simple implementation about generating i3wm config with include directive, [upstream](https://gitlab.com/haoliang-terraform/squidward/-/blob/master/i3/.config/i3/gencfg)

i3config.py

#!/usr/bin/env python3

import logging
import re
import shutil
import subprocess
from argparse import ArgumentParser, RawDescriptionHelpFormatter
from os import fdopen, unlink
from pathlib import Path
from tempfile import mkstemp


class Interpreter:
    pattern = re.compile(r"^(?P<indent>\s*)include\s+(?P<include>.+)\s+$")

    def __init__(self, mainfile: Path):
        self.mainfile = mainfile
        self.lookupdir = self.mainfile.parent

    @classmethod
    def from_fname(cls, fname: str):
        file = Path(fname)
        assert file.is_file()

        return cls(file.resolve())

    def __iter__(self):
        return self._interpret(self.mainfile)

    def _interpret(self, file: Path):
        """
        :raise: FileNotFound, PermissionError
        """

        # we assume config file should be small, lets say <= 32kb
        with file.open("rt") as fp:
            lines = fp.readlines()

        pattern = self.pattern

        for line in lines:
            matched = pattern.match(line)
            # support glob file name?
            if matched:
                indent = matched.group("indent")
                include = matched.group("include")
                yield from self._include(indent, include)
            else:
                yield line

    def _include(self, indent: str, fname: str):
        if "*" in fname:
            raise RuntimeError("include glob is not supported yet!")

        file = Path(fname)

        if not file.is_absolute():
            file = self.lookupdir.joinpath(file)

        logging.info("including file: %s", file)

        for line in self._interpret(file):
            if line == "\n":
                yield line
            else:
                yield indent + line


def _parse_args():
    desc = """
implements `include` directive in i3 config file
* if included-file is relative path, root will be argument main's parent

this script assumes following layout as default:

parts/
    * main
    * binding, ... whatever
    * local # will be ignored in git repo
    """

    parser = ArgumentParser(description=desc, formatter_class=RawDescriptionHelpFormatter)

    home = Path.home()
    default_main = home.joinpath(".config", "i3", "parts", "main")
    parser.add_argument("main", type=str, nargs="?", default=default_main)
    default_out = home.joinpath(".config", "i3", "config")
    parser.add_argument("out", type=str, nargs="?", default=default_out)

    parser.add_argument("--no-backup", action="store_true")

    return parser.parse_args()


def main():
    args = _parse_args()

    mainfile = args.main
    outfile = Path(args.out).resolve()

    if not args.no_backup:
        bakfile = outfile.parent.joinpath(outfile.name + ".bak")

    tempfd, tempfname = mkstemp("wt")

    try:
        logging.info("stores in tempfile: %s", tempfname)
        with fdopen(tempfd, "wt") as tempfp:
            for line in Interpreter.from_fname(mainfile):
                tempfp.write(line)

        logging.info("checking final i3 config file validity")
        subprocess.run(["i3", "-c", tempfname, "-C", "-V"], check=True)

        if not args.no_backup:
            logging.info("create backup %s", bakfile)
            try:
                shutil.move(outfile, bakfile)
            except FileNotFoundError:
                logging.warning("outfile not exist, no backup")

        logging.info("moving tempfile to %s", outfile)
        shutil.move(tempfname, outfile)
    finally:
        logging.info("deleting tempfile")
        try:
            unlink(tempfname)
        except FileNotFoundError:
            pass


if __name__ == "__main__":
    logging.basicConfig(
        level="DEBUG",
        style="{",
        datefmt="%Y-%m-%d %H:%M:%S",
        format="{asctime} {message}",
    )

    main()

i3wm has implemented the include directive in here, and this feature will be shipped in 4.20