Completion: Delegate kitty +complete to kitten

Implement `kitten __complete__ setup` in Go.
Fix zsh completion script to check `kitten`.

tools/cli/fish.go

@@ -12,12 +12,53 @@ import (
 
 var _ = fmt.Print
 
+func fish_completion_script(commands []string) ([]byte, error) {
+	// One command in fish requires one completion script.
+	// Usage: kitten __complete__ setup fish [kitty|kitten|clone-in-kitty]
+	all_commands := map[string]bool{
+		"kitty":          true,
+		"clone-in-kitty": true,
+		"kitten":         true,
+	}
+	if len(commands) == 0 {
+		for cmd, _ := range all_commands {
+			commands = append(commands, cmd)
+		}
+	}
+	script := strings.Builder{}
+	script.WriteString(`function __ksi_completions
+    set --local ct (commandline --current-token)
+    set --local tokens (commandline --tokenize --cut-at-cursor --current-process)
+    printf "%s\n" $tokens $ct | command kitten __complete__ fish | source -
+end
+
+`)
+	for _, cmd := range commands {
+		if all_commands[cmd] {
+			fmt.Fprintf(&script, "complete -f -c %s -a \"(__ksi_completions)\"\n", cmd)
+		} else if strings.Contains(cmd, "=") {
+			// Reserved for `setup SHELL [KEY=VALUE ...]`, not used now.
+			continue
+		} else {
+			return nil, fmt.Errorf("No fish completion script for command: %s", cmd)
+		}
+	}
+	return []byte(script.String()), nil
+}
+
 func fish_output_serializer(completions []*Completions, shell_state map[string]string) ([]byte, error) {
 	output := strings.Builder{}
 	f := func(format string, args ...any) { fmt.Fprintf(&output, format+"\n", args...) }
 	n := completions[0].Delegate.NumToRemove
 	fm := markup.New(false) // fish freaks out if there are escape codes in the description strings
-	if n > 0 {
+	legacy_completion := shell_state["_legacy_completion"]
+	if legacy_completion == "fish2" {
+		for _, mg := range completions[0].Groups {
+			for _, m := range mg.Matches {
+				f("%s", strings.ReplaceAll(m.Word+"\t"+fm.Prettify(m.Description), "\n", " "))
+			}
+		}
+	} else if n > 0 {
 		words := make([]string, len(completions[0].AllWords)-n+1)
 		words[0] = completions[0].Delegate.Command
 		copy(words[1:], completions[0].AllWords[n:])
@@ -40,6 +81,7 @@ func fish_output_serializer(completions []*Completions, shell_state map[string]s
 }
 
 func init() {
+	completion_scripts["fish"] = fish_completion_script
 	input_parsers["fish"] = shell_input_parser
 	output_serializers["fish"] = fish_output_serializer
 }