Reduce extra object creations in TaggedLogging

tags_text method creates 3 Ruby objects per each logger call when no custom tags are given
(which is the default setting, and so presumably the majority use case).
This patch reduces two temporary object creations in this case.

    require 'allocation_tracer'
    ObjectSpace::AllocationTracer.setup(%i{type})

    tags = ['a']

    pp before: ObjectSpace::AllocationTracer.trace {
      tags.collect { |tag| "[#{tag}] " }.join
    }

    pp after: ObjectSpace::AllocationTracer.trace {
      "[#{tags[0]}] "
    }

    {:before=>{[:T_ARRAY]=>[1, 0, 0, 0, 0, 0], [:T_STRING]=>[2, 0, 0, 0, 0, 0]}}
    {:after=>{[:T_STRING]=>[1, 0, 0, 0, 0, 0]}}

1 files changed, 3 insertions, 1 deletions

diff --git a/activesupport/lib/active_support/tagged_logging.rb b/activesupport/lib/active_support/tagged_logging.rb
index 8561cba9f1..b069ac94d4 100644
--- a/activesupport/lib/active_support/tagged_logging.rb
+++ b/activesupport/lib/active_support/tagged_logging.rb
@@ -52,7 +52,9 @@ module ActiveSupport
 
       def tags_text
         tags = current_tags
-        if tags.any?
+        if tags.one?
+          "[#{tags[0]}] "
+        elsif tags.any?
           tags.collect { |tag| "[#{tag}] " }.join
         end
       end