Fix TaggedLogging functionality when broadcasting to another logger:

activesupport/lib/active_support/logger.rb

@@ -22,6 +22,10 @@ def self.logger_outputs_to?(logger, *sources)
     # Broadcasts logs to multiple loggers.
     def self.broadcast(logger) # :nodoc:
       Module.new do
+        define_singleton_method(:extended) do |base|
+          base.public_send(:broadcast_to, logger) if base.respond_to?(:broadcast_to)
+        end
+
         define_method(:add) do |*args, &block|
           logger.add(*args, &block)
           super(*args, &block)
@@ -42,11 +46,6 @@ def self.broadcast(logger) # :nodoc:
           super(name)
         end
 
-        define_method(:formatter=) do |formatter|
-          logger.formatter = formatter
-          super(formatter)
-        end
-
         define_method(:level=) do |level|
           logger.level = level
           super(level)

activesupport/lib/active_support/tagged_logging.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "active_support/core_ext/module/delegation"
+require "active_support/core_ext/module/redefine_method"
 require "active_support/core_ext/object/blank"
 require "logger"
 require "active_support/logger"
@@ -94,6 +95,20 @@ def self.new(logger)
 
     delegate :push_tags, :pop_tags, :clear_tags!, to: :formatter
 
+    def broadcast_to(other_logger) # :nodoc:
+      define_singleton_method(:formatter=) do |formatter|
+        other_logger.formatter ||= formatter
+
+        other_logger.formatter.singleton_class.redefine_method(:current_tags) do
+          formatter.current_tags
+        end
+
+        super(formatter)
+      end
+
+      self.formatter = self.formatter.clone
+    end
+
     def tagged(*tags)
       if block_given?
         formatter.tagged(*tags) { yield self }

activesupport/test/broadcast_logger_test.rb

@@ -55,14 +55,6 @@ class BroadcastLoggerTest < TestCase
       assert_equal ::Logger::FATAL, log2.progname
     end
 
-    test "#formatter= assigns to all the loggers" do
-      assert_nil logger.formatter
-      logger.formatter = ::Logger::FATAL
-
-      assert_equal ::Logger::FATAL, log1.formatter
-      assert_equal ::Logger::FATAL, log2.formatter
-    end
-
     test "#local_level= assigns the local_level to all loggers" do
       assert_equal ::Logger::DEBUG, logger.local_level
       logger.local_level = ::Logger::FATAL

activesupport/test/tagged_logging_test.rb

@@ -226,4 +226,62 @@ class TaggedLoggingWithoutBlockTest < ActiveSupport::TestCase
     assert_equal "[OMG] Broadcasting...\n", @output.string
     assert_equal "[OMG] Broadcasting...\n", broadcast_output.string
   end
+
+  test "keeps broadcasting functionality when passed a block" do
+    broadcast_output = StringIO.new
+    broadcast_logger = ActiveSupport::TaggedLogging.new(Logger.new(broadcast_output))
+    @logger.extend(ActiveSupport::Logger.broadcast(broadcast_logger))
+
+    @logger.tagged("OMG") { |logger| logger.info "Broadcasting..." }
+
+    assert_equal "[OMG] Broadcasting...\n", @output.string
+    assert_equal "[OMG] Broadcasting...\n", broadcast_output.string
+  end
+
+  test "broadcasting when passing a block works and  keeps formatter untouched" do
+    broadcast_output = StringIO.new
+    broadcast_logger = ActiveSupport::TaggedLogging.new(Logger.new(broadcast_output))
+    my_formatter = Class.new do
+      def call(_, _, _, msg)
+        ActiveSupport::JSON.encode(message: msg, tags: current_tags)
+      end
+    end
+    broadcast_logger.formatter = my_formatter.new
+
+    @logger.extend(ActiveSupport::Logger.broadcast(broadcast_logger))
+    @logger.tagged("OMG") { |logger| logger.info "Broadcasting..." }
+
+    assert_equal "[OMG] Broadcasting...\n", @output.string
+    assert_equal "{\"message\":\"Broadcasting...\",\"tags\":[\"OMG\"]}", broadcast_output.string
+  end
+
+  test "broadcasting without passing a block works and keeps formatter untouched" do
+    broadcast_output = StringIO.new
+    broadcast_logger = ActiveSupport::TaggedLogging.new(Logger.new(broadcast_output))
+    my_formatter = Class.new do
+      def call(_, _, _, msg)
+        ActiveSupport::JSON.encode(message: msg, tags: current_tags)
+      end
+    end
+    broadcast_logger.formatter = my_formatter.new
+
+    @logger.extend(ActiveSupport::Logger.broadcast(broadcast_logger))
+    tagger_logger1 = @logger.tagged("OMG")
+    tagger_logger2 = tagger_logger1.tagged("FOO")
+    tagger_logger2.info("Broadcasting...")
+
+    assert_equal "[OMG] [FOO] Broadcasting...\n", @output.string
+    assert_equal "{\"message\":\"Broadcasting...\",\"tags\":[\"OMG\",\"FOO\"]}", broadcast_output.string
+  end
+
+  test "broadcasting on a non tagged logger" do
+    broadcast_output = StringIO.new
+    broadcast_logger = ActiveSupport::Logger.new(broadcast_output)
+
+    @logger.extend(ActiveSupport::Logger.broadcast(broadcast_logger))
+    @logger.tagged("OMG") { |logger| logger.info "Broadcasting..." }
+
+    assert_equal "[OMG] Broadcasting...\n", @output.string
+    assert_equal "Broadcasting...\n", broadcast_output.string
+  end
 end