10 files changed, 122 insertions, 129 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 a038674cf..8a3cc0283 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -12,7 +12,7 @@ use la_arena::ArenaMap;
 use crate::{
     method_resolution::{InherentImpls, TraitImpls},
     traits::chalk,
-    Binders, CallableDefId, FnDefId, GenericPredicate, InferenceResult, OpaqueTyId, PolyFnSig,
+    Binders, CallableDefId, FnDefId, GenericPredicate, ImplTraitId, InferenceResult, PolyFnSig,
     ReturnTypeImplTraits, TraitRef, Ty, TyDefId, ValueTyDefId,
 };
 use hir_expand::name::Name;
@@ -81,11 +81,11 @@ 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;
+    fn intern_impl_trait_id(&self, id: ImplTraitId) -> InternedOpaqueTyId;
     #[salsa::interned]
-    fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> ClosureId;
+    fn intern_closure(&self, id: (DefWithBodyId, ExprId)) -> InternedClosureId;
 
     #[salsa::invoke(chalk::associated_ty_data_query)]
     fn associated_ty_data(&self, id: chalk::AssocTypeId) -> Arc<chalk::AssociatedTyDatum>;
@@ -149,16 +149,16 @@ 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);
 impl_intern_key!(InternedOpaqueTyId);
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct ClosureId(salsa::InternId);
-impl_intern_key!(ClosureId);
+pub struct InternedClosureId(salsa::InternId);
+impl_intern_key!(InternedClosureId);
 
 /// This exists just for Chalk, because Chalk just has a single `FnDefId` where
 /// we have different IDs for struct and enum variant constructors.
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index b7e85e024..e6473586b 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, ImplTraitId, Interner, Lifetime, Obligation, OpaqueTy,
+    ProjectionTy, Scalar, Substs, TraitRef, Ty, TyKind,
 };
 
 pub struct HirFormatter<'a> {
@@ -313,22 +313,26 @@ impl HirDisplay for Ty {
                     )?;
                 }
 
+                // FIXME: all this just to decide whether to use parentheses...
                 let datas;
                 let predicates = match t.interned(&Interner) {
                     TyKind::Dyn(predicates) if predicates.len() > 1 => {
                         Cow::Borrowed(predicates.as_ref())
                     }
-                    &TyKind::Alias(AliasTy::Opaque(OpaqueTy {
-                        opaque_ty_id: OpaqueTyId::ReturnTypeImplTrait(func, idx),
-                        ref parameters,
-                    })) => {
-                        datas =
-                            f.db.return_type_impl_traits(func).expect("impl trait id without data");
-                        let data = (*datas)
-                            .as_ref()
-                            .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
-                        let bounds = data.subst(parameters);
-                        Cow::Owned(bounds.value)
+                    &TyKind::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id, ref parameters })) => {
+                        let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty_id.into());
+                        if let ImplTraitId::ReturnTypeImplTrait(func, idx) = impl_trait_id {
+                            datas =
+                                f.db.return_type_impl_traits(func)
+                                    .expect("impl trait id without data");
+                            let data = (*datas)
+                                .as_ref()
+                                .map(|rpit| rpit.impl_traits[idx as usize].bounds.clone());
+                            let bounds = data.subst(parameters);
+                            Cow::Owned(bounds.value)
+                        } else {
+                            Cow::Borrowed(&[][..])
+                        }
                     }
                     _ => Cow::Borrowed(&[][..]),
                 };
@@ -499,8 +503,9 @@ impl HirDisplay for Ty {
                 write!(f, "{}", type_alias.name)?;
             }
             TyKind::OpaqueType(opaque_ty_id, parameters) => {
-                match opaque_ty_id {
-                    &OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                let impl_trait_id = f.db.lookup_intern_impl_trait_id((*opaque_ty_id).into());
+                match impl_trait_id {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         let datas =
                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
                         let data = (*datas)
@@ -510,7 +515,7 @@ impl HirDisplay for Ty {
                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
                         // FIXME: it would maybe be good to distinguish this from the alias type (when debug printing), and to show the substitution
                     }
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "impl Future<Output = ")?;
                         parameters[0].hir_fmt(f)?;
                         write!(f, ">")?;
@@ -541,7 +546,8 @@ 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 +555,8 @@ 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<_>>(),
@@ -565,8 +571,9 @@ impl HirDisplay for Ty {
             }
             TyKind::Alias(AliasTy::Projection(p_ty)) => p_ty.hir_fmt(f)?,
             TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
-                match opaque_ty.opaque_ty_id {
-                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                let impl_trait_id = f.db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into());
+                match impl_trait_id {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         let datas =
                             f.db.return_type_impl_traits(func).expect("impl trait id without data");
                         let data = (*datas)
@@ -575,7 +582,7 @@ impl HirDisplay for Ty {
                         let bounds = data.subst(&opaque_ty.parameters);
                         write_bounds_like_dyn_trait_with_prefix("impl", &bounds.value, f)?;
                     }
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                         write!(f, "{{async block}}")?;
                     }
                 };
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/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 153f22f25..eee3e6ec5 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -21,8 +21,8 @@ use crate::{
     to_assoc_type_id,
     traits::{chalk::from_chalk, FnTrait, InEnvironment},
     utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Obligation, OpaqueTyId, Rawness,
-    Scalar, Substs, TraitRef, Ty, TyKind,
+    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Obligation, Rawness, Scalar, Substs,
+    TraitRef, Ty, TyKind,
 };
 
 use super::{
@@ -179,7 +179,8 @@ impl<'a> InferenceContext<'a> {
                 // Use the first type parameter as the output type of future.
                 // existenail type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
-                let opaque_ty_id = OpaqueTyId::AsyncBlockTypeImplTrait(self.owner, *body);
+                let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, *body);
+                let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
                 TyKind::OpaqueType(opaque_ty_id, Substs::single(inner_ty)).intern(&Interner)
             }
             Expr::Loop { body, label } => {
@@ -264,8 +265,9 @@ impl<'a> InferenceContext<'a> {
                     substs: Substs(sig_tys.clone().into()),
                 })
                 .intern(&Interner);
+                let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
                 let closure_ty =
-                    TyKind::Closure(self.owner, tgt_expr, Substs::single(sig_ty)).intern(&Interner);
+                    TyKind::Closure(closure_id, Substs::single(sig_ty)).intern(&Interner);
 
                 // Eagerly try to relate the closure type with the expected
                 // type, otherwise we often won't have enough information to
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 6b3485264..d6ff968f0 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -27,9 +27,8 @@ use std::{iter, mem, ops::Deref, sync::Arc};
 
 use base_db::salsa;
 use hir_def::{
-    builtin_type::BuiltinType, expr::ExprId, type_ref::Rawness, AssocContainerId, DefWithBodyId,
-    FunctionId, GenericDefId, HasModule, LifetimeParamId, Lookup, TraitId, TypeAliasId,
-    TypeParamId,
+    builtin_type::BuiltinType, expr::ExprId, type_ref::Rawness, AssocContainerId, FunctionId,
+    GenericDefId, HasModule, LifetimeParamId, Lookup, TraitId, TypeAliasId, TypeParamId,
 };
 use itertools::Itertools;
 
@@ -53,7 +52,10 @@ pub use crate::traits::chalk::Interner;
 
 pub type ForeignDefId = chalk_ir::ForeignDefId<Interner>;
 pub type AssocTypeId = chalk_ir::AssocTypeId<Interner>;
-pub(crate) type FnDefId = chalk_ir::FnDefId<Interner>;
+pub type FnDefId = chalk_ir::FnDefId<Interner>;
+pub type ClosureId = chalk_ir::ClosureId<Interner>;
+pub type OpaqueTyId = chalk_ir::OpaqueTyId<Interner>;
+pub type PlaceholderIndex = chalk_ir::PlaceholderIndex;
 
 #[derive(Clone, PartialEq, Eq, Debug, Hash)]
 pub enum Lifetime {
@@ -195,7 +197,7 @@ pub enum TyKind {
     ///
     /// The closure signature is stored in a `FnPtr` type in the first type
     /// parameter.
-    Closure(DefWithBodyId, ExprId, Substs),
+    Closure(ClosureId, Substs),
 
     /// Represents a foreign type declared in external blocks.
     ForeignType(ForeignDefId),
@@ -220,7 +222,7 @@ 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 +312,14 @@ 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 +327,7 @@ 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.
@@ -734,9 +739,7 @@ impl Ty {
                 ty_id == ty_id2
             }
             (TyKind::ForeignType(ty_id, ..), TyKind::ForeignType(ty_id2, ..)) => ty_id == ty_id2,
-            (TyKind::Closure(def, expr, _), TyKind::Closure(def2, expr2, _)) => {
-                expr == expr2 && def == def2
-            }
+            (TyKind::Closure(id1, _), TyKind::Closure(id2, _)) => id1 == id2,
             (TyKind::Ref(mutability, ..), TyKind::Ref(mutability2, ..))
             | (TyKind::Raw(mutability, ..), TyKind::Raw(mutability2, ..)) => {
                 mutability == mutability2
@@ -873,8 +876,8 @@ impl Ty {
     pub fn impl_trait_bounds(&self, db: &dyn HirDatabase) -> Option<Vec<GenericPredicate>> {
         match self.interned(&Interner) {
             TyKind::OpaqueType(opaque_ty_id, ..) => {
-                match opaque_ty_id {
-                    OpaqueTyId::AsyncBlockTypeImplTrait(def, _expr) => {
+                match db.lookup_intern_impl_trait_id((*opaque_ty_id).into()) {
+                    ImplTraitId::AsyncBlockTypeImplTrait(def, _expr) => {
                         let krate = def.module(db.upcast()).krate();
                         if let Some(future_trait) = db
                             .lang_item(krate, "future_trait".into())
@@ -892,12 +895,13 @@ impl Ty {
                             None
                         }
                     }
-                    OpaqueTyId::ReturnTypeImplTrait(..) => None,
+                    ImplTraitId::ReturnTypeImplTrait(..) => None,
                 }
             }
             TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
-                let predicates = match opaque_ty.opaque_ty_id {
-                    OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+                let predicates = match db.lookup_intern_impl_trait_id(opaque_ty.opaque_ty_id.into())
+                {
+                    ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                         db.return_type_impl_traits(func).map(|it| {
                             let data = (*it)
                                 .as_ref()
@@ -906,18 +910,19 @@ impl Ty {
                         })
                     }
                     // It always has an parameter for Future::Output type.
-                    OpaqueTyId::AsyncBlockTypeImplTrait(..) => unreachable!(),
+                    ImplTraitId::AsyncBlockTypeImplTrait(..) => unreachable!(),
                 };
 
                 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();
@@ -1120,7 +1125,7 @@ impl<T: TypeWalk> TypeWalk for Vec<T> {
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
-pub enum OpaqueTyId {
+pub enum ImplTraitId {
     ReturnTypeImplTrait(hir_def::FunctionId, u16),
     AsyncBlockTypeImplTrait(hir_def::DefWithBodyId, ExprId),
 }
@@ -1150,3 +1155,17 @@ 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..e57d5970f 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -27,14 +27,14 @@ 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,
         make_mut_slice, variant_data,
     },
     AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
-    OpaqueTy, OpaqueTyId, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
+    ImplTraitId, OpaqueTy, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
     ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
 };
 
@@ -228,14 +228,12 @@ impl Ty {
                             Some(GenericDefId::FunctionId(f)) => f,
                             _ => panic!("opaque impl trait lowering in non-function"),
                         };
-                        let impl_trait_id = OpaqueTyId::ReturnTypeImplTrait(func, idx);
+                        let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
+                        let opaque_ty_id = ctx.db.intern_impl_trait_id(impl_trait_id).into();
                         let generics = generics(ctx.db.upcast(), func.into());
                         let parameters = Substs::bound_vars(&generics, ctx.in_binders);
-                        TyKind::Alias(AliasTy::Opaque(OpaqueTy {
-                            opaque_ty_id: impl_trait_id,
-                            parameters,
-                        }))
-                        .intern(&Interner)
+                        TyKind::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id, parameters }))
+                            .intern(&Interner)
                     }
                     ImplTraitLoweringMode::Param => {
                         let idx = ctx.impl_trait_counter.get();
@@ -249,7 +247,9 @@ 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 +384,9 @@ 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 +398,7 @@ 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 +410,7 @@ 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 +691,9 @@ 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.rs b/crates/hir_ty/src/traits/chalk.rs
index bb92d8e2a..1f3e1c07a 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -177,10 +177,9 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
     }
 
     fn opaque_ty_data(&self, id: chalk_ir::OpaqueTyId<Interner>) -> Arc<OpaqueTyDatum> {
-        let interned_id = crate::db::InternedOpaqueTyId::from(id);
-        let full_id = self.db.lookup_intern_impl_trait_id(interned_id);
+        let full_id = self.db.lookup_intern_impl_trait_id(id.into());
         let bound = match full_id {
-            crate::OpaqueTyId::ReturnTypeImplTrait(func, idx) => {
+            crate::ImplTraitId::ReturnTypeImplTrait(func, idx) => {
                 let datas = self
                     .db
                     .return_type_impl_traits(func)
@@ -202,7 +201,7 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
                 let num_vars = datas.num_binders;
                 make_binders(bound, num_vars)
             }
-            crate::OpaqueTyId::AsyncBlockTypeImplTrait(..) => {
+            crate::ImplTraitId::AsyncBlockTypeImplTrait(..) => {
                 if let Some((future_trait, future_output)) = self
                     .db
                     .lang_item(self.krate, "future_trait".into())
@@ -716,14 +715,14 @@ impl From<crate::db::InternedOpaqueTyId> for OpaqueTyId {
     }
 }
 
-impl From<chalk_ir::ClosureId<Interner>> for crate::db::ClosureId {
+impl From<chalk_ir::ClosureId<Interner>> for crate::db::InternedClosureId {
     fn from(id: chalk_ir::ClosureId<Interner>) -> Self {
         Self::from_intern_id(id.0)
     }
 }
 
-impl From<crate::db::ClosureId> for chalk_ir::ClosureId<Interner> {
-    fn from(id: crate::db::ClosureId) -> Self {
+impl From<crate::db::InternedClosureId> for chalk_ir::ClosureId<Interner> {
+    fn from(id: crate::db::InternedClosureId) -> Self {
         chalk_ir::ClosureId(id.as_intern_id())
     }
 }
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 23ef07d77..2a66a2310 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;
@@ -18,7 +15,7 @@ use crate::{
     primitive::UintTy,
     traits::{Canonical, Obligation},
     AliasTy, CallableDefId, FnPointer, FnSig, GenericPredicate, InEnvironment, OpaqueTy,
-    OpaqueTyId, ProjectionPredicate, ProjectionTy, Scalar, Substs, TraitRef, Ty,
+    ProjectionPredicate, ProjectionTy, Scalar, Substs, TraitRef, Ty,
 };
 
 use super::interner::*;
@@ -44,8 +41,7 @@ impl ToChalk for Ty {
                 chalk_ir::TyKind::AssociatedType(assoc_type_id, substitution).intern(&Interner)
             }
 
-            TyKind::OpaqueType(impl_trait_id, substs) => {
-                let id = impl_trait_id.to_chalk(db);
+            TyKind::OpaqueType(id, substs) => {
                 let substitution = substs.to_chalk(db);
                 chalk_ir::TyKind::OpaqueType(id, substitution).intern(&Interner)
             }
@@ -72,10 +68,9 @@ impl ToChalk for Ty {
             }
             TyKind::Never => chalk_ir::TyKind::Never.intern(&Interner),
 
-            TyKind::Closure(def, expr, substs) => {
-                let closure_id = db.intern_closure((def, expr));
+            TyKind::Closure(closure_id, substs) => {
                 let substitution = substs.to_chalk(db);
-                chalk_ir::TyKind::Closure(closure_id.into(), substitution).intern(&Interner)
+                chalk_ir::TyKind::Closure(closure_id, substitution).intern(&Interner)
             }
 
             TyKind::Adt(adt_id, substs) => {
@@ -92,14 +87,7 @@ 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) => {
@@ -114,7 +102,7 @@ impl ToChalk for Ty {
                 chalk_ir::TyKind::Dyn(bounded_ty).intern(&Interner)
             }
             TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
-                let opaque_ty_id = opaque_ty.opaque_ty_id.to_chalk(db);
+                let opaque_ty_id = opaque_ty.opaque_ty_id;
                 let substitution = opaque_ty.parameters.to_chalk(db);
                 chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(chalk_ir::OpaqueTy {
                     opaque_ty_id,
@@ -129,22 +117,16 @@ 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);
                 TyKind::Alias(AliasTy::Projection(ProjectionTy { associated_ty, parameters }))
             }
             chalk_ir::TyKind::Alias(chalk_ir::AliasTy::Opaque(opaque_ty)) => {
-                let impl_trait_id = from_chalk(db, opaque_ty.opaque_ty_id);
+                let opaque_ty_id = opaque_ty.opaque_ty_id;
                 let parameters = from_chalk(db, opaque_ty.substitution);
-                TyKind::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id: impl_trait_id, parameters }))
+                TyKind::Alias(AliasTy::Opaque(OpaqueTy { opaque_ty_id, parameters }))
             }
             chalk_ir::TyKind::Function(chalk_ir::FnPointer {
                 num_binders,
@@ -182,7 +164,7 @@ impl ToChalk for Ty {
             }
 
             chalk_ir::TyKind::OpaqueType(opaque_type_id, subst) => {
-                TyKind::OpaqueType(from_chalk(db, opaque_type_id), from_chalk(db, subst))
+                TyKind::OpaqueType(opaque_type_id, from_chalk(db, subst))
             }
 
             chalk_ir::TyKind::Scalar(scalar) => TyKind::Scalar(scalar),
@@ -203,11 +185,7 @@ impl ToChalk for Ty {
                 TyKind::FnDef(fn_def_id, from_chalk(db, subst))
             }
 
-            chalk_ir::TyKind::Closure(id, subst) => {
-                let id: crate::db::ClosureId = id.into();
-                let (def, expr) = db.lookup_intern_closure(id);
-                TyKind::Closure(def, expr, from_chalk(db, subst))
-            }
+            chalk_ir::TyKind::Closure(id, subst) => TyKind::Closure(id, from_chalk(db, subst)),
 
             chalk_ir::TyKind::Foreign(foreign_def_id) => TyKind::ForeignType(foreign_def_id),
             chalk_ir::TyKind::Generator(_, _) => unimplemented!(), // FIXME
@@ -289,21 +267,6 @@ impl ToChalk for hir_def::TraitId {
     }
 }
 
-impl ToChalk for OpaqueTyId {
-    type Chalk = chalk_ir::OpaqueTyId<Interner>;
-
-    fn to_chalk(self, db: &dyn HirDatabase) -> chalk_ir::OpaqueTyId<Interner> {
-        db.intern_impl_trait_id(self).into()
-    }
-
-    fn from_chalk(
-        db: &dyn HirDatabase,
-        opaque_ty_id: chalk_ir::OpaqueTyId<Interner>,
-    ) -> OpaqueTyId {
-        db.lookup_intern_impl_trait_id(opaque_ty_id.into())
-    }
-}
-
 impl ToChalk for hir_def::ImplId {
     type Chalk = ImplId;