Add edit utility for adding an associated item list to a impl def

Author: M-J-Hooper

crates/syntax/src/ast/edit.rs

@@ -93,6 +93,22 @@ where
     }
 }
 
+impl ast::Impl {
+    #[must_use]
+    pub fn with_items(&self, items: ast::AssocItemList) -> ast::Impl {
+        let mut to_insert: ArrayVec<[SyntaxElement; 2]> = ArrayVec::new();
+        if let Some(old_items) = self.assoc_item_list() {
+            let to_replace: SyntaxElement = old_items.syntax().clone().into();
+            to_insert.push(items.syntax().clone().into());
+            self.replace_children(single_node(to_replace), to_insert)
+        } else {
+            to_insert.push(make::tokens::single_space().into());
+            to_insert.push(items.syntax().clone().into());
+            self.insert_children(InsertPosition::Last, to_insert)
+        }
+    }
+}
+
 impl ast::AssocItemList {
     #[must_use]
     pub fn append_items(