Update draft/rename implementation

Link to the new draft PR:
<https://github.com/ircv3/ircv3-specifications/pull/420>

Changes in the spec:

- Use standard replies instead of numerics:
  <https://github.com/ircv3/ircv3-specifications/pull/420/files#diff-70e90beef48dc9cf5d784d1e179ea822R44>
- Allow RENAME to a different case:
  <https://github.com/ircv3/ircv3-specifications/pull/420/files#diff-70e90beef48dc9cf5d784d1e179ea822R42>

This commit makes oragono send the PART-JOIN fallback even on case-only
changes. This is so that clients don't have to worry about oragono's
UTF8 casefolding. See the following comments for further info:
<https://github.com/ircv3/ircv3-specifications/pull/420#issuecomment-668770837>

Misc fixes:

- Remove unused variable,
- Add missing calls to utils.SafeErrorParam,
- Don't fill replies with the user-provided "oldName", for the same
  reason as sending the PART-JOIN fallback.

irc/channelmanager.go

@@ -287,6 +287,14 @@ func (cm *ChannelManager) Rename(name string, newName string) (err error) {
 	cm.Lock()
 	defer cm.Unlock()
 
+	if newCfname == cfname {
+		entry := cm.chans[cfname]
+		if entry == nil || !entry.channel.IsLoaded() {
+			return errNoSuchChannel
+		}
+		entry.channel.Rename(newName, cfname)
+		return nil
+	}
 	if cm.chans[newCfname] != nil || cm.registeredChannels.Has(newCfname) {
 		return errChannelNameInUse
 	}

irc/getters.go

@@ -453,9 +453,11 @@ func (channel *Channel) NameCasefolded() string {
 func (channel *Channel) Rename(name, nameCasefolded string) {
 	channel.stateMutex.Lock()
 	channel.name = name
-	channel.nameCasefolded = nameCasefolded
-	if channel.registeredFounder != "" {
-		channel.registeredTime = time.Now().UTC()
+	if channel.nameCasefolded != nameCasefolded {
+		channel.nameCasefolded = nameCasefolded
+		if channel.registeredFounder != "" {
+			channel.registeredTime = time.Now().UTC()
+		}
 	}
 	channel.stateMutex.Unlock()
 }

irc/handlers.go

@@ -2421,8 +2421,7 @@ func rehashHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *Re
 }
 
 // RENAME <oldchan> <newchan> [<reason>]
-func renameHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *ResponseBuffer) (result bool) {
-	result = false
+func renameHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *ResponseBuffer) bool {
 	oldName, newName := msg.Params[0], msg.Params[1]
 	var reason string
 	if 2 < len(msg.Params) {
@@ -2434,6 +2433,8 @@ func renameHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *Re
 		rb.Add(nil, server.name, ERR_NOSUCHCHANNEL, client.Nick(), utils.SafeErrorParam(oldName), client.t("No such channel"))
 		return false
 	}
+	oldName = channel.Name()
+
 	if !(channel.ClientIsAtLeast(client, modes.ChannelOperator) || client.HasRoleCapabs("chanreg")) {
 		rb.Add(nil, server.name, ERR_CHANOPRIVSNEEDED, client.Nick(), oldName, client.t("You're not a channel operator"))
 		return false
@@ -2441,14 +2442,14 @@ func renameHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *Re
 
 	founder := channel.Founder()
 	if founder != "" && founder != client.Account() {
-		rb.Add(nil, server.name, ERR_CANNOTRENAME, client.Nick(), oldName, newName, client.t("Only channel founders can change registered channels"))
+		rb.Add(nil, server.name, "FAIL", "RENAME", "CANNOT_RENAME", oldName, utils.SafeErrorParam(newName), client.t("Only channel founders can change registered channels"))
 		return false
 	}
 
 	config := server.Config()
 	status, _ := channel.historyStatus(config)
 	if status == HistoryPersistent {
-		rb.Add(nil, server.name, ERR_CANNOTRENAME, client.Nick(), oldName, newName, client.t("Channels with persistent history cannot be renamed"))
+		rb.Add(nil, server.name, "FAIL", "RENAME", "CANNOT_RENAME", oldName, utils.SafeErrorParam(newName), client.t("Channels with persistent history cannot be renamed"))
 		return false
 	}
 
@@ -2457,9 +2458,9 @@ func renameHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *Re
 	if err == errInvalidChannelName {
 		rb.Add(nil, server.name, ERR_NOSUCHCHANNEL, client.Nick(), utils.SafeErrorParam(newName), client.t(err.Error()))
 	} else if err == errChannelNameInUse {
-		rb.Add(nil, server.name, ERR_CHANNAMEINUSE, client.Nick(), utils.SafeErrorParam(newName), client.t(err.Error()))
+		rb.Add(nil, server.name, "FAIL", "RENAME", "CHANNEL_NAME_IN_USE", oldName, utils.SafeErrorParam(newName), client.t(err.Error()))
 	} else if err != nil {
-		rb.Add(nil, server.name, ERR_CANNOTRENAME, client.Nick(), oldName, utils.SafeErrorParam(newName), client.t("Cannot rename channel"))
+		rb.Add(nil, server.name, "FAIL", "RENAME", "CANNOT_RENAME", oldName, utils.SafeErrorParam(newName), client.t("Cannot rename channel"))
 	}
 	if err != nil {
 		return false

irc/numerics.go

@@ -168,8 +168,6 @@ const (
 	ERR_CANNOTSENDRP              = "573"
 	RPL_WHOISSECURE               = "671"
 	RPL_YOURLANGUAGESARE          = "687"
-	ERR_CHANNAMEINUSE             = "692"
-	ERR_CANNOTRENAME              = "693"
 	ERR_INVALIDMODEPARAM          = "696"
 	ERR_LISTMODEALREADYSET        = "697"
 	ERR_LISTMODENOTSET            = "698"