Allow WP_User->has_cap() to accept TRUE or FALSE as capability

[coffee2code]

It would be handy (and in some instances potentially eliminate some redundancy) if WP_User->has_cap() could be made to immediately return TRUE or FALSE if passed a boolean as the capability. The primary use case for this is for invoking the various menu-adding functions (add_menu_page(), add_submenu_page(), etc) after having determined the current user already has sufficient capabilities to view the menu. In such cases, we can bypass any further capability checks and simply pass TRUE or FALSE as the capability.

A simplistic example:

   if ( current_user_can( 'manage_options' ) ) {
      add_options_page( 'My Plugin', 'Item A', 'manage_options', 'my-plugin-a', array( &$this, 'my_menu_a' ) );
      add_options_page( 'My Plugin', 'Item B', 'manage_options', 'my-plugin-b', array( &$this, 'my_menu_b' ) );
      // do some other stuff here for someone with 'manage_options' capabilities
   }

In the above, the current user is being checked three times for the 'manage_options' capability. With the attached patch applied, it'd be:

   if ( current_user_can( 'manage_options' ) ) {
      add_options_page( 'My Plugin', 'Item A', true, 'my-plugin-a', array( &$this, 'my_menu_a' ) );
      add_options_page( 'My Plugin', 'Item B', true, 'my-plugin-b', array( &$this, 'my_menu_b' ) );
      // do some other stuff here for someone with 'manage_options' capabilities
   }

The patch should allow for a boolean to be specified as a capability in any capability-accepting function. If true or false is a capability (or in the list of capabilities), then has_cap() will return that boolean without further capability checking. In the event a capabilities array contains both, false takes precendence over true (err on the side of restriction rather than permission).

Patch attached.

Aforementioned patch.

I think that introduces bugs as it can differ on runtime. You seem to have a faible to overload function arguments, but I don't think that this is helpful generally.

Probably the information stored with the menu elements which capabilities are needed will be executed for other users as well which would return true for them even if they don't have the needed capability. That could be somehow dangerous and hard to debug.

Cap checks are very fast.

Agreed. This leaves room for error.