Error message from trac-admin is ambiguous when permission can't be removed

[Ryan J Ollos]

The following was discussed this evening on IRC. Suppose I have a default Trac installation and assign an arbitrarily-chosen permission to a new user:

$ trac-admin tracdev permission add user1 WIKI_DELETE

Listing the permissions for that user, it appears they have WIKI_VIEW:

$ trac-admin ../tracdev permission list user1

User   Action                 
------------------------------
user1  BROWSER_VIEW           
user1  CHANGESET_VIEW         
user1  CONFIG_VIEW            
user1  EMAIL_VIEW             
user1  FILE_VIEW              
user1  LOG_VIEW               
user1  MILESTONE_ADMIN        
user1  MILESTONE_CREATE       
user1  MILESTONE_DELETE       
user1  MILESTONE_MODIFY       
user1  MILESTONE_VIEW         
user1  PERMISSION_ADMIN       
user1  PERMISSION_GRANT       
user1  PERMISSION_REVOKE      
user1  REPORT_ADMIN           
user1  REPORT_CREATE          
user1  REPORT_DELETE          
user1  REPORT_MODIFY          
user1  REPORT_SQL_VIEW        
user1  REPORT_VIEW            
user1  ROADMAP_ADMIN          
user1  ROADMAP_VIEW           
user1  SEARCH_VIEW            
user1  TICKET_ADMIN           
user1  TICKET_APPEND          
user1  TICKET_BATCH_MODIFY    
user1  TICKET_CHGPROP         
user1  TICKET_CREATE          
user1  TICKET_EDIT_CC         
user1  TICKET_EDIT_COMMENT    
user1  TICKET_EDIT_DESCRIPTION
user1  TICKET_MODIFY          
user1  TICKET_VIEW            
user1  TIMELINE_VIEW          
user1  TRAC_ADMIN             
user1  VERSIONCONTROL_ADMIN   
user1  WIKI_ADMIN             
user1  WIKI_CREATE            
user1  WIKI_DELETE            
user1  WIKI_MODIFY            
user1  WIKI_RENAME            
user1  WIKI_VIEW              

However, it is not possible to remove the permission:

$ trac-admin ../tracdev permission remove user1 WIKI_VIEW
Error: Cannot remove permission WIKI_VIEW for user user1.

This is because the permission is assigned to the anonymous group:

$ trac-admin ../tracdev permission list anonymous

User       Action                 
----------------------------------
anonymous  BROWSER_VIEW           
anonymous  CHANGESET_VIEW         
anonymous  CONFIG_VIEW            
anonymous  EMAIL_VIEW             
anonymous  FILE_VIEW              
anonymous  LOG_VIEW               
anonymous  MILESTONE_ADMIN        
anonymous  MILESTONE_CREATE       
anonymous  MILESTONE_DELETE       
anonymous  MILESTONE_MODIFY       
anonymous  MILESTONE_VIEW         
anonymous  PERMISSION_ADMIN       
anonymous  PERMISSION_GRANT       
anonymous  PERMISSION_REVOKE      
anonymous  REPORT_ADMIN           
anonymous  REPORT_CREATE          
anonymous  REPORT_DELETE          
anonymous  REPORT_MODIFY          
anonymous  REPORT_SQL_VIEW        
anonymous  REPORT_VIEW            
anonymous  ROADMAP_ADMIN          
anonymous  ROADMAP_VIEW           
anonymous  SEARCH_VIEW            
anonymous  TICKET_ADMIN           
anonymous  TICKET_APPEND          
anonymous  TICKET_BATCH_MODIFY    
anonymous  TICKET_CHGPROP         
anonymous  TICKET_CREATE          
anonymous  TICKET_EDIT_CC         
anonymous  TICKET_EDIT_COMMENT    
anonymous  TICKET_EDIT_DESCRIPTION
anonymous  TICKET_MODIFY          
anonymous  TICKET_VIEW            
anonymous  TIMELINE_VIEW          
anonymous  TRAC_ADMIN             
anonymous  VERSIONCONTROL_ADMIN   
anonymous  WIKI_ADMIN             
anonymous  WIKI_CREATE            
anonymous  WIKI_DELETE            
anonymous  WIKI_MODIFY            
anonymous  WIKI_RENAME            
anonymous  WIKI_VIEW              

We should at least try to provide an indication of why the permission can't be removed from the user