Added auto-subscribe newsletter count when confirming newsletter creation

refs https://github.com/TryGhost/Team/issues/1528

- used the already-loaded newsletters list to pass the slugs of active newsletters to the confirm modal, this allows use of the `{{members-count-fetcher}}` resource with the query `/members/?filter=newsletters:[...slugs]` to fetch a member and full count metadata
- added inclusion of `{{join}}` helper from `ember-composable-helpers` addon

ghost/admin/app/components/modals/edit-newsletter.js

@@ -8,6 +8,7 @@ import {tracked} from '@glimmer/tracking';
 
 export default class EditNewsletterModal extends Component {
     @service modals;
+    @service store;
 
     static modalOptions = {
         className: 'fullscreen-modal-full-overlay fullscreen-modal-portal-settings'
@@ -16,6 +17,14 @@ export default class EditNewsletterModal extends Component {
     @tracked tab = 'settings';
     @tracked optInExisting = this.args.data.newsletter.isNew;
 
+    get activeNewsletterSlugs() {
+        const activeNewsletters = this.store.peekAll('newsletter').filter((n) => {
+            return n.status === 'active' && !n.isNew && !n.isDestroyed;
+        });
+
+        return activeNewsletters.map(n => n.slug);
+    }
+
     willDestroy() {
         super.willDestroy(...arguments);
         this.args.data.newsletter.rollbackAttributes();
@@ -48,7 +57,8 @@ export default class EditNewsletterModal extends Component {
 
             const shouldCreate = yield this.modals.open(ConfirmCreateModal, {
                 optInExisting,
-                newsletter: this.args.data.newsletter
+                newsletter: this.args.data.newsletter,
+                activeNewsletterSlugs: this.activeNewsletterSlugs
             });
 
             if (!shouldCreate) {

ghost/admin/app/components/modals/edit-newsletter/confirm-create.hbs

@@ -7,17 +7,12 @@
     <div class="modal-body">
         <p>
             {{#if @data.optInExisting}}
-                {{!-- TODO: add members count once API supports it --}}
-                {{!-- {{#let (members-count-fetcher query=(hash filter="")) as |countFetcher|}}
+                {{#let (members-count-fetcher query=(hash filter=(concat "newsletters:[" (join @data.activeNewsletterSlugs ", ") "]"))) as |countFetcher|}}
                     Your newsletter <strong>{{@data.newsletter.name}}</strong> will be
                     immediately made live and your
                     {{#if countFetcher.count}}<strong>{{countFetcher.count}}</strong>{{/if}}
                     existing newsletter subscribers will be automatically opted-in to receive it.
-                {{/let}} --}}
-
-                Your newsletter <strong>{{@data.newsletter.name}}</strong> will be
-                immediately made live and your existing newsletter subscribers
-                will be automatically opted-in to receive it.
+                {{/let}}
             {{else}}
                 Your newsletter <strong>{{@data.newsletter.name}}</strong> will be
                 immediately made live. Your existing newsletter subscribers will

ghost/admin/ember-cli-build.js

@@ -117,7 +117,7 @@ module.exports = function (defaults) {
             includePolyfill: false
         },
         'ember-composable-helpers': {
-            only: ['optional', 'pick', 'toggle', 'toggle-action']
+            only: ['join', 'optional', 'pick', 'toggle', 'toggle-action']
         },
         'ember-promise-modals': {
             excludeCSS: true