Add channel mode +u to hide banlists

Banlists are silently hidden from all non-halfops or up. Bans still may
be seen as normally. This mode is entirely opt-in.

help/opers/cmode

@@ -26,6 +26,8 @@ NO PARAMETERS:
               weakens +i control.
      +z     - Op moderated.  Messages blocked by +m, +b and +q are instead
               sent to ops.
+     +u     - Hidden ban/quiet list. Ban/quiet lists may only be seen
+              by halfops or higher.
    * +L     - Large ban list.  Increase maximum number of +beIq entries.
    * +P     - Permanent.  Channel does not disappear when empty.
      +F     - Free target.  Anyone may set forwards to this (otherwise

help/users/cmode

@@ -24,6 +24,8 @@ NO PARAMETERS:
               change nick.
      +g     - Free invite.  Everyone may invite users.  Significantly
               weakens +i control.
+     +u     - Hidden ban/quiet lists. Ban/quiet lists are hidden from all
+              channel members that are not a halfop or higher.
      +z     - Op moderated.  Messages blocked by +m, +b and +q are instead
               sent to ops.
    * +L     - Large ban list.  Increase maximum number of +beIq entries.

include/channel.h

@@ -191,6 +191,7 @@ typedef int (*ExtbanFunc)(const char *data, struct Client *client_p,
 #define MODE_NOREJOIN	0x200000 /* Block rejoin immediately after kick */
 #define MODE_NOREPEAT	0x400000 /* Block repeat messages */
 #define MODE_NOOPERKICK	0x800000 /* disallow kicking opers */
+#define MODE_HIDEBANS	0x1000000 /* disallow non-chanops from seeing ban/quiet lists */
 
 #define CHFL_BAN        0x10000000	/* ban channel flag */
 #define CHFL_EXCEPTION  0x20000000	/* exception to ban channel flag */

src/chmode.c

@@ -907,6 +907,7 @@ chm_ban(struct Client *source_p, struct Channel *chptr,
 			}
 		}
 
+		if(!(chptr->mode.mode & MODE_HIDEBANS) || alevel & ONLY_CHANOPS) {
 			RB_DLINK_FOREACH(ptr, list->head)
 			{
 				banptr = ptr->data;
@@ -914,6 +915,8 @@ chm_ban(struct Client *source_p, struct Channel *chptr,
 					   me.name, source_p->name, chptr->chname,
 					   banptr->banstr, banptr->who, banptr->when);
 			}
+		}
+
 		sendto_one(source_p, form_str(rpl_endlist), me.name, source_p->name, chptr->chname);
 		return;
 	}
@@ -2004,7 +2007,7 @@ struct ChannelMode chmode_table[256] =
   {chm_simple, MODE_REGONLY },		/* r */
   {chm_simple,	MODE_SECRET },		/* s */
   {chm_simple,	MODE_TOPICLIMIT },	/* t */
-  {chm_nosuch,	0 },			/* u */
+  {chm_simple,	MODE_HIDEBANS },	/* u */
   {chm_voice,	0 },			/* v */
   {chm_nosuch,	0 },			/* w */
   {chm_nosuch,	0 },			/* x */