Fix config.log_level being ignored when using a Broadcast Logger:

- ### Problem

  If an application has configured a Broadcast Logger, setting the
  `config.log_level` to any value has no effect:

  ```ruby
  # config/application.rb

  config.logger = ActiveSupport::BroadcastLogger.new(Logger.new(STDOUT))
  config.log_level = :warn

  puts Rails.logger.broadcasts.map(&:level) # => [Logger::DEBUG]
  ```

  This is a side effect of #49621 which tried to fix the `log_level`
  default value overriding the whole broadcasts.

  ### Context

  The `log_level` default's value shouldn't apply to a Broadcast
  Logger, as otherwise it overrides whatever the application
  previously configured. While this behaviour is the same with
  a vanilla logger, at least we can workaround it:

  ```ruby
  # When using a vanilla logger

  config.logger = Logger.new(STDOUT, level: LOGGER::WARN)
  # Once the app boots, the level is overriden to DEBUG. We need to add the following line.
  config.log_level = :warn

  # When using a broadcast logger

  stdout = Logger.new(STDOUT, level: Logger::INFO)
  stderr = Logger.new(STDERR, level: Logger::ERROR)
  config.logger = ActiveSupport::BroadcastLogger(stdout, stderr)

  # Once the app boots the whole broadcast level is overriden to DEBUG.
  # There is no way to workaround this as you can't fine grain the level of each
  # loggers with `config.log_level=`.
  ```

  ### Solution

  This PR ignores the default `log_level` value when using a Broadcast Logger,
  but ensure it gets used if an application manually sets it.

  Fix #50324

railties/lib/rails/application/bootstrap.rb

@@ -55,7 +55,11 @@ module Bootstrap
           logger
         end
 
-        unless Rails.logger.is_a?(ActiveSupport::BroadcastLogger)
+        if Rails.logger.is_a?(ActiveSupport::BroadcastLogger)
+          if config.broadcast_log_level
+            Rails.logger.level = ActiveSupport::Logger.const_get(config.broadcast_log_level.to_s.upcase)
+          end
+        else
           Rails.logger.level = ActiveSupport::Logger.const_get(config.log_level.to_s.upcase)
           broadcast_logger = ActiveSupport::BroadcastLogger.new(Rails.logger)
           broadcast_logger.formatter = Rails.logger.formatter

railties/lib/rails/application/configuration.rb

@@ -19,13 +19,13 @@ class Configuration < ::Rails::Engine::Configuration
                     :ssl_options, :public_file_server,
                     :session_options, :time_zone, :reload_classes_only_on_change,
                     :beginning_of_week, :filter_redirect, :x,
-                    :read_encrypted_secrets, :log_level, :content_security_policy_report_only,
+                    :read_encrypted_secrets, :content_security_policy_report_only,
                     :content_security_policy_nonce_generator, :content_security_policy_nonce_directives,
                     :require_master_key, :credentials, :disable_sandbox, :sandbox_by_default,
                     :add_autoload_paths_to_load_path, :rake_eager_load, :server_timing, :log_file_size,
                     :dom_testing_default_html_version
 
-      attr_reader :encoding, :api_only, :loaded_config_version
+      attr_reader :encoding, :api_only, :loaded_config_version, :log_level
 
       def initialize(*)
         super
@@ -373,6 +373,15 @@ def api_only=(value)
         @debug_exception_response_format ||= :api
       end
 
+      def log_level=(level)
+        @log_level = level
+        @broadcast_log_level = level
+      end
+
+      def broadcast_log_level # :nodoc:
+        defined?(@broadcast_log_level) ? @broadcast_log_level : nil
+      end
+
       def debug_exception_response_format
         @debug_exception_response_format || :default
       end

railties/test/application/configuration_test.rb

@@ -1949,6 +1949,31 @@ def index
       assert_equal Logger::DEBUG, Rails.logger.level
     end
 
+    test "config.log_level does not override the level of the broadcast with the default value" do
+      add_to_config <<-RUBY
+        stdout = Logger.new(STDOUT, level: Logger::INFO)
+        stderr = Logger.new(STDERR, level: Logger::ERROR)
+        config.logger = ActiveSupport::BroadcastLogger.new(stdout, stderr)
+      RUBY
+
+      app "development"
+
+      assert_equal([Logger::INFO, Logger::ERROR], Rails.logger.broadcasts.map(&:level))
+    end
+
+    test "config.log_level overrides the level of the broadcast when a custom value is set" do
+      add_to_config <<-RUBY
+        stdout = Logger.new(STDOUT)
+        stderr = Logger.new(STDERR)
+        config.logger = ActiveSupport::BroadcastLogger.new(stdout, stderr)
+        config.log_level = :warn
+      RUBY
+
+      app "development"
+
+      assert_equal([Logger::WARN, Logger::WARN], Rails.logger.broadcasts.map(&:level))
+    end
+
     test "config.logger when logger is already a Broadcast Logger" do
       logger = ActiveSupport::BroadcastLogger.new