You can try using GitHub - ast-grep/ast-grep: ⚡A CLI tool for code structural search, lint and rewriting. Written in Rust.

Given this input on my machine:

# Put this in f.ex. `test.ex`

defmodule Notifications.External do
  def schedule(user_id, link, notification_type, metadata) do
    IO.puts(
      "Scheduling stuff for user #{user_id}: " <>
        " link=#{link}, " <>
        "notification_type=#{notification_type}, " <> "metadata=#{inspect(metadata)}"
    )
  end
end

defmodule UserModuleOne do
  def function_one() do
    Notifications.External.schedule(1, "nope", :ticket_created, %{})
  end
end

defmodule UserModuleTwo do
  def function_two() do
    Notifications.External.schedule(2, "never", :ticket_updated, %{})
  end
end

defmodule UserModuleThree do
  def function_three() do
    Notifications.External.schedule(3, "not_happening", :ticket_closed, %{})

    task1 =
      Task.async(fn ->
        Notifications.External.schedule(4, "gone", :ticket_removed, %{})
      end)

    task2 =
      Task.async(fn ->
        Notifications.External.schedule(5, "you_serious?", :ticket_closed, %{})
      end)

    Task.await_many([task1, task2])
  end
end

Then you just run this:

sg -l ex -p 'Notifications.External.schedule($USER_ID, $LINK, $TYPE, $METADATA)' --rewrite '$TYPE' --json=compact | jq -r '.[] | .replacement' | sort | uniq

And that gives you:

:ticket_closed
:ticket_created
:ticket_removed
:ticket_updated

NOTE: it’s not perfect f.ex. if you have code that does alias Notifications.External and then calls External.schedule(...) then this incantation will not catch it. Though you can also make variants for any levels of nesting i.e. replace the pattern Notifications.External.schedule($USER_ID, $LINK, $TYPE, $METADATA) with External.schedule($USER_ID, $LINK, $TYPE, $METADATA) and you should be good. (And then you should be doing a union of all these results which is pretty easy with cat and then doing sort | uniq again.)