FEATURE: Add new API to add a toolbar popup menu button.

app/assets/javascripts/discourse/controllers/composer.js.es6

@@ -42,6 +42,12 @@ function loadDraft(store, opts) {
   }
 }
 
+const _popupMenuOptionsCallbacks = [];
+
+export function addPopupMenuOptionsCallback(callback) {
+  _popupMenuOptionsCallbacks.push(callback);
+}
+
 export default Ember.Controller.extend({
   needs: ['modal', 'topic', 'application'],
   replyAsNewTopicDraft: Em.computed.equal('model.draftKey', Composer.REPLY_AS_NEW_TOPIC_KEY),
@@ -56,6 +62,20 @@ export default Ember.Controller.extend({
   topic: null,
   linkLookup: null,
 
+  init() {
+    this._super();
+    const self = this
+
+    addPopupMenuOptionsCallback(function() {
+      return {
+        action: 'toggleWhisper',
+        icon: 'eye-slash',
+        label: 'composer.toggle_whisper',
+        condition: "canWhisper"
+      };
+    });
+  },
+
   showToolbar: Em.computed({
     get(){
       const keyValueStore = this.container.lookup('key-value-store:main');
@@ -92,6 +112,25 @@ export default Ember.Controller.extend({
     return currentUser && currentUser.get('staff') && this.siteSettings.enable_whispers && action === Composer.REPLY;
   },
 
+  @computed("model.composeState")
+  popupMenuOptions(composeState) {
+    const self = this;
+
+    if (composeState === 'open') {
+      return _popupMenuOptionsCallbacks.map(callback => {
+        let option = callback();
+
+        if (option.condition) {
+          option.condition = self.get(option.condition);
+        } else {
+          option.condition = true;
+        }
+
+        return option;
+      });
+    }
+  },
+
   showWarning: function() {
     if (!Discourse.User.currentProp('staff')) { return false; }
 

app/assets/javascripts/discourse/lib/plugin-api.js.es6

@@ -10,6 +10,7 @@ import { onPageChange } from 'discourse/lib/page-tracker';
 import { preventCloak } from 'discourse/widgets/post-stream';
 import { h } from 'virtual-dom';
 import { addFlagProperty } from 'discourse/components/site-header';
+import { addPopupMenuOptionsCallback } from 'discourse/controllers/composer';
 
 class PluginApi {
   constructor(version, container) {
@@ -224,6 +225,26 @@ class PluginApi {
     addToolbarCallback(callback);
   }
 
+  /**
+   * Add a new button in the options popup menu.
+   *
+   * Example:
+   *
+   * ```
+   * api.addToolbarPopupMenuOptionsCallback(function(controller) {
+   *  return {
+   *    action: 'toggleWhisper',
+   *    icon: 'eye-slash',
+   *    label: 'composer.toggle_whisper',
+   *    condition: "canWhisper"
+   *  };
+   * });
+   * ```
+  **/
+  addToolbarPopupMenuOptionsCallback(callback) {
+    addPopupMenuOptionsCallback(callback);
+  }
+
   /**
    * A hook that is called when the post stream is removed from the DOM.
    * This advanced hook should be used if you end up wiring up any

app/assets/javascripts/discourse/templates/composer.hbs

@@ -3,9 +3,13 @@
 
   {{#if currentUser.staff}}
     {{#popup-menu visible=optionsVisible hide="hideOptions" title="composer.options"}}
-      <li>
-        {{d-button action="toggleWhisper" icon="eye-slash" label="composer.toggle_whisper"}}
-      </li>
+      {{#each popupMenuOptions as |option|}}
+        {{#if option.condition}}
+          <li>
+          {{d-button action=option.action icon=option.icon label=option.label}}
+          </li>
+        {{/if}}
+      {{/each}}
     {{/popup-menu}}
   {{/if}}