implement command aliases (#2236)

See #2229

default.yaml

@@ -375,6 +375,11 @@ server:
     # if you don't want to publicize how popular the server is
     suppress-lusers: false
 
+    # optionally map command alias names to existing ergo commands. most deployments
+    # should ignore this.
+    #command-aliases:
+        #"UMGEBUNG": "AMBIANCE"
+
 # account options
 accounts:
     # is account authentication enabled, i.e., can users log into existing accounts?

irc/client.go

@@ -750,13 +750,8 @@ func (client *Client) run(session *Session) {
 			break
 		}
 
-		cmd, exists := Commands[msg.Command]
-		if !exists {
-			cmd = unknownCommand
-		} else if invalidUtf8 {
-			cmd = invalidUtf8Command
-		}
-
+		var cmd Command
+		msg.Command, cmd = client.server.resolveCommand(msg.Command, invalidUtf8)
 		isExiting := cmd.Run(client.server, client, session, msg)
 		if isExiting {
 			break

irc/commands.go

@@ -18,6 +18,24 @@ type Command struct {
 	capabs         []string
 }
 
+// resolveCommand returns the command to execute in response to a user input line.
+// some invalid commands (unknown command verb, invalid UTF8) get a fake handler
+// to ensure that labeled-response still works as expected.
+func (server *Server) resolveCommand(command string, invalidUTF8 bool) (canonicalName string, result Command) {
+	if invalidUTF8 {
+		return command, invalidUtf8Command
+	}
+	if cmd, ok := Commands[command]; ok {
+		return command, cmd
+	}
+	if target, ok := server.Config().Server.CommandAliases[command]; ok {
+		if cmd, ok := Commands[target]; ok {
+			return target, cmd
+		}
+	}
+	return command, unknownCommand
+}
+
 // Run runs this command with the given client/message.
 func (cmd *Command) Run(server *Server, client *Client, session *Session, msg ircmsg.Message) (exiting bool) {
 	rb := NewResponseBuffer(session)

irc/config.go

@@ -609,6 +609,7 @@ type Config struct {
 		OverrideServicesHostname string              `yaml:"override-services-hostname"`
 		MaxLineLen               int                 `yaml:"max-line-len"`
 		SuppressLusers           bool                `yaml:"suppress-lusers"`
+		CommandAliases           map[string]string   `yaml:"command-aliases"`
 	}
 
 	API struct {
@@ -1660,6 +1661,11 @@ func LoadConfig(filename string) (config *Config, err error) {
 		return nil, err
 	}
 
+	config.Server.CommandAliases, err = normalizeCommandAliases(config.Server.CommandAliases)
+	if err != nil {
+		return nil, err
+	}
+
 	// now that all postprocessing is complete, regenerate ISUPPORT:
 	err = config.generateISupport()
 	if err != nil {
@@ -1875,3 +1881,22 @@ func (config *Config) loadMOTD() error {
 	}
 	return nil
 }
+
+func normalizeCommandAliases(aliases map[string]string) (normalizedAliases map[string]string, err error) {
+	if len(aliases) == 0 {
+		return nil, nil
+	}
+	normalizedAliases = make(map[string]string, len(aliases))
+	for alias, command := range aliases {
+		alias = strings.ToUpper(alias)
+		command = strings.ToUpper(command)
+		if _, found := Commands[alias]; found {
+			return nil, fmt.Errorf("Command alias `%s` collides with a real Ergo command", alias)
+		}
+		if _, found := Commands[command]; !found {
+			return nil, fmt.Errorf("Command alias `%s` mapped to non-existent Ergo command `%s`", alias, command)
+		}
+		normalizedAliases[alias] = command
+	}
+	return normalizedAliases, nil
+}

traditional.yaml

@@ -347,6 +347,11 @@ server:
     # if you don't want to publicize how popular the server is
     suppress-lusers: false
 
+    # optionally map command alias names to existing ergo commands. most deployments
+    # should ignore this.
+    #command-aliases:
+        #"UMGEBUNG": "AMBIANCE"
+
 # account options
 accounts:
     # is account authentication enabled, i.e., can users log into existing accounts?