Exbug

A more traditional experience for the :debugger module

Installation

by adding exbug to your list of dependencies in mix.exs:

def deps do
  [{:exbug, "~> 0.1.0", only: :dev}]
end

Documentation found at https://hexdocs.pm/exbug.

Explanation

Provides a traditional debugging experince for Elixir by providing a thin layer around the :debugger & :int modules. To be used with iex -S mix.

How it works

Be warned, this is more of a hack than anything. I feel pretty dirty about it, but here we go.

Background

the iex shell is a great tool. It’s so great, it can event be customised with a .iex.exs file. IEx will load this file if it’s present in the directory in which iex is run.

iex.exs hack

Exbug.__using__/1 appends your .iex.exs file with the code needed to

• Start the Erlang graphical debugger
• Mark the hosting module for debugging

debug/0

Next, to set a breakpoint you must use the debug/0 function. It marks sets a breakpoint on the same line the debug() statement is on. I’m sorry for the next part.

Next, it uses :timer.sleep/1 to sleep the calling process until the :debugger and :int module have time to catch up to the calling process.

Why would you do that?!

As you would suspect, the :debugger & :int modules runs in a different process to the calling module. If you don’t sleep the calling process, the code will continue executing and the breakpoint won’t be set in time.

Please don’t use this in production.

What about my existing .iex.exs file?

Exbug uses deliminters to denote any appended code. The @on_load attribute is used so that when the Exbug module is loaded, and previously appended Exbug code is cleaned out and removed

Examples

  # controller.ex
  defmodule Controller do
    use Exbug

    def show(conn, _) do
        debug()
        # ...
    end
  end

  > mix compile --force && iex -S mix
  ...
  iex> Controller.show(conn, nil)
  # debugger is started and breakpoint is hit