir::UniverseIndex::ROOT);
+    let interned_id = salsa::InternKey::from_intern_id(salsa::InternId::from(idx.idx));
+    db.lookup_intern_type_param_id(interned_id)
+}
+
+pub fn to_placeholder_idx(db: &dyn HirDatabase, id: TypeParamId) -> PlaceholderIndex {
+    let interned_id = db.intern_type_param_id(id);
+    PlaceholderIndex {
+        ui: chalk_ir::UniverseIndex::ROOT,
+        idx: salsa::InternKey::as_intern_id(&interned_id).as_usize(),
+    }
+}
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index b8b1400eb..78a914cac 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -27,7 +27,7 @@ use stdx::impl_from;
 
 use crate::{
     db::HirDatabase,
-    to_assoc_type_id,
+    to_assoc_type_id, to_placeholder_idx,
     traits::chalk::{Interner, ToChalk},
     utils::{
         all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
@@ -249,7 +249,9 @@ impl Ty {
                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
                                 })
                                 .nth(idx as usize)
-                                .map_or(TyKind::Unknown, |(id, _)| TyKind::Placeholder(id));
+                                .map_or(TyKind::Unknown, |(id, _)| {
+                                    TyKind::Placeholder(to_placeholder_idx(ctx.db, id))
+                                });
                             param.intern(&Interner)
                         } else {
                             TyKind::Unknown.intern(&Interner)
@@ -384,7 +386,9 @@ impl Ty {
                     ctx.resolver.generic_def().expect("generics in scope"),
                 );
                 match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => TyKind::Placeholder(param_id),
+                    TypeParamLoweringMode::Placeholder => {
+                        TyKind::Placeholder(to_placeholder_idx(ctx.db, param_id))
+                    }
                     TypeParamLoweringMode::Variable => {
                         let idx = generics.param_idx(param_id).expect("matching generics");
                         TyKind::BoundVar(BoundVar::new(ctx.in_binders, idx))
@@ -396,7 +400,7 @@ impl Ty {
                 let generics = generics(ctx.db.upcast(), impl_id.into());
                 let substs = match ctx.type_param_mode {
                     TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(&generics)
+                        Substs::type_params_for_generics(ctx.db, &generics)
                     }
                     TypeParamLoweringMode::Variable => {
                         Substs::bound_vars(&generics, ctx.in_binders)
@@ -408,7 +412,7 @@ impl Ty {
                 let generics = generics(ctx.db.upcast(), adt.into());
                 let substs = match ctx.type_param_mode {
                     TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(&generics)
+                        Substs::type_params_for_generics(ctx.db, &generics)
                     }
                     TypeParamLoweringMode::Variable => {
                         Substs::bound_vars(&generics, ctx.in_binders)
@@ -689,8 +693,9 @@ impl GenericPredicate {
                         let generics = generics(ctx.db.upcast(), generic_def);
                         let param_id =
                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
+                        let placeholder = to_placeholder_idx(ctx.db, param_id);
                         match ctx.type_param_mode {
-                            TypeParamLoweringMode::Placeholder => TyKind::Placeholder(param_id),
+                            TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
                             TypeParamLoweringMode::Variable => {
                                 let idx = generics.param_idx(param_id).expect("matching generics");
                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 56a30363b..460955756 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -3,10 +3,7 @@
 //! Chalk (in both directions); plus some helper functions for more specialized
 //! conversions.
 
-use chalk_ir::{
-    cast::Cast, fold::shift::Shift, interner::HasInterner, LifetimeData, PlaceholderIndex,
-    UniverseIndex,
-};
+use chalk_ir::{cast::Cast, fold::shift::Shift, interner::HasInterner, LifetimeData};
 use chalk_solve::rust_ir;
 
 use base_db::salsa::InternKey;
@@ -91,14 +88,7 @@ impl ToChalk for Ty {
                 .cast(&Interner)
                 .intern(&Interner)
             }
-            TyKind::Placeholder(id) => {
-                let interned_id = db.intern_type_param_id(id);
-                PlaceholderIndex {
-                    ui: UniverseIndex::ROOT,
-                    idx: interned_id.as_intern_id().as_usize(),
-                }
-                .to_ty::<Interner>(&Interner)
-            }
+            TyKind::Placeholder(idx) => idx.to_ty::<Interner>(&Interner),
             TyKind::BoundVar(idx) => chalk_ir::TyKind::BoundVar(idx).intern(&Interner),
             TyKind::InferenceVar(..) => panic!("uncanonicalized infer ty"),
             TyKind::Dyn(predicates) => {
@@ -128,13 +118,7 @@ impl ToChalk for Ty {
         match chalk.data(&Interner).kind.clone() {
             chalk_ir::TyKind::Error => TyKind::Unknown,
             chalk_ir::TyKind::Array(ty, _size) => TyKind::Array(Substs::single(from_chalk(db, ty))),
-            chalk_ir::TyKind::Placeholder(idx) => {
-                assert_eq!(idx.ui, UniverseIndex::ROOT);
-                let interned_id = crate::db::GlobalTypeParamId::from_intern_id(
-                    crate::salsa::InternId::from(idx.idx),
-                );
-                TyKind::Placeholder(db.lookup_intern_type_param_id(interned_id))
-            }
+            chalk_ir::TyKind::Placeholder(idx) => TyKind::Placeholder(idx),
             chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Projection(proj)) => {
                 let associated_ty = proj.associated_ty_id;
                 let parameters = from_chalk(db, proj.substitution);