add AttrsOwnerEdit::add_attr

crates/syntax/src/ast/edit_in_place.rs

@@ -213,6 +213,28 @@ pub trait AttrsOwnerEdit: ast::HasAttrs {
             }
         }
     }
+
+    fn add_attr(&self, attr: ast::Attr) {
+        add_attr(self.syntax(), attr);
+
+        fn add_attr(node: &SyntaxNode, attr: ast::Attr) {
+            let indent = IndentLevel::from_node(node);
+            attr.reindent_to(indent);
+
+            let after_attrs_and_comments = node
+                .children_with_tokens()
+                .find(|it| !matches!(it.kind(), WHITESPACE | COMMENT | ATTR))
+                .map_or(Position::first_child_of(node), |it| Position::before(it));
+
+            ted::insert_all(
+                after_attrs_and_comments,
+                vec![
+                    attr.syntax().clone().into(),
+                    make::tokens::whitespace(&format!("\n{indent}")).into(),
+                ],
+            )
+        }
+    }
 }
 
 impl<T: ast::HasAttrs> AttrsOwnerEdit for T {}