Surround Project.reference_pattern in parenthesis inside other patterns

app/models/commit.rb

@@ -72,7 +72,10 @@ class Commit
   #
   # This pattern supports cross-project references.
   def self.reference_pattern
-    %r{(?:#{Project.reference_pattern}#{reference_prefix})?(?<commit>\h{6,40})}
+    %r{
+      (?:#{Project.reference_pattern}#{reference_prefix})?
+      (?<commit>\h{6,40})
+    }x
   end
   def to_reference(from_project = nil)

app/models/issue.rb

@@ -63,7 +63,7 @@ class Issue < ActiveRecord::Base
   # This pattern supports cross-project references.
   def self.reference_pattern
     %r{
-      #{Project.reference_pattern}?
+      (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<issue>\d+)
     }x
   end

app/models/merge_request.rb

@@ -145,7 +145,7 @@ class MergeRequest < ActiveRecord::Base
   # This pattern supports cross-project references.
   def self.reference_pattern
     %r{
-      #{Project.reference_pattern}?
+      (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<merge_request>\d+)
     }x
   end

app/models/snippet.rb

@@ -61,7 +61,7 @@ class Snippet < ActiveRecord::Base
   # This pattern supports cross-project references.
   def self.reference_pattern
     %r{
-      #{Project.reference_pattern}?
+      (#{Project.reference_pattern})?
       #{Regexp.escape(reference_prefix)}(?<snippet>\d+)
     }x
   end