Allow wrapping a logger that hasn't set a formatter. Default to our SimpleFormatter. Otherwise we try extending nil with the tagging API.

activesupport/lib/active_support/tagged_logging.rb

@@ -21,10 +21,10 @@ module ActiveSupport
       end
 
       def tagged(*tags)
-        new_tags = push_tags *tags
+        new_tags = push_tags(*tags)
         yield self
       ensure
-        pop_tags new_tags.size
+        pop_tags(new_tags.size)
       end
 
       def push_tags(*tags)
@@ -55,6 +55,8 @@ module ActiveSupport
     end
 
     def self.new(logger)
+      # Ensure we set a default formatter so we aren't extending nil!
+      logger.formatter ||= ActiveSupport::Logger::SimpleFormatter.new
       logger.formatter.extend Formatter
       logger.extend(self)
     end

activesupport/test/tagged_logging_test.rb

@@ -14,6 +14,14 @@ class TaggedLoggingTest < ActiveSupport::TestCase
     @logger = ActiveSupport::TaggedLogging.new(MyLogger.new(@output))
   end
 
+  test 'sets logger.formatter if missing and extends it with a tagging API' do
+    logger = Logger.new(StringIO.new)
+    assert_nil logger.formatter
+    ActiveSupport::TaggedLogging.new(logger)
+    assert_not_nil logger.formatter
+    assert logger.formatter.respond_to?(:tagged)
+  end
+
   test "tagged once" do
     @logger.tagged("BCX") { @logger.info "Funky time" }
     assert_equal "[BCX] Funky time\n", @output.string