How to do CLI Tab Completion?

AndyL · January 19, 2022, 11:56pm

I want to write a CLI that does tab completion. For a comparable I studied IEx.Server.

elixir-lang/elixir/blob/main/lib/iex/lib/iex/server.ex#L132-L145

    
      
          defp loop(state, prompt, evaluator, evaluator_ref) do
            self_pid = self()
            counter = state.counter
          
          
  {prompt_type, prefix} =
              if prompt == :incomplete do
                {:continuation_prompt, "..."}
              else
                {:prompt, state.prefix}
              end
          
          
  input = spawn(fn -> io_get(self_pid, prompt_type, prefix, counter) end)
            wait_input(state, evaluator, evaluator_ref, input)
          end

It looks to me like this code takes input using IO.gets (on line 336). How does it trigger on the tab character? I can’t figure it out!

I think IO.gets traps the tab character when running under iex but not when running in elixir. Could that be right? Here’s a script test.exs that I used for testing:

#!/usr/bin/env elixir

IO.puts """
Try running this test two ways:
  > elixir text.exs
  > iex test.exs

`IO.gets` handles tab characters differently under elixir vs iex.  WHY??
"""

IO.gets("input prompt > ") |> IO.inspect(label: "RESULT")

How to write a CLI that has tab completion? Any tips appreciated!!