Restrict mentions to users who have permission to view current page

Problem Definition

User mentioning is possible for any users on the instance, regardless of the page you are mentioning on. This causes a problem if you've mentioned someone but they don't have permissions to see the page, and so they won't see your comments. The user does not get any notifications.

Suggested Solution

• Either show a warning that the user does not have permission to view the page
• Or only list the users that are able to view. First option is probably better.

 h3. Workaround
Go to ... > People who can view for a simple list of all the people who:

• are allowed to view the space, via space permissions, and
• are not prevented from viewing the page by page restrictions.