Fix return type of Substitution::interned

Author: flodiebold

crates/hir_ty/src/display.rs

@@ -745,7 +745,7 @@ 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() {
+                if let [_, params @ ..] = &*trait_ref.substitution.interned().as_slice() {
                     if is_fn_trait {
                         if let Some(args) =
                             params.first().and_then(|it| it.assert_ty_ref(&Interner).as_tuple())

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(),
+                    Some(parameters) => &*parameters.interned().as_slice(),
                     _ => &[],
                 };
 

crates/hir_ty/src/types.rs

@@ -282,7 +282,7 @@ impl GenericArg {
 pub struct Substitution(SmallVec<[GenericArg; 2]>);
 
 impl Substitution {
-    pub fn interned(&self) -> &[GenericArg] {
+    pub fn interned(&self) -> &SmallVec<[GenericArg; 2]> {
         &self.0
     }