4 files changed, 17 insertions, 14 deletions

diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 56a9365cb..82ab9c5fe 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -180,7 +180,8 @@ impl<'a> InferenceContext<'a> {
                 let inner_ty = self.infer_expr(*body, &Expectation::none());
                 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, Substitution::single(inner_ty)).intern(&Interner)
+                TyKind::OpaqueType(opaque_ty_id, Substitution::from1(&Interner, inner_ty))
+                    .intern(&Interner)
             }
             Expr::Loop { body, label } => {
                 self.breakables.push(BreakableContext {
@@ -266,7 +267,8 @@ impl<'a> InferenceContext<'a> {
                 .intern(&Interner);
                 let closure_id = self.db.intern_closure((self.owner, tgt_expr)).into();
                 let closure_ty =
-                    TyKind::Closure(closure_id, Substitution::single(sig_ty)).intern(&Interner);
+                    TyKind::Closure(closure_id, Substitution::from1(&Interner, 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/lib.rs b/crates/hir_ty/src/lib.rs
index 928dd76e5..6d5123cf1 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -31,7 +31,6 @@ mod test_db;
 use std::sync::Arc;
 
 use itertools::Itertools;
-use smallvec::SmallVec;
 
 use base_db::salsa;
 use hir_def::{
@@ -77,14 +76,6 @@ pub type ChalkTraitId = chalk_ir::TraitId<Interner>;
 pub type FnSig = chalk_ir::FnSig<Interner>;
 
 impl Substitution {
-    pub fn single(ty: Ty) -> Substitution {
-        Substitution::intern({
-            let mut v = SmallVec::new();
-            v.push(ty.cast(&Interner));
-            v
-        })
-    }
-
     pub fn prefix(&self, n: usize) -> Substitution {
         Substitution::intern(self.interned()[..std::cmp::min(self.len(&Interner), n)].into())
     }
diff --git a/crates/hir_ty/src/traits/chalk.rs b/crates/hir_ty/src/traits/chalk.rs
index dff87ef70..075e82f4b 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -220,7 +220,8 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
                     let impl_bound = WhereClause::Implemented(TraitRef {
                         trait_id: to_chalk_trait_id(future_trait),
                         // Self type as the first parameter.
-                        substitution: Substitution::single(
+                        substitution: Substitution::from1(
+                            &Interner,
                             TyKind::BoundVar(BoundVar {
                                 debruijn: DebruijnIndex::INNERMOST,
                                 index: 0,
@@ -232,7 +233,8 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
                         alias: AliasTy::Projection(ProjectionTy {
                             associated_ty_id: to_assoc_type_id(future_output),
                             // Self type as the first parameter.
-                            substitution: Substitution::single(
+                            substitution: Substitution::from1(
+                                &Interner,
                                 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
                                     .intern(&Interner),
                             ),
diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index bd89991dc..6dffda1ca 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -4,7 +4,7 @@
 use std::sync::Arc;
 
 use chalk_ir::{
-    cast::{CastTo, Caster},
+    cast::{Cast, CastTo, Caster},
     BoundVar, Mutability, Scalar, TyVariableKind,
 };
 use smallvec::SmallVec;
@@ -278,6 +278,14 @@ impl Substitution {
         self.0.iter()
     }
 
+    pub fn from1(_interner: &Interner, ty: Ty) -> Substitution {
+        Substitution::intern({
+            let mut v = SmallVec::new();
+            v.push(ty.cast(&Interner));
+            v
+        })
+    }
+
     pub fn from_iter(
         interner: &Interner,
         elements: impl IntoIterator<Item = impl CastTo<GenericArg>>,