2 files changed, 16 insertions, 8 deletions

diff --git a/crates/ra_assists/src/assists/add_missing_impl_members.rs b/crates/ra_assists/src/assists/add_missing_impl_members.rs
index 22f1157cc..942b34dc1 100644
--- a/crates/ra_assists/src/assists/add_missing_impl_members.rs
+++ b/crates/ra_assists/src/assists/add_missing_impl_members.rs
@@ -207,25 +207,23 @@ fn get_syntactic_substs(impl_block: ast::ImplBlock) -> Option<Vec<ast::TypeRef>>
 }
 
 // FIXME: This should be a general utility (not even just for assists)
-fn substitute_type_params<N: AstNode>(
+fn substitute_type_params<N: AstNode + Clone>(
     db: &impl HirDatabase,
     node: hir::InFile<N>,
     substs: &HashMap<hir::TypeParam, ast::TypeRef>,
 ) -> N {
     let type_param_replacements = node
-        .value
-        .syntax()
-        .descendants()
-        .filter_map(ast::TypeRef::cast)
+        .clone()
+        .descendants::<ast::TypeRef>()
         .filter_map(|n| {
-            let path = match &n {
+            let path = match &n.value {
                 ast::TypeRef::PathType(path_type) => path_type.path()?,
                 _ => return None,
             };
-            let analyzer = hir::SourceAnalyzer::new(db, node.with_value(n.syntax()), None);
+            let analyzer = hir::SourceAnalyzer::new(db, n.syntax(), None);
             let resolution = analyzer.resolve_path(db, &path)?;
             match resolution {
-                hir::PathResolution::TypeParam(tp) => Some((n, substs.get(&tp)?.clone())),
+                hir::PathResolution::TypeParam(tp) => Some((n.value, substs.get(&tp)?.clone())),
                 _ => None,
             }
         })
diff --git a/crates/ra_hir_expand/src/lib.rs b/crates/ra_hir_expand/src/lib.rs
index 2fa5d5140..51c5f9623 100644
--- a/crates/ra_hir_expand/src/lib.rs
+++ b/crates/ra_hir_expand/src/lib.rs
@@ -322,3 +322,13 @@ impl InFile<SyntaxNode> {
         })
     }
 }
+
+impl<N: AstNode> InFile<N> {
+    pub fn descendants<T: AstNode>(self) -> impl Iterator<Item = InFile<T>> {
+        self.value.syntax().descendants().filter_map(T::cast).map(move |n| self.with_value(n))
+    }
+
+    pub fn syntax(&self) -> InFile<&SyntaxNode> {
+        self.with_value(self.value.syntax())
+    }
+}