Memoize reference_pattern/link_reference_pattern

These methods are called quite often in loops so by memoizing their
output we can reduce timings a bit.

app/models/commit.rb

@@ -74,14 +74,14 @@ class Commit
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (?:#{Project.reference_pattern}#{reference_prefix})?
       (?<commit>\h{7,40})
     }x
   end
   def self.link_reference_pattern
-    super("commit", /(?<commit>\h{7,40})/)
+    @link_reference_pattern ||= super("commit", /(?<commit>\h{7,40})/)
   end
   def to_reference(from_project = nil)

app/models/commit_range.rb

@@ -43,14 +43,14 @@ class CommitRange
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (?:#{Project.reference_pattern}#{reference_prefix})?
       (?<commit_range>#{STRICT_PATTERN})
     }x
   end
   def self.link_reference_pattern
-    super("compare", /(?<commit_range>#{PATTERN})/)
+    @link_reference_pattern ||= super("compare", /(?<commit_range>#{PATTERN})/)
   end
   # Initialize a CommitRange

app/models/external_issue.rb

@@ -31,7 +31,7 @@ class ExternalIssue
   # Pattern used to extract `JIRA-123` issue references from text
   def self.reference_pattern
-    %r{(?<issue>\b([A-Z][A-Z0-9_]+-)\d+)}
+    @reference_pattern ||= %r{(?<issue>\b([A-Z][A-Z0-9_]+-)\d+)}
   end
   def to_reference(_from_project = nil)

app/models/issue.rb

@@ -73,14 +73,14 @@ class Issue < ActiveRecord::Base
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<issue>\d+)
     }x
   end
   def self.link_reference_pattern
-    super("issues", /(?<issue>\d+)/)
+    @link_reference_pattern ||= super("issues", /(?<issue>\d+)/)
   end
   def to_reference(from_project = nil)

app/models/label.rb

@@ -56,7 +56,7 @@ class Label < ActiveRecord::Base
   # This pattern supports cross-project references.
   #
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}
       (?:

app/models/merge_request.rb

@@ -149,14 +149,14 @@ class MergeRequest < ActiveRecord::Base
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<merge_request>\d+)
     }x
   end
   def self.link_reference_pattern
-    super("merge_requests", /(?<merge_request>\d+)/)
+    @link_reference_pattern ||= super("merge_requests", /(?<merge_request>\d+)/)
   end
   # Returns all the merge requests from an ActiveRecord:Relation.

app/models/milestone.rb

@@ -79,7 +79,7 @@ class Milestone < ActiveRecord::Base
   end
   def self.link_reference_pattern
-    super("milestones", /(?<milestone>\d+)/)
+    @link_reference_pattern ||= super("milestones", /(?<milestone>\d+)/)
   end
   def self.upcoming

app/models/snippet.rb

@@ -56,14 +56,14 @@ class Snippet < ActiveRecord::Base
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{
+    @reference_pattern ||= %r{
       (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<snippet>\d+)
     }x
   end
   def self.link_reference_pattern
-    super("snippets", /(?<snippet>\d+)/)
+    @link_reference_pattern ||= super("snippets", /(?<snippet>\d+)/)
   end
   def to_reference(from_project = nil)