In case anyone stumbles across this question in their own question, the following is suitable for me needs:
defmacro warn_once(key, message, level \\ :warn) do
caller = __CALLER__.module
quote do
require Logger
if :persistent_term.get({unquote(caller), unquote(key)}, true) do
Logger.unquote(level)(unquote(message))
:persistent_term.put({unquote(caller), unquote(key)}, nil)
end
end
end
I wrap this at the calling site with a macro to make the inclusion of this generated code dependent on configuration, and whether :persistent_term exists.
