复制 DerivedData 根本没用：用 worktree 池让 Xcode 告别冷编译

以前：每个任务一个新目录
任务 1 ──> 新建 myapp.feat-A ──> 冷编译（82s） ──> 删除
任务 2 ──> 新建 myapp.feat-B ──> 冷编译（82s） ──> 删除

现在：目录固定
myapp.slot-0 ──> 切到 feat-A ──> 增量编译（26s） ──> 交还 ──> 切到 feat-B ──> 增量编译

#!/usr/bin/env python3
"""worktree 池：固定几个 worktree，换任务时在原目录里换分支。

  python3 slot.py acquire <分支>   认领一个空闲 slot 并切到该分支，打印路径
  python3 slot.py release <路径>   改动已推送后交还 slot
  python3 slot.py status           列出每个 slot 的状态

slot 是否空闲只看 git 状态：detached HEAD 且工作区干净。
"""

import argparse
import os
import subprocess
import sys
from pathlib import Path

SLOTS = int(os.environ.get("SLOT_COUNT", "3"))
BASE = os.environ.get("SLOT_BASE", "origin/main")


class SlotError(Exception):
    pass


def git(cwd, *args, check=True):
    r = subprocess.run(["git", *args], cwd=cwd, capture_output=True, text=True)
    if check and r.returncode != 0:
        raise SlotError(f"git {' '.join(args)} 失败：{(r.stderr or r.stdout).strip()}")
    return r


def main_root(cwd):
    # 从任何一个 slot 里调用，都能找到主 checkout
    common = git(cwd, "rev-parse", "--path-format=absolute", "--git-common-dir").stdout.strip()
    return Path(common).parent


def slot_paths(root):
    return [root.parent / f"{root.name}.slot-{i}" for i in range(SLOTS)]


def branch_of(path):
    return git(path, "symbolic-ref", "-q", "--short", "HEAD", check=False).stdout.strip() or None


def dirty(path):
    return bool(git(path, "status", "--porcelain").stdout.strip())


def pushed(path):
    return bool(git(path, "branch", "-r", "--contains", "HEAD").stdout.strip())


def free(path):
    return branch_of(path) is None and not dirty(path)


def acquire(root, branch):
    if f"branch refs/heads/{branch}" in git(root, "worktree", "list", "--porcelain").stdout:
        raise SlotError(f"分支 {branch} 已经在别的 worktree 里检出")
    git(root, "fetch", "--quiet", "origin")
    if git(root, "show-ref", "--verify", "-q", f"refs/heads/{branch}", check=False).returncode == 0:
        switch = ["switch", branch]
    elif git(root, "show-ref", "--verify", "-q", f"refs/remotes/origin/{branch}", check=False).returncode == 0:
        switch = ["switch", "-c", branch, "--track", f"origin/{branch}"]
    else:
        switch = ["switch", "-c", branch, "--no-track", BASE]
    for path in slot_paths(root):
        if not path.exists():
            git(root, "worktree", "add", "--detach", str(path), BASE)
        if not free(path):
            continue
        r = git(path, *switch, check=False)
        if r.returncode == 0:
            return path
        # 两个人同时抢同一个 slot 时，git 的 index.lock 只让一方成功，换下一个
        if "index.lock" not in r.stderr:
            raise SlotError(r.stderr.strip())
    raise SlotError("没有空闲 slot")


def release(root, path, force):
    path = path.resolve()
    if path not in [p.resolve() for p in slot_paths(root)]:
        raise SlotError(f"{path} 不是 slot")
    if dirty(path):
        raise SlotError("有未提交的改动，先提交推送，或确认丢弃")
    if not force and not pushed(path):
        raise SlotError("HEAD 还没推送到远端；确认不需要了再加 --force")
    branch = branch_of(path)
    git(root, "fetch", "--quiet", "origin")
    git(path, "switch", "--quiet", "--detach", BASE)
    if branch:
        # 代码已经在远端，删掉本地分支，下次从远端取最新的
        git(root, "branch", "-D", branch)


def status(root):
    for path in slot_paths(root):
        if not path.exists():
            print(f"{path.name}  未创建")
            continue
        state = "空闲" if free(path) else (branch_of(path) or "detached")
        note = "  有未提交改动" if dirty(path) else ""
        print(f"{path.name}  {state}{note}")


def main():
    p = argparse.ArgumentParser()
    sub = p.add_subparsers(dest="cmd", required=True)
    sub.add_parser("acquire").add_argument("branch")
    r = sub.add_parser("release")
    r.add_argument("path", type=Path)
    r.add_argument("--force", action="store_true")
    sub.add_parser("status")
    args = p.parse_args()
    try:
        root = main_root(Path.cwd())
        if args.cmd == "acquire":
            print(acquire(root, args.branch))
        elif args.cmd == "release":
            release(root, args.path, args.force)
        else:
            status(root)
    except SlotError as e:
        print(f"slot：{e}", file=sys.stderr)
        sys.exit(1)


if __name__ == "__main__":
    main()