Make milestone search async

Adds async search support within milestone select
dropdown.

app/assets/javascripts/milestone_select.js

@@ -76,6 +76,10 @@ export default class MilestoneSelect {
           let getMilestones = Api.projectMilestones;
           const reqParams = { state: 'active', include_parent_milestones: true };
 
+          if (term) {
+            reqParams.search = term.trim();
+          }
+
           if (!contextId) {
             contextId = $dropdown.get(0).dataset.groupId;
             delete reqParams.include_parent_milestones;
@@ -162,6 +166,7 @@ export default class MilestoneSelect {
         `;
         },
         filterable: true,
+        filterRemote: true,
         search: {
           fields: ['title'],
         },

spec/features/issues/user_edits_issue_spec.rb

@@ -4,13 +4,17 @@ require "spec_helper"
 
 RSpec.describe "Issues > User edits issue", :js do
   let_it_be(:project) { create(:project_empty_repo, :public) }
+  let_it_be(:project_with_milestones) { create(:project_empty_repo, :public) }
   let_it_be(:user) { create(:user) }
   let_it_be(:issue) { create(:issue, project: project, author: user, assignees: [user]) }
+  let_it_be(:issue_with_milestones) { create(:issue, project: project_with_milestones, author: user, assignees: [user]) }
   let_it_be(:label) { create(:label, project: project) }
   let_it_be(:milestone) { create(:milestone, project: project) }
+  let_it_be(:milestones) { create_list(:milestone, 25, project: project_with_milestones) }
 
   before do
     project.add_developer(user)
+    project_with_milestones.add_developer(user)
     sign_in(user)
   end
 
@@ -218,6 +222,23 @@ RSpec.describe "Issues > User edits issue", :js do
             end
           end
         end
+
+        it 'allows user to search milestone' do
+          visit project_issue_path(project_with_milestones, issue_with_milestones)
+
+          page.within('.milestone') do
+            click_link 'Edit'
+            wait_for_requests
+            # We need to enclose search string in quotes for exact match as all the milestone titles
+            # within tests are prefixed with `My title`.
+            find('.dropdown-input-field', visible: true).send_keys "\"#{milestones[0].title}\""
+            wait_for_requests
+
+            page.within '.dropdown-content' do
+              expect(page).to have_content milestones[0].title
+            end
+          end
+        end
       end
 
       context 'by unauthorized user' do