backend completely drives creation of merge commit message

app/models/merge_request.rb

@@ -628,7 +628,7 @@ class MergeRequest < ActiveRecord::Base
     self.target_project.repository.branch_names.include?(self.target_branch)
   end
 
-  def merge_commit_message
+  def merge_commit_message(include_description: false)
     closes_issues_references = closes_issues.map do |issue|
       issue.to_reference(target_project)
     end
@@ -640,6 +640,7 @@ class MergeRequest < ActiveRecord::Base
       message << "Closed Issues: #{closes_issues_references.join(", ")}\n\n"
     end
 
+    message << "#{description}\n\n" if include_description && description.present?
     message << "See merge request #{to_reference}"
 
     message

app/views/projects/merge_requests/widget/_open.html.haml

@@ -37,12 +37,11 @@
         #{"Issue".pluralize(mr_issues_mentioned_but_not_closing.size)} mentioned but not being closed:
         = succeed '.' do
           != markdown issues_sentence(mr_issues_mentioned_but_not_closing), pipeline: :gfm, author: @merge_request.author
-        = mr_assign_issues_link
 
   - if mr_closes_issues.present?
     .mr-widget-footer
       %span
-        %i.fa.fa-check
+        = icon('check')
         Accepting this merge request will close #{"issue".pluralize(mr_closes_issues.size)}
         = succeed '.' do
           != markdown issues_sentence(mr_closes_issues), pipeline: :gfm, author: @merge_request.author

app/views/projects/merge_requests/widget/open/_accept.html.haml

@@ -41,7 +41,8 @@
           Modify commit message
     .js-toggle-content.hide.prepend-top-default
       = render 'shared/commit_message_container', params: params,
-          description: @merge_request.description,
+          message_with_description: @merge_request.merge_commit_message(include_description: true),
+          message_without_description: @merge_request.merge_commit_message,
           text: @merge_request.merge_commit_message,
           rows: 14, hint: true
 

app/views/shared/_commit_message_container.html.haml

@@ -8,42 +8,38 @@
       = text_area_tag 'commit_message',
           (params[:commit_message] || local_assigns[:text] || local_assigns[:placeholder]),
           class: 'form-control js-commit-message', placeholder: local_assigns[:placeholder],
+          data: local_assigns.slice(:message_with_description, :message_without_description),
           required: true, rows: (local_assigns[:rows] || 3),
           id: "commit_message-#{nonce}"
     - if local_assigns[:hint]
       %p.hint
         Try to keep the first line under 52 characters
         and the others under 72.
-    - if local_assigns[:description] 
-      %p.hint.use-description-hint
-        = link_to "#", class: "use-description-link" do
-          Use Merge Request description as merge commit message
-      %p.hint.use-default-message-hint.hide
-        = link_to "#", class: "use-default-message-link" do
-          Use default Gitlab merge commit message
+    -if local_assigns.slice(:message_with_description, :message_without_description).present?
+      %p.hint.with-description-hint
+        = link_to "#", class: "with-description-link" do
+          Include description in commit message
+      %p.hint.without-description-hint.hide
+        = link_to "#", class: "without-description-link" do
+          Don't include description in commit message
 
       :javascript
-        $('.use-description-link').on('click', function(e) {
+        $('.with-description-link').on('click', function(e) {
           e.preventDefault();
 
-          var message = "Merge branch '#{j @merge_request.source_branch}' into '#{j @merge_request.target_branch}'\n\n"
-          message = message + "#{j @merge_request.title}\n\n"
-          message = message + "#{j local_assigns[:description]}\n\n";
-          message = message + "See merge request #{j @merge_request.to_reference}"
+          var textarea = $('.js-commit-message')
 
-
-          $('.use-description-hint').hide();
-          $('.use-default-message-hint').show();
-          $('.js-commit-message').val(message)
+          textarea.val(textarea.data('messageWithDescription'))
+          $('.with-description-hint').hide();
+          $('.without-description-hint').show();
         });
 
-        $('.use-default-message-link').on('click', function(e) {
+        $('.without-description-link').on('click', function(e) {
           e.preventDefault();
 
-          var defaultMessage = "#{j (params[:commit_message] || local_assigns[:text] || local_assigns[:placeholder])}";
+          var textarea = $('.js-commit-message')
 
-          $('.use-description-hint').show();
-          $('.use-default-message-hint').hide();
-          $('.js-commit-message').val(defaultMessage);
+          textarea.val(textarea.data('messageWithoutDescription'))
+          $('.with-description-hint').show();
+          $('.without-description-hint').hide();
         });
-

spec/models/merge_request_spec.rb

@@ -440,6 +440,20 @@ describe MergeRequest, models: true do
 
       expect(request.merge_commit_message).not_to match("Title\n\n\n\n")
     end
+
+    it 'includes its description in the body' do
+      request = build(:merge_request, description: 'By removing all code')
+
+      expect(request.merge_commit_message(include_description: true))
+        .to match("By removing all code\n\n")
+    end
+
+    it 'does not includes its description in the body' do
+      request = build(:merge_request, description: 'By removing all code')
+
+      expect(request.merge_commit_message)
+        .not_to match("By removing all code\n\n")
+    end
   end
 
   describe "#reset_merge_when_build_succeeds" do