Prevent click from propagating to parent

Prevent Edit button click event from propagating further up which makes
datepicker hide immediately as soon as it shows up.

ee/app/assets/javascripts/epic/components/sidebar_items/sidebar_date_picker.vue

@@ -171,8 +171,9 @@ export default {
       this.editing = false;
       this.$emit('toggleDateType', true, true);
     },
-    toggleDatePicker() {
+    toggleDatePicker(e) {
       this.editing = !this.editing;
+      e.stopPropagation();
     },
     newDateSelected(date = null) {
       this.editing = false;

ee/spec/features/epics/update_epic_spec.rb

@@ -121,6 +121,16 @@ describe 'Update Epic', :js do
       end
     end
 
+    context 'epic sidebar' do
+      it 'opens datepicker when clicking Edit button' do
+        page.within('.issuable-sidebar .block.start-date') do
+          click_button('Edit')
+          expect(find('.value-type-fixed')).to have_selector('.pikaday-container')
+          expect(find('.value-type-fixed')).to have_selector('.pikaday-container .pika-single.is-bound')
+        end
+      end
+    end
+
     it 'updates the tasklist' do
       expect(page).to have_selector('ul.task-list',      count: 1)
       expect(page).to have_selector('li.task-list-item', count: 1)

ee/spec/javascripts/epic/components/sidebar_items/sidebar_date_picker_spec.js

@@ -169,10 +169,14 @@ describe('SidebarDatePicker', () => {
 
     describe('toggleDatePicker', () => {
       it('flips value of `editing` prop from `true` to `false` and vice-versa', () => {
+        const e = new Event('click');
+        spyOn(e, 'stopPropagation');
+
         vm.editing = true;
-        vm.toggleDatePicker();
+        vm.toggleDatePicker(e);
 
         expect(vm.editing).toBe(false);
+        expect(e.stopPropagation).toHaveBeenCalled();
       });
     });