Observer in iex -S mix error: (UndefinedFunctionError) function :wx_object.start/3 is undefined

:observer is a module in the :runtime_tools application. You’d need to add the latter.

works for me

extra_applications: [:logger, :wx, :observer, :runtime_tools]

Thanks! I had :runtime_tools but missed :wx, it works!

If you don’t want to modify your application you could also run this in IEx:

Mix.ensure_application!(:wx)
Mix.ensure_application!(:runtime_tools)
Mix.ensure_application!(:observer)
:observer.start()

I can confirm that, from Erlang/OTP 27, only:

Mix.ensure_application!(:observer)
:observer.start()

is required.

This does seem to work, but it’s still necessary to include both :wx and :observer in :extra_applications. Is this intended?

I did some tests locally and that did not seem to be required, only Mix.ensure_application!(:observer); :observer.start() from Erlang/OTP 27.

Sorry, I wasn’t very clear. What I mean is that the following works:

$ mix new foo && cd foo
$ iex -S mix
iex> Mix.ensure_application!(:observer); :observer.start()

But this doesn’t:

$ mix new foo && cd foo
$ vim mix.exs # or whatever
# add :observer to :extra_applications list in application/0
$ iex -S mix
iex> :observer.start()

I thought both should work, and the docs for Mix.ensure_application!/1 sort of imply they’re typically functionally equivalent.

You need to add :wx to extra applications because it is an optional dependency of :observer. The ensure_application! also considers optional dependencies.

Hi there!

I might misunderstood what you said there, but despite running Erlang/OTP 27 and Elixir 1.17 it still seems that :observer is not enough:

iex -S mix
iex(1)> Mix.ensure_application!(:observer)
:ok
iex(2)> :observer.start()
** (UndefinedFunctionError) function :wx_object.start/3 is undefined (module :wx_object is not available)
    :wx_object.start(:observer_wx, [], [])
    (observer 2.16) observer_wx.erl:71: :observer_wx.start/0
    iex:2: (file)

From what I understand from this:

Is that Mix.ensure_application!(:observer) should be failing due to :wx not being there. Is that correct?