Add an entry point for the completion tool

tools/completion/main.go

@@ -0,0 +1,84 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package completion
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/spf13/cobra"
+
+	"kitty/tools/cli"
+	"kitty/tools/utils"
+)
+
+func json_input_parser(data []byte, shell_state map[string]string) ([]string, error) {
+	ans := make([]string, 0, 32)
+	err := json.Unmarshal(data, &ans)
+	return ans, err
+}
+
+func json_output_serializer(completions *Completions, shell_state map[string]string) ([]byte, error) {
+	return json.Marshal(completions)
+}
+
+type parser_func func(data []byte, shell_state map[string]string) ([]string, error)
+type serializer_func func(completions *Completions, shell_state map[string]string) ([]byte, error)
+
+var input_parsers = make(map[string]parser_func, 4)
+var output_serializers = make(map[string]serializer_func, 4)
+
+func init() {
+	input_parsers["json"] = json_input_parser
+	output_serializers["json"] = json_output_serializer
+}
+
+func main(args []string) error {
+	output_type := "json"
+	if len(args) > 0 {
+		output_type = args[0]
+		args = args[1:]
+	}
+	shell_state := make(map[string]string, len(args))
+	for _, arg := range args {
+		k, v, found := utils.Cut(arg, "=")
+		if !found {
+			return fmt.Errorf("Invalid shell state specification: %s", arg)
+		}
+		shell_state[k] = v
+	}
+	input_parser := input_parsers[output_type]
+	output_serializer := output_serializers[output_type]
+	if input_parser == nil || output_serializer == nil {
+		return fmt.Errorf("Unknown output type: %s", output_type)
+	}
+	data, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		return err
+	}
+	argv, err := input_parser(data, shell_state)
+	if err != nil {
+		return err
+	}
+	completions := GetCompletions(argv)
+	output, err := output_serializer(completions, shell_state)
+	if err == nil {
+		os.Stdout.Write(output)
+	}
+	return err
+}
+
+func EntryPoint(tool_root *cobra.Command) *cobra.Command {
+	complete_command := cli.CreateCommand(&cobra.Command{
+		Use:    "__complete__ output_type [shell state...]",
+		Short:  "Generate completions for kitty commands",
+		Long:   "Generate completion candidates for kitty commands. The command line is read from STDIN. output_type can be one of the supported  shells or 'json' for JSON output.",
+		Hidden: true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return main(args)
+		},
+	})
+	return complete_command
+}