Merge branch 'label-filter-fix' into 'master'

Fixed issue where label filtering didnt work

## What does this MR do?

The filterable option was missing which meant labels in the dropdown couldn't be filtered. This fixes that.

## What are the relevant issue numbers?

Closes #18375 

See merge request !4556

app/assets/javascripts/labels_select.js.coffee

@@ -254,7 +254,7 @@ class @LabelsSelect
         search:
           fields: ['title']
         selectable: true
-
+        filterable: true
         toggleLabel: (selected, el) ->
           selected_labels = $('.js-label-select').siblings('.dropdown-menu-labels').find('.is-active')
 

app/helpers/dropdowns_helper.rb

@@ -67,9 +67,9 @@ module DropdownsHelper
     end
   end
 
-  def dropdown_filter(placeholder)
+  def dropdown_filter(placeholder, search_id: nil)
     content_tag :div, class: "dropdown-input" do
-      filter_output = search_field_tag nil, nil, class: "dropdown-input-field", placeholder: placeholder
+      filter_output = search_field_tag search_id, nil, class: "dropdown-input-field", placeholder: placeholder
       filter_output << icon('search', class: "dropdown-input-search")
       filter_output << icon('times', class: "dropdown-input-clear js-dropdown-input-clear", role: "button")
 

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

@@ -4,7 +4,7 @@
 - filter_placeholder = local_assigns.fetch(:filter_placeholder, 'Search labels')
 .dropdown-page-one
   = dropdown_title(title)
-  = dropdown_filter(filter_placeholder)
+  = dropdown_filter(filter_placeholder, search_id: "label-name")
   = dropdown_content
   - if @project && show_footer
     = dropdown_footer do

spec/features/issues/filter_by_labels_spec.rb

@@ -199,4 +199,19 @@ feature 'Issue filtering by Labels', feature: true do
       end
     end
   end
+
+  context 'dropdown filtering', js: true do
+    it 'should filter by label name' do
+      page.within '.labels-filter' do
+        click_button 'Label'
+        wait_for_ajax
+        fill_in 'label-name', with: 'bug'
+
+        page.within '.dropdown-content' do
+          expect(page).not_to have_content 'enhancement'
+          expect(page).to have_content 'bug'
+        end
+      end
+    end
+  end
 end