uvs: A stand-in for the yet-to-exist `uv shell` command

uvs

#!/usr/bin/env python3
#
# uvs: A stand-in for the yet-to-exist `uv shell` subcommand
#
# Copyright 2024 Rob Gilton
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in
#    the documentation and/or other materials provided with the
#    distribution.
# 3. Neither the name of the copyright holder nor the names of its
#    contributors may be used to endorse or promote products derived
#    from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.
from itertools import chain
from subprocess import run
from tempfile import NamedTemporaryFile
from pathlib import Path
import os
import sys
from typing import NoReturn


def require(condition: bool, error_msg: str) -> None:
    "Require that condition is true, otherwise exit with the given message"
    if not condition:
        print("Error:", error_msg, file=sys.stderr)
        exit(1)


def find_venv(root: Path) -> Path | None:
    "Find the closest virtualenv"
    root = root.absolute()

    for parent in chain([root], root.parents):
        venv = parent / ".venv"
        if venv.exists():
            return venv


def pretty_path(path: Path) -> Path:
    "Get a pretty, relative path to the given path from the working directory"
    return path.relative_to(Path.cwd(), walk_up=True)


shell = Path(os.environ["SHELL"])
require(shell.name == "bash", "This script only currently supports the bash shell")
require("VIRTUAL_ENV" not in os.environ, "Already within virtualenv")

venv = find_venv(Path.cwd())
require(venv is not None, "No venv found")

activate = venv / "bin" / "activate"
require(activate.exists(), f"Virtualenv at {venv} missing activate script")

env_file = venv.parent / ".env"
rc_lines = ["source $HOME/.bashrc", f"source {activate}"]
if env_file.exists():
    print(f"Using environment from {pretty_path(env_file)}")
    rc_lines += ["set -a", f"source {env_file}", "set +a"]

with NamedTemporaryFile("w", delete_on_close=False) as rc:
    rc.write("\n".join(rc_lines))
    rc.close()

    print(f"Entering virtualenv {pretty_path(venv)}")
    run(["bash", "--rcfile", rc.name])