Remove `Add Issues` button and a related modal

app/assets/javascripts/boards/index.js

@@ -306,7 +306,7 @@ export default () => {
 
   const issueBoardsModal = document.getElementById('js-add-issues-btn');
 
-  if (issueBoardsModal) {
+  if (issueBoardsModal && gon.features.addIssuesButton) {
     // eslint-disable-next-line no-new
     new Vue({
       el: issueBoardsModal,

app/controllers/projects/boards_controller.rb

@@ -7,6 +7,9 @@ class Projects::BoardsController < Projects::ApplicationController
   before_action :check_issues_available!
   before_action :authorize_read_board!, only: [:index, :show]
   before_action :assign_endpoint_vars
+  before_action do
+    push_frontend_feature_flag(:add_issues_button)
+  end
 
   feature_category :boards
 

changelogs/unreleased/284070-issue-list-dropdown-not-shown-in-boards-add-issue-modal.yml

+---
+title: Remove `Add Issues` button and a related modal
+merge_request: 47898
+author:
+type: changed

config/feature_flags/development/add_issues_button.yml

+---
+name: add_issues_button
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47898
+rollout_issue_url:
+milestone: '13.6'
+type: development
+group: group::project management
+default_enabled: false

doc/user/project/issue_board.md

@@ -433,7 +433,13 @@ To remove a list from an issue board:
 1. Select **Remove list**. A confirmation dialog appears.
 1. Select **OK**.
 
-### Add issues to a list
+### Add issues to a list **(CORE ONLY)**
+
+> - Feature flag [introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47898) in GitLab 13.7.
+> - It's [deployed behind a feature flag](../feature_flags.md), disabled by default.
+> - It's disabled on GitLab.com.
+> - It's recommended for production use.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-adding-issues-to-the-list). **(CORE ONLY)**
 
 You can add issues to a list in a project issue board by clicking the **Add issues** button
 in the top right corner of the issue board. This opens up a modal
@@ -453,7 +459,23 @@ the list by filtering by the following:
 - Release
 - Weight
 
-![Bulk adding issues to lists](img/issue_boards_add_issues_modal_v13_6.png)
+#### Enable or disable adding issues to the list **(CORE ONLY)**
+
+Adding issues to the list is deployed behind a feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../administration/feature_flags.md)
+can enable it.
+
+To enable it:
+
+```ruby
+Feature.enable(:add_issues_button)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:add_issues_button)
+```
 
 ### Remove an issue from a list
 

ee/spec/features/boards/add_issues_modal_spec.rb

@@ -12,6 +12,7 @@ RSpec.describe 'Issue Boards add issue modal', :js do
   let!(:issue) { create(:issue, project: project, title: 'abc', description: 'def') }
 
   before do
+    stub_feature_flags(add_issues_button: true)
     project.add_maintainer(user)
 
     sign_in(user)

spec/features/boards/add_issues_modal_spec.rb

@@ -37,6 +37,10 @@ RSpec.describe 'Issue Boards add issue modal', :js do
   end
 
   context 'modal interaction' do
+    before do
+      stub_feature_flags(add_issues_button: true)
+    end
+
     it 'opens modal' do
       click_button('Add issues')
 
@@ -72,6 +76,7 @@ RSpec.describe 'Issue Boards add issue modal', :js do
 
   context 'issues list' do
     before do
+      stub_feature_flags(add_issues_button: true)
       click_button('Add issues')
 
       wait_for_requests