Fix TaggedLogging to allow loggers to be instantiated multiple times without...

Fix TaggedLogging to allow loggers to be instantiated multiple times without having to share the stack of tags. This is accomplished by using a unique key for the thread-local tag list. Fixes #9064.

activesupport/lib/active_support/tagged_logging.rb

@@ -42,7 +42,9 @@ def clear_tags!
       end
 
       def current_tags
-        Thread.current[:activesupport_tagged_logging_tags] ||= []
+        # We use our object ID here to void conflicting with other instances
+        thread_key = @thread_key ||= "activesupport_tagged_logging_tags:#{object_id}".freeze
+        Thread.current[thread_key] ||= []
       end
 
       private

activesupport/test/tagged_logging_test.rb

@@ -79,6 +79,19 @@ def flush(*)
     assert_equal "[OMG] Cool story bro\n[BCX] Funky time\n", @output.string
   end
 
+  test "keeps each tag in their own instance" do
+    @other_output = StringIO.new
+    @other_logger = ActiveSupport::TaggedLogging.new(MyLogger.new(@other_output))
+    @logger.tagged("OMG") do
+      @other_logger.tagged("BCX") do
+        @logger.info "Cool story bro"
+        @other_logger.info "Funky time"
+      end
+    end
+    assert_equal "[OMG] Cool story bro\n", @output.string
+    assert_equal "[BCX] Funky time\n", @other_output.string
+  end
+
   test "cleans up the taggings on flush" do
     @logger.tagged("BCX") do
       Thread.new do