Disable 'Save changes' button if input is empty, fixes #6351

app/assets/javascripts/notes.js.coffee

@@ -321,7 +321,9 @@ class Notes
     GitLab.GfmAutoComplete.setup()
     form = note.find(".note-edit-form")
     form.show()
-    form.find("textarea").focus()
+    textarea = form.find("textarea")
+    textarea.focus()
+    disableButtonIfEmptyField textarea, form.find(".js-comment-button")
 
   ###
   Called in response to clicking the edit note link

app/views/projects/notes/_note.html.haml

@@ -38,10 +38,10 @@
         = f.text_area :note, class: 'note_text js-note-text js-gfm-input turn-on'
 
         .form-actions.clearfix
-          = f.submit 'Save changes', class: "btn btn-primary btn-save"
+          = f.submit 'Save changes', class: "btn btn-primary btn-save js-comment-button"
 
           .note-form-option
-            %a.choose-btn.btn.btn-small.js-choose-note-attachment-button
+            %a.choose-btn.btn.js-choose-note-attachment-button
               %i.icon-paper-clip
               %span Choose File ...