Fix issue with milestone dropdown submitting the form without selected value

app/assets/javascripts/milestone_select.js.coffee

@@ -79,7 +79,7 @@ class @MilestoneSelect
         text: (milestone) ->
           _.escape(milestone.title)
         id: (milestone) ->
-          if !useId
+          if !useId and not $dropdown.is('.js-issuable-form-dropdown')
             milestone.name
           else
             milestone.id
@@ -90,12 +90,13 @@ class @MilestoneSelect
 
           # display:block overrides the hide-collapse rule
           $value.css('display', '')
-        clicked: (selected) ->
+        clicked: (selected, $el, e) ->
           page = $('body').data 'page'
           isIssueIndex = page is 'projects:issues:index'
           isMRIndex = page is page is 'projects:merge_requests:index'
 
-          if $dropdown.hasClass 'js-filter-bulk-update'
+          if $dropdown.hasClass('js-filter-bulk-update') or $dropdown.hasClass('js-issuable-form-dropdown')
+            e.preventDefault()
             return
 
           if $dropdown.hasClass('js-filter-submit') and (isIssueIndex or isMRIndex)

app/views/shared/issuable/_form.html.haml

@@ -61,7 +61,7 @@
         = f.label :milestone_id, "Milestone", class: "control-label #{"col-lg-4" if has_due_date}"
         .col-sm-10{ class: ("col-lg-8" if has_due_date) }
           .issuable-form-select-holder
-            = render "shared/issuable/milestone_dropdown", selected: issuable.milestone_id, name: "#{issuable.class.model_name.param_key}[milestone_id]", show_any: false, show_upcoming: false
+            = render "shared/issuable/milestone_dropdown", selected: issuable.milestone_id, name: "#{issuable.class.model_name.param_key}[milestone_id]", show_any: false, show_upcoming: false, extra_class: 'js-issuable-form-dropdown'
       .form-group
         - has_labels = issuable.project.labels.any?
         - selected_labels = issuable.label_ids.any? ? issuable.label_ids : nil

app/views/shared/issuable/_milestone_dropdown.html.haml

 - project = @target_project || @project
+- selected_text = project.milestones.find(selected).try(:name)
 - if selected.present?
   = hidden_field_tag(name, selected)
-= dropdown_tag(milestone_dropdown_label(selected), options: { title: "Filter by milestone", toggle_class: 'js-milestone-select js-filter-submit', filter: true, dropdown_class: "dropdown-menu-selectable",
+= dropdown_tag(milestone_dropdown_label(selected_text), options: { title: "Filter by milestone", toggle_class: "js-milestone-select js-filter-submit #{extra_class}", filter: true, dropdown_class: "dropdown-menu-selectable",
   placeholder: "Search milestones", footer_content: project.present?, data: { show_no: true, show_any: show_any, show_upcoming: show_upcoming, field_name: name, selected: selected, project_id: project.try(:id), milestones: milestones_filter_dropdown_path, default_label: "Milestone" } }) do
   - if project
     %ul.dropdown-footer-list