`iex` crashes with recent erlang installs

I cannot reproduce it locally. Do you have a custom prompt or any IEx configuration?

Sometimes I feel very dumb. Turns out I do have a custom .iex.exs, I just didn’t recall creating it.

IEx.configure(
  colors: [
    enabled: true
  ],
  default_prompt: [
      "\e[G",     # ANSI CHA, move cursor to column 1
      "\e[35m",   # ANSI magenta
      "%prefix",  # IEx prompt variable
      ">",        # plain string
      "\e[0m"     # ANSI reset
    ] |> IO.chardata_to_string
)

I have no idea where that comes from. Removing it resolves the issue (of course).

Thank you

This is definitely a bug though, we would need to isolate and report it upstream. My guess is that Erlang doesn’t like ANSI in prompts.

I have a similar customized terminal prompt and recently hit this same error (on ubuntu 20.04) after upgrading to OTP-26.

After eliminating the first line that moves the cursor to column 1 and converting the other values to atoms resolved the error for me:

  IEx.configure(
    colors: [
      syntax_colors: [
        number: :light_yellow,
        atom: :light_cyan,
        string: :light_black,
        boolean: [:light_blue],
        nil: [:magenta, :bright]
      ],
      ls_directory: :cyan,
      ls_device: :yellow,
      doc_code: :green,
      doc_inline_code: :magenta,
      doc_headings: [:cyan, :underline],
      doc_title: [:cyan, :bright, :underline]
    ],
    default_prompt:
      [
        :light_magenta,
        "🧪 iex",
        ">",
        :white,
        :reset
      ]
      |> IO.ANSI.format()
      |> IO.chardata_to_string()
  )

I tried this, but without the “move cursor to column 1” when you hit up or down arrows to scroll through history, it seems to continuously build the prompt. (ie: keeps adding additional to start of prompt)

Yes. I previously had that line in my .iex.exs file but it broke functionality after upgrading to OTP 26. By this I mean that hitting up and trying to rerun previous commands failed.

Removing the line, IEX is usable, but the UI issue with duplicating s in the prompt happens. I’m not sure why the "\e[G" (move cursor to column 1) line broke on OTP 26, and still need to look into it further.

I just tested the quoted code above with Elixir 1.17 and OTP 27 and the ANSI CHA line still causes crashes.

However the issue of duplicating s when the line is removed. I.e., the config you quoted above behaves normally when scrolling through IEX history on current language versions.

As of Elixir 1.17.2-otp-27, this problem resolved for me and I reverted the default_prompt section of my IEx.configure back to the following:

    default_prompt:
      [
        "\e[G",
        :light_magenta,
        "🧪 iex",
        "(%counter)>",
        :white,
        :reset
      ]
      |> IO.ANSI.format()
      |> IO.chardata_to_string()