Logger filter doesn't document successful return state properly

[dssecret]

Elixir and Erlang/OTP versions

Erlang/OTP 28 [erts-16.0.1] [source] [64-bit] [smp:20:20] [ds:20:20:10] [async-threads:1] [jit:ns]

Elixir 1.18.4 (compiled with Erlang/OTP 27)

Operating system

Linux

Current behavior

The logger filter docs indicates :log to be the return value for the filter passing. But when using the :log return value, the filter was removed (:removed_failing_filter) with the reason {:bad_return_value, :log}]. For example:

defmodule LogFilter do
  def filter(log_event, _opts) do
    case log_event do
      %{msg: {:string, msg}} when is_binary(msg) ->
        if msg =~ "password" do
          :log
        else
          :stop
        end

      _ ->
        :stop
    end
  end
end

config :repro, :logger, [
  {
    :handler,
    :repo_logger,
    :logger_std_h,
    %{
      config: %{
        file: ~c"repro.log"
      },
      formatter: Logger.Formatter.new(),
      filters: [
        repro_filter: {&LogFilter.filter/2, []}
      ],
      filter_default: :stop
    }
  }
]

Expected behavior

The erlang :logger docs indicates that the log event (log_event for the example in the Elixir docs) should be returned instead of :log. Replacing :log with %{log_event | msg: {:string, "[Filtered]"}} doesn't cause an error and continues to log properly. Also, based on erlang's logging guide, shouldn't :ignore be used when the filter passes unless the log event is being changed by the filter which isn't really what Elixir's docs say?

[josevalim]

You are correct on all accounts. Would you like to send a PR updating the docs?