1 files changed, 26 insertions, 3 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 98ba05fc2..e97b81473 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -196,7 +196,12 @@ struct InferenceContext<'a, D: HirDatabase> {
     trait_env: Arc<TraitEnvironment>,
     obligations: Vec<Obligation>,
     result: InferenceResult,
-    /// The return type of the function being inferred.
+    /// The return type of the function being inferred, or the closure if we're
+    /// currently within one.
+    ///
+    /// We might consider using a nested inference context for checking
+    /// closures, but currently this is the only field that will change there,
+    /// so it doesn't make sense.
     return_ty: Ty,
 
     /// Impls of `CoerceUnsized` used in coercion.
@@ -363,14 +368,26 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     }
 
     fn resolve_associated_type(&mut self, inner_ty: Ty, assoc_ty: Option<TypeAliasId>) -> Ty {
+        self.resolve_associated_type_with_params(inner_ty, assoc_ty, &[])
+    }
+
+    fn resolve_associated_type_with_params(
+        &mut self,
+        inner_ty: Ty,
+        assoc_ty: Option<TypeAliasId>,
+        params: &[Ty],
+    ) -> Ty {
         match assoc_ty {
             Some(res_assoc_ty) => {
                 let ty = self.table.new_type_var();
+                let builder = Substs::build_for_def(self.db, res_assoc_ty)
+                    .push(inner_ty)
+                    .fill(params.iter().cloned());
                 let projection = ProjectionPredicate {
                     ty: ty.clone(),
                     projection_ty: ProjectionTy {
                         associated_ty: res_assoc_ty,
-                        parameters: Substs::single(inner_ty),
+                        parameters: builder.build(),
                     },
                 };
                 self.obligations.push(Obligation::Projection(projection));
@@ -443,7 +460,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     }
 
     fn infer_body(&mut self) {
-        self.infer_expr(self.body.body_expr, &Expectation::has_type(self.return_ty.clone()));
+        self.infer_expr_coerce(self.body.body_expr, &Expectation::has_type(self.return_ty.clone()));
     }
 
     fn resolve_into_iter_item(&self) -> Option<TypeAliasId> {
@@ -517,6 +534,12 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         let struct_ = self.resolver.resolve_known_struct(self.db, &path)?;
         Some(struct_.into())
     }
+
+    fn resolve_ops_index_output(&self) -> Option<TypeAliasId> {
+        let path = path![std::ops::Index];
+        let trait_ = self.resolver.resolve_known_trait(self.db, &path)?;
+        self.db.trait_data(trait_).associated_type_by_name(&name![Output])
+    }
 }
 
 /// The kinds of placeholders we need during type inference. There's separate