PERF: dedupe scanned route fragments

Per: https://bugs.ruby-lang.org/issues/13077 String @- will dedupe strings. 

This takes advantage of this by deduping route fragments that are full of duplication usually. 

For Discourse:

Before:

Total allocated: 207574305 bytes (2214916 objects)
Total retained:  36470010 bytes (322194 objects)

After 

Total allocated: 207556847 bytes (2214711 objects)
Total retained:  36327973 bytes (318627 objects) <- object that GC can not collect


So we save 3500 or so RVALUES this way, not the largest saving in the world, but worth it especially for large route files.

1 files changed, 11 insertions, 4 deletions

diff --git a/actionpack/lib/action_dispatch/journey/scanner.rb b/actionpack/lib/action_dispatch/journey/scanner.rb
index 4ae77903fa..5ed587c1b1 100644
--- a/actionpack/lib/action_dispatch/journey/scanner.rb
+++ b/actionpack/lib/action_dispatch/journey/scanner.rb
@@ -33,6 +33,13 @@ module ActionDispatch
       end
 
       private
+      
+        # takes advantage of String @- deduping capabilities in Ruby 2.5 upwards
+        # see: https://bugs.ruby-lang.org/issues/13077
+        def dedup_scan(regex)
+          r = @ss.scan(regex)
+          r ? -r : nil
+        end
 
         def scan
           case
@@ -47,15 +54,15 @@ module ActionDispatch
             [:OR, "|"]
           when @ss.skip(/\./)
             [:DOT, "."]
-          when text = @ss.scan(/:\w+/)
+          when text = dedup_scan(/:\w+/)
             [:SYMBOL, text]
-          when text = @ss.scan(/\*\w+/)
+          when text = dedup_scan(/\*\w+/)
             [:STAR, text]
-          when text = @ss.scan(/(?:[\w%\-~!$&'*+,;=@]|\\[:()])+/)
+          when text = dedup_scan(/(?:[\w%\-~!$&'*+,;=@]|\\[:()])+/)
             text.tr! "\\", ""
             [:LITERAL, text]
             # any char
-          when text = @ss.scan(/./)
+          when text = dedup_scan(/./)
             [:LITERAL, text]
           end
         end