Pre-selects values on issue and merge request dropdown

Closes #14290

app/helpers/issuables_helper.rb

@@ -20,6 +20,34 @@ module IssuablesHelper
     base_issuable_scope(issuable).where('iid < ?', issuable.iid).first
   end
 
+  def user_dropdown_label(user_id, default_label)
+    return "Unassigned" if user_id == "0"
+
+    user = @project.team.users.find_by(id: user_id)
+
+    if user
+      user.name
+    else
+      default_label
+    end
+  end
+
+  def labels_dropdown_label(label_name)
+    if !label_name
+      "Label"
+    else
+      label_name
+    end
+  end
+
+  def milestone_dropdown_label(milestone_name)
+    if !milestone_name
+      "Milestone"
+    else
+      milestone_name
+    end
+  end
+
   private
 
   def sidebar_gutter_collapsed?

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

@@ -9,19 +9,19 @@
         .filter-item.inline
           - if params[:author_id]
             = hidden_field_tag(:author_id, params[:author_id])
-          = dropdown_tag("Author", options: { toggle_class: "js-user-search js-filter-submit js-author-search", title: "Filter by author", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-author",
+          = dropdown_tag(user_dropdown_label(params[:author_id], "Author"), options: { toggle_class: "js-user-search js-filter-submit js-author-search", title: "Filter by author", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-author",
             placeholder: "Search authors", data: { any_user: "Any Author", first_user: (current_user.username if current_user), current_user: true, project_id: (@project.id if @project), selected: params[:author_id], field_name: "author_id" } })
 
         .filter-item.inline
           - if params[:assignee_id]
             = hidden_field_tag(:assignee_id, params[:assignee_id])
-          = dropdown_tag("Assignee", options: { toggle_class: "js-user-search js-filter-submit js-assignee-search", title: "Filter by assignee", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-assignee",
+          = dropdown_tag(user_dropdown_label(params[:assignee_id], "Assignee"), options: { toggle_class: "js-user-search js-filter-submit js-assignee-search", title: "Filter by assignee", filter: true, dropdown_class: "dropdown-menu-user dropdown-menu-selectable dropdown-menu-assignee",
             placeholder: "Search assignee", data: { any_user: "Any Assignee", first_user: (current_user.username if current_user), null_user: true, current_user: true, project_id: (@project.id if @project), selected: params[:assignee_id], field_name: "assignee_id" } })
 
         .filter-item.inline.milestone-filter
           - if params[:milestone_title]
             = hidden_field_tag(:milestone_title, params[:milestone_title])
-          = dropdown_tag("Milestone", 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(params[:milestone_title]), options: { title: "Filter by milestone", toggle_class: 'js-milestone-select js-filter-submit', filter: true, dropdown_class: "dropdown-menu-selectable",
             placeholder: "Search milestones", footer_content: true, data: { show_no: true, show_any: true, field_name: "milestone_title", selected: params[:milestone_title], project_id: (@project.id if @project), milestones: (namespace_project_milestones_path(@project.namespace, @project, :js) if @project) } }) do
             - if @project
               %ul.dropdown-footer-list
@@ -42,7 +42,7 @@
           .dropdown
             %button.dropdown-menu-toggle.js-label-select.js-filter-submit{type: "button", data: {toggle: "dropdown", field_name: "label_name", show_no: "true", show_any: "true", selected: params[:label_name], project_id: (@project.id if @project), labels: (namespace_project_labels_path(@project.namespace, @project, :js) if @project)}}
               %span.dropdown-toggle-text
-                Label
+                = labels_dropdown_label(params[:label_name])
               = icon('chevron-down')
             .dropdown-menu.dropdown-select.dropdown-menu-paging.dropdown-menu-labels.dropdown-menu-selectable
               .dropdown-page-one