Add comment to merge request when new push happens

It allows track when user added new commits to existing merge request
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/note.rb

@@ -117,6 +117,24 @@ class Note < ActiveRecord::Base
       })
     end
 
+    def create_new_commits_note(noteable, project, author, commits)
+      body = "Pushed new commits:\n\n"
+
+      commits.each do |commit|
+        message = "* #{commit.short_id} - #{commit.title}"
+        body << message
+        body << "\n"
+      end
+
+      create(
+        noteable: noteable,
+        project: project,
+        author: author,
+        note: body,
+        system: true
+      )
+    end
+
     def discussions_from_notes(notes)
       discussion_ids = []
       discussions = []

app/models/project.rb

@@ -400,18 +400,35 @@ class Project < ActiveRecord::Base
   def update_merge_requests(oldrev, newrev, ref, user)
     return true unless ref =~ /heads/
     branch_name = ref.gsub("refs/heads/", "")
-    c_ids = self.repository.commits_between(oldrev, newrev).map(&:id)
+    commits = self.repository.commits_between(oldrev, newrev)
+    c_ids = commits.map(&:id)
 
     # Close merge requests
     mrs = self.merge_requests.opened.where(target_branch: branch_name).to_a
     mrs = mrs.select(&:last_commit).select { |mr| c_ids.include?(mr.last_commit.id) }
-    mrs.each { |merge_request| MergeRequests::MergeService.new.execute(merge_request, user, nil) }
+
+    mrs.uniq.each do |merge_request|
+      MergeRequests::MergeService.new.execute(merge_request, user, nil)
+    end
 
     # Update code for merge requests into project between project branches
     mrs = self.merge_requests.opened.by_branch(branch_name).to_a
     # Update code for merge requests between project and project fork
     mrs += self.fork_merge_requests.opened.by_branch(branch_name).to_a
-    mrs.each { |merge_request| merge_request.reload_code; merge_request.mark_as_unchecked }
+
+    mrs.uniq.each do |merge_request|
+      merge_request.reload_code
+      merge_request.mark_as_unchecked
+    end
+
+    # Add comment about pushing new commits to merge requests
+    mrs = self.merge_requests.opened.where(source_branch: branch_name).to_a
+    mrs += self.fork_merge_requests.opened.where(source_branch: branch_name).to_a
+
+    mrs.uniq.each do |merge_request|
+      Note.create_new_commits_note(merge_request, merge_request.project,
+                                   user, commits)
+    end
 
     true
   end