8 files changed, 34 insertions, 27 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 817a01db1..04875240b 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1825,7 +1825,7 @@ impl Type {
             Solution::Unique(s) => s
                 .value
                 .subst
-                .interned()
+                .as_slice(&Interner)
                 .first()
                 .map(|ty| self.derived(ty.assert_ty_ref(&Interner).clone())),
             Solution::Ambig(_) => None,
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index d7a3977e5..92224b46b 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -265,7 +265,7 @@ impl HirDisplay for ProjectionTy {
         write!(f, " as {}", trait_.name)?;
         if self.substitution.len(&Interner) > 1 {
             write!(f, "<")?;
-            f.write_joined(&self.substitution.interned()[1..], ", ")?;
+            f.write_joined(&self.substitution.as_slice(&Interner)[1..], ", ")?;
             write!(f, ">")?;
         }
         write!(f, ">::{}", f.db.type_alias_data(from_assoc_type_id(self.associated_ty_id)).name)?;
@@ -416,7 +416,7 @@ impl HirDisplay for Ty {
                     write!(f, ",)")?;
                 } else {
                     write!(f, "(")?;
-                    f.write_joined(&*substs.interned(), ", ")?;
+                    f.write_joined(&*substs.as_slice(&Interner), ", ")?;
                     write!(f, ")")?;
                 }
             }
@@ -444,7 +444,7 @@ impl HirDisplay for Ty {
                     // We print all params except implicit impl Trait params. Still a bit weird; should we leave out parent and self?
                     if total_len > 0 {
                         write!(f, "<")?;
-                        f.write_joined(&parameters.interned()[..total_len], ", ")?;
+                        f.write_joined(&parameters.as_slice(&Interner)[..total_len], ", ")?;
                         write!(f, ">")?;
                     }
                 }
@@ -491,7 +491,7 @@ impl HirDisplay for Ty {
                             .map(|generic_def_id| f.db.generic_defaults(generic_def_id))
                             .filter(|defaults| !defaults.is_empty())
                         {
-                            None => parameters.interned().as_ref(),
+                            None => parameters.as_slice(&Interner),
                             Some(default_parameters) => {
                                 let mut default_from = 0;
                                 for (i, parameter) in parameters.iter(&Interner).enumerate() {
@@ -515,11 +515,11 @@ impl HirDisplay for Ty {
                                         }
                                     }
                                 }
-                                &parameters.interned()[0..default_from]
+                                &parameters.as_slice(&Interner)[0..default_from]
                             }
                         }
                     } else {
-                        parameters.interned().as_ref()
+                        parameters.as_slice(&Interner)
                     };
                     if !parameters_to_write.is_empty() {
                         write!(f, "<")?;
@@ -542,7 +542,7 @@ impl HirDisplay for Ty {
                     write!(f, "{}::{}", trait_.name, type_alias_data.name)?;
                     if parameters.len(&Interner) > 0 {
                         write!(f, "<")?;
-                        f.write_joined(&*parameters.interned(), ", ")?;
+                        f.write_joined(&*parameters.as_slice(&Interner), ", ")?;
                         write!(f, ">")?;
                     }
                 } else {
@@ -749,13 +749,13 @@ fn write_bounds_like_dyn_trait(
                 // existential) here, which is the only thing that's
                 // possible in actual Rust, and hence don't print it
                 write!(f, "{}", f.db.trait_data(trait_).name)?;
-                if let [_, params @ ..] = &*trait_ref.substitution.interned().as_slice() {
+                if let [_, params @ ..] = &*trait_ref.substitution.as_slice(&Interner) {
                     if is_fn_trait {
                         if let Some(args) =
                             params.first().and_then(|it| it.assert_ty_ref(&Interner).as_tuple())
                         {
                             write!(f, "(")?;
-                            f.write_joined(&*args.interned(), ", ")?;
+                            f.write_joined(args.as_slice(&Interner), ", ")?;
                             write!(f, ")")?;
                         }
                     } else if !params.is_empty() {
@@ -814,7 +814,7 @@ fn fmt_trait_ref(tr: &TraitRef, f: &mut HirFormatter, use_as: bool) -> Result<()
     write!(f, "{}", f.db.trait_data(tr.hir_trait_id()).name)?;
     if tr.substitution.len(&Interner) > 1 {
         write!(f, "<")?;
-        f.write_joined(&tr.substitution.interned()[1..], ", ")?;
+        f.write_joined(&tr.substitution.as_slice(&Interner)[1..], ", ")?;
         write!(f, ">")?;
     }
     Ok(())
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index cbbfa8b5c..ee6763926 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -462,7 +462,7 @@ impl<'a> InferenceContext<'a> {
                     };
                     match canonicalized.decanonicalize_ty(derefed_ty.value).kind(&Interner) {
                         TyKind::Tuple(_, substs) => name.as_tuple_index().and_then(|idx| {
-                            substs.interned().get(idx).map(|a| a.assert_ty_ref(&Interner)).cloned()
+                            substs.as_slice(&Interner).get(idx).map(|a| a.assert_ty_ref(&Interner)).cloned()
                         }),
                         TyKind::Adt(AdtId(hir_def::AdtId::StructId(s)), parameters) => {
                             let local_id = self.db.struct_data(*s).variant_data.field(name)?;
diff --git a/crates/hir_ty/src/infer/pat.rs b/crates/hir_ty/src/infer/pat.rs
index a41e8e116..aea354cde 100644
--- a/crates/hir_ty/src/infer/pat.rs
+++ b/crates/hir_ty/src/infer/pat.rs
@@ -122,7 +122,7 @@ impl<'a> InferenceContext<'a> {
         let ty = match &body[pat] {
             &Pat::Tuple { ref args, ellipsis } => {
                 let expectations = match expected.as_tuple() {
-                    Some(parameters) => &*parameters.interned().as_slice(),
+                    Some(parameters) => &*parameters.as_slice(&Interner),
                     _ => &[],
                 };
 
@@ -242,7 +242,7 @@ impl<'a> InferenceContext<'a> {
                     let (inner_ty, alloc_ty) = match expected.as_adt() {
                         Some((adt, subst)) if adt == box_adt => (
                             subst.at(&Interner, 0).assert_ty_ref(&Interner).clone(),
-                            subst.interned().get(1).and_then(|a| a.ty(&Interner).cloned()),
+                            subst.as_slice(&Interner).get(1).and_then(|a| a.ty(&Interner).cloned()),
                         ),
                         _ => (self.result.standard_types.unknown.clone(), None),
                     };
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index f8955aa32..495282eba 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -101,7 +101,7 @@ impl<'a> InferenceContext<'a> {
         let substs = ctx.substs_from_path(path, typable, true);
         let ty = TyBuilder::value_ty(self.db, typable)
             .use_parent_substs(&parent_substs)
-            .fill(substs.interned()[parent_substs.len(&Interner)..].iter().cloned())
+            .fill(substs.as_slice(&Interner)[parent_substs.len(&Interner)..].iter().cloned())
             .build();
         Some(ty)
     }
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 874c95411..beb58d711 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -109,7 +109,7 @@ pub type WhereClause = chalk_ir::WhereClause<Interner>;
 pub fn subst_prefix(s: &Substitution, n: usize) -> Substitution {
     Substitution::from_iter(
         &Interner,
-        s.interned()[..std::cmp::min(s.len(&Interner), n)].iter().cloned(),
+        s.as_slice(&Interner)[..std::cmp::min(s.len(&Interner), n)].iter().cloned(),
     )
 }
 
@@ -187,7 +187,7 @@ impl CallableSig {
                 .shifted_out_to(&Interner, DebruijnIndex::ONE)
                 .expect("unexpected lifetime vars in fn ptr")
                 .0
-                .interned()
+                .as_slice(&Interner)
                 .iter()
                 .map(|arg| arg.assert_ty_ref(&Interner).clone())
                 .collect(),
diff --git a/crates/hir_ty/src/traits/chalk/interner.rs b/crates/hir_ty/src/traits/chalk/interner.rs
index 7a3bd41d4..17e056f03 100644
--- a/crates/hir_ty/src/traits/chalk/interner.rs
+++ b/crates/hir_ty/src/traits/chalk/interner.rs
@@ -3,11 +3,12 @@
 
 use super::tls;
 use base_db::salsa::InternId;
-use chalk_ir::{GenericArg, Goal, GoalData};
+use chalk_ir::{Goal, GoalData};
 use hir_def::{
     intern::{impl_internable, InternStorage, Internable, Interned},
     TypeAliasId,
 };
+use crate::GenericArg;
 use smallvec::SmallVec;
 use std::{fmt, sync::Arc};
 
@@ -32,7 +33,13 @@ pub(crate) type Variances = chalk_ir::Variances<Interner>;
 #[derive(PartialEq, Eq, Hash, Debug)]
 pub struct InternedVariableKindsInner(Vec<chalk_ir::VariableKind<Interner>>);
 
-impl_internable!(InternedVariableKindsInner,);
+#[derive(PartialEq, Eq, Hash, Debug)]
+pub struct InternedSubstitutionInner(SmallVec<[GenericArg; 2]>);
+
+impl_internable!(
+    InternedVariableKindsInner,
+    InternedSubstitutionInner,
+);
 
 impl chalk_ir::interner::Interner for Interner {
     type InternedType = Arc<chalk_ir::TyData<Self>>;
@@ -42,7 +49,7 @@ impl chalk_ir::interner::Interner for Interner {
     type InternedGenericArg = chalk_ir::GenericArgData<Self>;
     type InternedGoal = Arc<GoalData<Self>>;
     type InternedGoals = Vec<Goal<Self>>;
-    type InternedSubstitution = SmallVec<[GenericArg<Self>; 2]>;
+    type InternedSubstitution = Interned<InternedSubstitutionInner>;
     type InternedProgramClause = Arc<chalk_ir::ProgramClauseData<Self>>;
     type InternedProgramClauses = Arc<[chalk_ir::ProgramClause<Self>]>;
     type InternedQuantifiedWhereClauses = Vec<chalk_ir::QuantifiedWhereClause<Self>>;
@@ -107,7 +114,7 @@ impl chalk_ir::interner::Interner for Interner {
     }
 
     fn debug_generic_arg(
-        parameter: &GenericArg<Interner>,
+        parameter: &GenericArg,
         fmt: &mut fmt::Formatter<'_>,
     ) -> Option<fmt::Result> {
         tls::with_current_program(|prog| Some(prog?.debug_generic_arg(parameter, fmt)))
@@ -272,16 +279,16 @@ impl chalk_ir::interner::Interner for Interner {
 
     fn intern_substitution<E>(
         &self,
-        data: impl IntoIterator<Item = Result<GenericArg<Self>, E>>,
+        data: impl IntoIterator<Item = Result<GenericArg, E>>,
     ) -> Result<Self::InternedSubstitution, E> {
-        data.into_iter().collect()
+        Ok(Interned::new(InternedSubstitutionInner(data.into_iter().collect::<Result<SmallVec<_>, _>>()?)))
     }
 
     fn substitution_data<'a>(
         &self,
         substitution: &'a Self::InternedSubstitution,
-    ) -> &'a [GenericArg<Self>] {
-        substitution
+    ) -> &'a [GenericArg] {
+        &substitution.as_ref().0
     }
 
     fn intern_program_clause(
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 7818f6387..e78581ea5 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -99,7 +99,7 @@ pub(super) fn generic_predicate_to_inline_bound(
                 // have the expected self type
                 return None;
             }
-            let args_no_self = trait_ref.substitution.interned()[1..]
+            let args_no_self = trait_ref.substitution.as_slice(&Interner)[1..]
                 .iter()
                 .map(|ty| ty.clone().cast(&Interner))
                 .collect();
@@ -111,7 +111,7 @@ pub(super) fn generic_predicate_to_inline_bound(
                 return None;
             }
             let trait_ = projection_ty.trait_(db);
-            let args_no_self = projection_ty.substitution.interned()[1..]
+            let args_no_self = projection_ty.substitution.as_slice(&Interner)[1..]
                 .iter()
                 .map(|ty| ty.clone().cast(&Interner))
                 .collect();