Don't allow deleting a ghost user.

- Add a `destroy_user` ability. This didn't exist before, and was implicit in
  other abilities (only admins could access the admin area, so only they could
  destroy all users; a user can only access their own account page, and so can
  destroy only themselves).

- Grant this ability to admins, and when the current user is trying to destroy
  themselves. Disallow destroying ghost users in all cases.

- Modify the `Users::DestroyService` to check this ability. Also check it in
  views to decide whether or not to show the "Delete User" button.

- Add a short summary of the Ghost User to the bio.

1 files changed, 8 insertions, 0 deletions

diff --git a/app/policies/user_policy.rb b/app/policies/user_policy.rb
index 03a2499e263..229846e368c 100644
--- a/app/policies/user_policy.rb
+++ b/app/policies/user_policy.rb
@@ -3,6 +3,14 @@ class UserPolicy < BasePolicy
 
   def rules
     can! :read_user if @user || !restricted_public_level?
+
+    if @user
+      if @user.admin? || @subject == @user
+        can! :destroy_user
+      end
+
+      cannot! :destroy_user if @subject.ghost?
+    end
   end
 
   def restricted_public_level?