[erlang-questions] Debugging apps with dependencies

[Bob Ippolito]

On Mon, Apr 30, 2012 at 11:05 AM, Josh Black <raskchanky@REDACTED> wrote:

> Hi, erlang beginner here.
>
> I have a question about the best way to debug apps which include
> dependencies.
>
> I'm working on an app, and so far, I've been testing it by using rebar to
> generate a release, then starting a console for the release and going from
> there.  The problem comes when I want to use something like dbg or appmon
> to debug errors or inspect the state of my app.  When I try to do, e.g.
> appmon:start() from the console for my release, it tells me "undefined
> function appmon:start/0".  I'm guessing this is because I didn't explicitly
> specify appmon in my release configuration?
>
> Alternatively, I created a start.sh shell script with contents like this:
>
> erl -pa apps/*/ebin -pa deps/*/ebin -eval 'application:start(dependency1),
> application:start(dependency2), application:start(myapp).'
>
> This lets me start appmon and whatever else I want when I run into errors,
> but feels pretty messy and wrong.
>
> I feel like I'm missing something really obvious here.  What's the correct
> way to do this?
>

I haven't discovered a great workflow for developing with releases either,
but you can start dependencies in a slightly cleaner way by looking at the
app file:

This would go in some module with the same name as the application, and you
would call it with "erl ... -s modname"

-export([start/0]).

start() -> start(?MODULE).

start(App) ->
    application:load(App),
    {ok, Deps} = application:get_key(App, applications),
    lists:foreach(fun start_app/1, Deps),
    application:start(App).

start_app(App) ->
    case application:start(App) of
        {error, {already_started, _}} -> ok;
        ok -> ok
    end.
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