Merge branch 'perf-wiki-pattern-once' into 'master'

Improve render performance of large wiki pages

See merge request gitlab-org/gitlab-ce!20465

changelogs/unreleased/perf-wiki-pattern-once.yml

+---
+title: Improve render performance of large wiki pages
+merge_request: 20465
+author: Peter Leitzen
+type: performance

lib/banzai/filter/abstract_reference_filter.rb

@@ -100,6 +100,11 @@ module Banzai
         ref_pattern = object_class.reference_pattern
         link_pattern = object_class.link_reference_pattern
 
+        # Compile often used regexps only once outside of the loop
+        ref_pattern_anchor = /\A#{ref_pattern}\z/
+        link_pattern_start = /\A#{link_pattern}/
+        link_pattern_anchor = /\A#{link_pattern}\z/
+
         nodes.each do |node|
           if text_node?(node) && ref_pattern
             replace_text_when_pattern_matches(node, ref_pattern) do |content|
@@ -108,7 +113,7 @@ module Banzai
 
           elsif element_node?(node)
             yield_valid_link(node) do |link, inner_html|
-              if ref_pattern && link =~ /\A#{ref_pattern}\z/
+              if ref_pattern && link =~ ref_pattern_anchor
                 replace_link_node_with_href(node, link) do
                   object_link_filter(link, ref_pattern, link_content: inner_html)
                 end
@@ -118,7 +123,7 @@ module Banzai
 
               next unless link_pattern
 
-              if link == inner_html && inner_html =~ /\A#{link_pattern}/
+              if link == inner_html && inner_html =~ link_pattern_start
                 replace_link_node_with_text(node, link) do
                   object_link_filter(inner_html, link_pattern, link_reference: true)
                 end
@@ -126,7 +131,7 @@ module Banzai
                 next
               end
 
-              if link =~ /\A#{link_pattern}\z/
+              if link =~ link_pattern_anchor
                 replace_link_node_with_href(node, link) do
                   object_link_filter(link, link_pattern, link_content: inner_html, link_reference: true)
                 end