I’ve used Logger.metadata before (along the lines of this post), but I’m having some trouble making it work from within a Mix task.

Assuming the following in my config:

config :logger, :console,
  level: :debug,
  format: "[$level] $message [metadata] $metadata\n",
   metadata: [:foo]

and a run/1 function in a custom mix task like so:

  def run(opts) do
    {:ok, _} = Application.ensure_all_started(:my_app)
    Logger.metadata(foo: "XZ")
    Logger.info("wtf?")
  end

I would expect the log output to be something like this:

08:42:30.012 [info] wtf? [metadata] state=XZ

That’s what I get when I try this inside iex, but instead, it only outputs the message:

08:42:30.012 [info]  wtf?

Can someone explain this? Does have something to do with the metadata only applying to the current process?

Thanks, as always!