(js) Restrict special mailboxes to the top level

Fixes #6963

NEWS

@@ -8,6 +8,7 @@ Enhancements
  - [web] constrain event/task reminder to a positive number
  - [web] display year in day and week views
  - [web] split string on comma and semicolon when pasting multiple addresses (#4097)
+ - [web] restrict Draft/Sent/Trash/Junk mailboxes to the top level (#6963)
 
 Bug fixes
  - [core] handle broken CalDAV clients sending bogus SENT-BY (#3992)

UI/Templates/MailerUI/UIxMailMainFrame.wox

@@ -161,23 +161,23 @@
                         <var:string label:value="Search"/>
                       </md-button>
                     </md-menu-item>
-                    <md-menu-divider ng-show="folder.type == 'folder'"><!-- divider --></md-menu-divider>
+                    <md-menu-divider ng-show="folder.$canFolderAs()"><!-- divider --></md-menu-divider>
                     <md-menu-item ng-show="folder.type == 'folder'">
                       <md-button type="button" ng-click="app.setFolderAs(folder, 'Drafts')">
                         <var:string label:value="Set as Drafts"/>
                       </md-button>
                     </md-menu-item>
-                    <md-menu-item ng-show="folder.type == 'folder'">
+                    <md-menu-item ng-show="folder.$canFolderAs()">
                       <md-button type="button" ng-click="app.setFolderAs(folder, 'Sent')">
                         <var:string label:value="Set as Sent"/>
                       </md-button>
                     </md-menu-item>
-                    <md-menu-item ng-show="folder.type == 'folder'">
+                    <md-menu-item ng-show="folder.$canFolderAs()">
                       <md-button type="button" ng-click="app.setFolderAs(folder, 'Trash')">
                         <var:string label:value="Set as Trash"/>
                       </md-button>
                     </md-menu-item>
-                    <md-menu-item ng-show="folder.type == 'folder'">
+                    <md-menu-item ng-show="folder.$canFolderAs()">
                       <md-button type="button" ng-click="app.setFolderAs(folder, 'Junk')">
                         <var:string label:value="Set as Junk"/>
                       </md-button>

UI/WebServerResources/js/Mailer/Mailbox.service.js

@@ -571,6 +571,16 @@
       });
   };
 
+  /**
+   * @function $canFolderAs
+   * @memberof Mailbox.prototype
+   * @desc Check if the folder can be set as Drafts/Sent/Trash
+   * @returns true if folder is eligible
+   */
+  Mailbox.prototype.$canFolderAs = function() {
+    return this.type == 'folder' && this.level === 0;
+  };
+
   /**
    * @function $setFolderAs
    * @memberof Mailbox.prototype