Should `__info__(:attributes)` accumulate multiple instances of the same attribute?

There’s already a setting for module attributes, which controls if their values are accumulated or replaced.

Even more concretely: Module.register_attribute

defmodule Xyz do
  Module.register_attribute(__MODULE__, :cars, accumulate: true)

  @cars "Toyota"

  def do_stuff(), do: IO.puts("hey there")

  @cars ", "
  @cars "Hyundai"

  def show_cars(), do: IO.puts(@cars)
end

Then in iex:

iex(1)> Xyz.show_cars()
Hyundai, Toyota
:ok

Note that if you put integers they’ll be accumulated in a list. Strings however just get appended at the end of the previous value.

actually it doesn’t fix it… sure it works for when you use the attribute again as in your example but in the __info__(:attributes) will still have 2 entries instead of just one:
for example:

defmodule Abc do
  Module.register_attribute(__MODULE__, :behaviour, accumulate: true)
  use GenServer
  @behaviour MyBehaviour
...
end

Then in iex __info__(:attributes) will be:

iex(1)> Abc.__info__(:attributes)
[vsn: [...],
behaviour: [GenServer],
behaviour: [MyBehaviour]]

I see. You can still use Keyword.get_values though.

Looks weird, I agree.
Could you elaborate more on the use case? How do you approach this check?

That’s how Erlang stores multiple attributes, which we reproduce for compatibility.

It was for this PR
https://github.com/dashbitco/broadway_rabbitmq/pull/126

I assumed it would accumulate, and did a wrong implementation in the first PR:
https://github.com/dashbitco/broadway_rabbitmq/pull/118