Catch error case when prewalk fails to replace ast

lib/next_ls/commands/to_pipe.ex

@@ -40,7 +40,8 @@ defmodule NextLS.Commands.ToPipe do
   defp to_pipe_edit(text, position) do
     with {:ok, ast} <- code_to_ast(text),
          {:ok, first_argument_ast} <- get_function_or_argument_to_pipe(ast, position),
-         {edit, range} = get_edit(ast, first_argument_ast),
+         {:ok, new_ast} <- extract_to_pipe(ast, first_argument_ast),
+         {edit, range} = get_edit(new_ast),
          {:ok, indent} = EditHelpers.get_indent(text, range.start.line),
          edit <- EditHelpers.add_indent_to_edit(edit, indent) do
       {:ok, %TextEdit{new_text: edit, range: range}}
@@ -56,11 +57,9 @@ defmodule NextLS.Commands.ToPipe do
     |> Spitfire.parse()
   end
 
-  defp get_edit(ast, first_argument) do
-    new_ast = extract_to_pipe(ast, first_argument)
+  defp get_edit(new_ast) do
     {pipe, open, args = [_arg1, {_, context, _}]} = new_ast
-    ast = {pipe, [], args}
-    edit = Macro.to_string(ast)
+    edit = Macro.to_string({pipe, [], args})
 
     open = if open[:line], do: open, else: context
     closing = context[:closing] || context[:end_of_expression] || context[:end]
@@ -75,7 +74,7 @@ defmodule NextLS.Commands.ToPipe do
 
   @conditionals [:if, :case, :unless]
   defp extract_to_pipe(ast, {call, context, _args} = arg_ast) do
-    {_changed_ast, {new_ast, true}} =
+    {_changed_ast, {new_ast, changed}} =
       Macro.prewalk(ast, {_new_ast = nil, _changed = false}, fn
         {^call, ^context, [first | rest]}, {_, false} ->
           new_ast = {:|>, context, [first, {call, context, rest}]}
@@ -102,7 +101,11 @@ defmodule NextLS.Commands.ToPipe do
           {ast, acc}
       end)
 
-    new_ast
+    if changed do
+      {:ok, new_ast}
+    else
+      {:error, "could not change the ast"}
+    end
   end
 
   @elixir_macros [:def, :defmodule, :__aliases__]