Link issues from comments and automatically close them

Any mention of Issues, MergeRequests, or Commits via GitLab-flavored markdown
references in descriptions, titles, or attached Notes creates a back-reference
Note that links to the original referencer. Furthermore, pushing commits with
commit messages that match a (configurable) regexp to a project's default
branch will close any issues mentioned by GFM in the matched closing phrase.
If accepting a merge request would close any Issues in this way, a banner is
appended to the merge request's main panel to indicate this.

5 files changed, 29 insertions, 5 deletions

diff --git a/app/observers/activity_observer.rb b/app/observers/activity_observer.rb
index 477ebd78aeb..d754ac8185a 100644
--- a/app/observers/activity_observer.rb
+++ b/app/observers/activity_observer.rb
@@ -5,8 +5,8 @@ class ActivityObserver < BaseObserver
     event_author_id = record.author_id
 
     if record.kind_of?(Note)
-      # Skip system status notes like 'status changed to close'
-      return true if record.note.include?("_Status changed to ")
+      # Skip system notes, like status changes and cross-references.
+      return true if record.system?
 
       # Skip wall notes to prevent spamming of dashboard
       return true if record.noteable_type.blank?
diff --git a/app/observers/base_observer.rb b/app/observers/base_observer.rb
index 92b73981d27..f9a0242ce77 100644
--- a/app/observers/base_observer.rb
+++ b/app/observers/base_observer.rb
@@ -10,4 +10,8 @@ class BaseObserver < ActiveRecord::Observer
   def current_user
     Thread.current[:current_user]
   end
+
+  def current_commit
+    Thread.current[:current_commit]
+  end
 end
diff --git a/app/observers/issue_observer.rb b/app/observers/issue_observer.rb
index 50538419776..886d8b776fb 100644
--- a/app/observers/issue_observer.rb
+++ b/app/observers/issue_observer.rb
@@ -1,6 +1,8 @@
 class IssueObserver < BaseObserver
   def after_create(issue)
     notification.new_issue(issue, current_user)
+
+    issue.create_cross_references!(issue.project, current_user)
   end
 
   def after_close(issue, transition)
@@ -17,12 +19,14 @@ class IssueObserver < BaseObserver
     if issue.is_being_reassigned?
       notification.reassigned_issue(issue, current_user)
     end
+
+    issue.notice_added_references(issue.project, current_user)
   end
 
   protected
 
   # Create issue note with service comment like 'Status changed to closed'
   def create_note(issue)
-    Note.create_status_change_note(issue, issue.project, current_user, issue.state)
+    Note.create_status_change_note(issue, issue.project, current_user, issue.state, current_commit)
   end
 end
diff --git a/app/observers/merge_request_observer.rb b/app/observers/merge_request_observer.rb
index 689a25ff4b7..d70da514cd2 100644
--- a/app/observers/merge_request_observer.rb
+++ b/app/observers/merge_request_observer.rb
@@ -7,11 +7,13 @@ class MergeRequestObserver < ActivityObserver
     end
 
     notification.new_merge_request(merge_request, current_user)
+
+    merge_request.create_cross_references!(merge_request.project, current_user)
   end
 
   def after_close(merge_request, transition)
     create_event(merge_request, Event::CLOSED)
-    Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state)
+    Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
 
     notification.close_mr(merge_request, current_user)
   end
@@ -33,11 +35,13 @@ class MergeRequestObserver < ActivityObserver
 
   def after_reopen(merge_request, transition)
     create_event(merge_request, Event::REOPENED)
-    Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state)
+    Note.create_status_change_note(merge_request, merge_request.target_project, current_user, merge_request.state, nil)
   end
 
   def after_update(merge_request)
     notification.reassigned_merge_request(merge_request, current_user) if merge_request.is_being_reassigned?
+
+    merge_request.notice_added_references(merge_request.project, current_user)
   end
 
   def create_event(record, status)
diff --git a/app/observers/note_observer.rb b/app/observers/note_observer.rb
index 7b79161cce4..d31b6e8d7ce 100644
--- a/app/observers/note_observer.rb
+++ b/app/observers/note_observer.rb
@@ -1,5 +1,17 @@
 class NoteObserver < BaseObserver
   def after_create(note)
     notification.new_note(note)
+
+    unless note.system?
+      # Create a cross-reference note if this Note contains GFM that names an
+      # issue, merge request, or commit.
+      note.references.each do |mentioned|
+        Note.create_cross_reference_note(mentioned, note.noteable, note.author, note.project)
+      end
+    end
+  end
+
+  def after_update(note)
+    note.notice_added_references(note.project, current_user)
   end
 end