bazelisk.py

#!/usr/bin/env python3
"""
Copyright 2018 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""

from contextlib import closing
from distutils.version import LooseVersion
import json
import os
import os.path
import platform
import re
import shutil
import subprocess
import sys
import tempfile
import time

try:
    from urllib.request import urlopen
except ImportError:
    # Python 2.x compatibility hack.
    from urllib2 import urlopen

ONE_HOUR = 1 * 60 * 60

LATEST_PATTERN = re.compile(r"latest(-(?P<offset>\d+))?$")

LAST_GREEN_COMMIT_BASE_PATH = (
    "https://storage.googleapis.com/bazel-untrusted-builds/last_green_commit/"
)

LAST_GREEN_COMMIT_PATH_SUFFIXES = {
    "last_green": "github.com/bazelbuild/bazel.git/bazel-bazel",
    "last_downstream_green": "downstream_pipeline",
}

BAZEL_GCS_PATH_PATTERN = (
    "https://storage.googleapis.com/bazel-builds/artifacts/{platform}/{commit}/bazel"
)

SUPPORTED_PLATFORMS = {"linux": "ubuntu1404", "windows": "windows", "darwin": "macos"}

TOOLS_BAZEL_PATH = "./tools/bazel"

BAZEL_REAL = "BAZEL_REAL"


def decide_which_bazel_version_to_use():
    # Check in this order:
    # - env var "USE_BAZEL_VERSION" is set to a specific version.
    # - env var "USE_NIGHTLY_BAZEL" or "USE_BAZEL_NIGHTLY" is set -> latest
    #   nightly. (TODO)
    # - env var "USE_CANARY_BAZEL" or "USE_BAZEL_CANARY" is set -> latest
    #   rc. (TODO)
    # - the file workspace_root/tools/bazel exists -> that version. (TODO)
    # - workspace_root/.bazelversion exists -> read contents, that version.
    # - workspace_root/WORKSPACE contains a version -> that version. (TODO)
    # - fallback: latest release
    if "USE_BAZEL_VERSION" in os.environ:
        return os.environ["USE_BAZEL_VERSION"]

    workspace_root = find_workspace_root()
    if workspace_root:
        bazelversion_path = os.path.join(workspace_root, ".bazelversion")
        if os.path.exists(bazelversion_path):
            with open(bazelversion_path, "r") as f:
                return f.read().strip()

    return "latest"


def find_workspace_root(root=None):
    if root is None:
        root = os.getcwd()
    if os.path.exists(os.path.join(root, "WORKSPACE")):
        return root
    new_root = os.path.dirname(root)
    return find_workspace_root(new_root) if new_root != root else None


def resolve_version_label_to_number_or_commit(bazelisk_directory, version):
    """Resolves the given label to a released version of Bazel or a commit.

    Args:
        bazelisk_directory: string; path to a directory that can store
            temporary data for Bazelisk.
        version: string; the version label that should be resolved.
    Returns:
        A (string, bool) tuple that consists of two parts:
        1. the resolved number of a Bazel release (candidate), or the commit
            of an unreleased Bazel binary,
        2. An indicator for whether the returned version refers to a commit.
    """
    suffix = LAST_GREEN_COMMIT_PATH_SUFFIXES.get(version)
    if suffix:
        return get_last_green_commit(suffix), True

    if "latest" in version:
        match = LATEST_PATTERN.match(version)
        if not match:
            raise Exception(
                'Invalid version "{}". In addition to using a version '
                'number such as "0.20.0", you can use values such as '
                '"latest" and "latest-N", with N being a non-negative '
                "integer.".format(version)
            )

        history = get_version_history(bazelisk_directory)
        offset = int(match.group("offset") or "0")
        return resolve_latest_version(history, offset), False

    return version, False


def get_last_green_commit(path_suffix):
    return read_remote_text_file(LAST_GREEN_COMMIT_BASE_PATH + path_suffix).strip()


def get_releases_json(bazelisk_directory):
    """Returns the most recent versions of Bazel, in descending order."""
    releases = os.path.join(bazelisk_directory, "releases.json")

    # Use a cached version if it's fresh enough.
    if os.path.exists(releases):
        if abs(time.time() - os.path.getmtime(releases)) < ONE_HOUR:
            with open(releases, "rb") as f:
                try:
                    return json.loads(f.read().decode("utf-8"))
                except ValueError:
                    print("WARN: Could not parse cached releases.json.")
                    pass

    with open(releases, "wb") as f:
        body = read_remote_text_file("https://api.github.com/repos/bazelbuild/bazel/releases")
        f.write(body.encode("utf-8"))
        return json.loads(body)


def read_remote_text_file(url):
    with closing(urlopen(url)) as res:
        body = res.read()
        try:
            return body.decode(res.info().get_content_charset("iso-8859-1"))
        except AttributeError:
            # Python 2.x compatibility hack
            return body.decode(res.info().getparam("charset") or "iso-8859-1")


def get_version_history(bazelisk_directory):
    ordered = sorted(
        (
            LooseVersion(release["tag_name"])
            for release in get_releases_json(bazelisk_directory)
            if not release["prerelease"]
        ),
        reverse=True,
    )
    return [str(v) for v in ordered]


def resolve_latest_version(version_history, offset):
    if offset >= len(version_history):
        version = "latest-{}".format(offset) if offset else "latest"
        raise Exception(
            'Cannot resolve version "{}": There are only {} Bazel '
            "releases.".format(version, len(version_history))
        )

    # This only works since we store the history in descending order.
    return version_history[offset]


def get_operating_system():
    operating_system = platform.system().lower()
    if operating_system not in ("linux", "darwin", "windows"):
        raise Exception(
            'Unsupported operating system "{}". '
            "Bazel currently only supports Linux, macOS and Windows.".format(operating_system)
        )
    return operating_system


def determine_bazel_filename(version):
    machine = normalized_machine_arch_name()
    if machine != "x86_64":
        raise Exception(
            'Unsupported machine architecture "{}". Bazel currently only supports x86_64.'.format(
                machine
            )
        )

    operating_system = get_operating_system()

    filename_ending = ".exe" if operating_system == "windows" else ""
    return "bazel-{}-{}-{}{}".format(version, operating_system, machine, filename_ending)


def normalized_machine_arch_name():
    machine = platform.machine().lower()
    if machine == "amd64":
        machine = "x86_64"
    return machine


def determine_url(version, is_commit, bazel_filename):
    if is_commit:
        sys.stderr.write("Using unreleased version at commit {}\n".format(version))
        # No need to validate the platform thanks to determine_bazel_filename().
        return BAZEL_GCS_PATH_PATTERN.format(
            platform=SUPPORTED_PLATFORMS[platform.system().lower()], commit=version
        )

    # Split version into base version and optional additional identifier.
    # Example: '0.19.1' -> ('0.19.1', None), '0.20.0rc1' -> ('0.20.0', 'rc1')
    (version, rc) = re.match(r"(\d*\.\d*(?:\.\d*)?)(rc\d+)?", version).groups()
    return "https://releases.bazel.build/{}/{}/{}".format(
        version, rc if rc else "release", bazel_filename
    )


def download_bazel_into_directory(version, is_commit, directory):
    bazel_filename = determine_bazel_filename(version)
    url = determine_url(version, is_commit, bazel_filename)
    destination_path = os.path.join(directory, bazel_filename)
    if not os.path.exists(destination_path):
        sys.stderr.write("Downloading {}...\n".format(url))
        with tempfile.NamedTemporaryFile(prefix="bazelisk", dir=directory, delete=False) as t:
            with closing(urlopen(url)) as response:
                shutil.copyfileobj(response, t)
            t.flush()
            os.fsync(t.fileno())
        os.rename(t.name, destination_path)
    os.chmod(destination_path, 0o755)
    return destination_path


def get_bazelisk_directory():
    bazelisk_home = os.environ.get("BAZELISK_HOME")
    if bazelisk_home is not None:
        return bazelisk_home

    operating_system = get_operating_system()

    base_dir = None

    if operating_system == "windows":
        base_dir = os.environ.get("LocalAppData")
        if base_dir is None:
            raise Exception("%LocalAppData% is not defined")
    elif operating_system == "darwin":
        base_dir = os.environ.get("HOME")
        if base_dir is None:
            raise Exception("$HOME is not defined")
        base_dir = os.path.join(base_dir, "Library/Caches")
    elif operating_system == "linux":
        base_dir = os.environ.get("XDG_CACHE_HOME")
        if base_dir is None:
            base_dir = os.environ.get("HOME")
            if base_dir is None:
                raise Exception("neither $XDG_CACHE_HOME nor $HOME are defined")
            base_dir = os.path.join(base_dir, ".cache")
    else:
        raise Exception("Unsupported operating system '{}'".format(operating_system))

    return os.path.join(base_dir, "bazelisk")


def maybe_makedirs(path):
    """
  Creates a directory and its parents if necessary.
  """
    try:
        os.makedirs(path)
    except OSError as e:
        if not os.path.isdir(path):
            raise e


def delegate_tools_bazel(bazel_path):
    """Match Bazel's own delegation behavior in the builds distributed by most
    package managers: use tools/bazel if it's present, executable, and not this
    script.
    """
    root = find_workspace_root()
    if root:
        wrapper = os.path.join(root, TOOLS_BAZEL_PATH)
        if os.path.exists(wrapper) and os.access(wrapper, os.X_OK):
            try:
                if not os.path.samefile(wrapper, __file__):
                    return wrapper
            except AttributeError:
                # Python 2 on Windows does not support os.path.samefile
                if os.path.abspath(wrapper) != os.path.abspath(__file__):
                    return wrapper
    return None


def execute_bazel(bazel_path, argv):
    wrapper = delegate_tools_bazel(bazel_path)
    if wrapper:
        os.putenv(BAZEL_REAL, bazel_path)
        bazel_path = wrapper

    # We cannot use close_fds on Windows, so disable it there.
    p = subprocess.Popen([bazel_path] + argv, close_fds=os.name != "nt")
    while True:
        try:
            return p.wait()
        except KeyboardInterrupt:
            # Bazel will also get the signal and terminate.
            # We should continue waiting until it does so.
            pass


def main(argv=None):
    if argv is None:
        argv = sys.argv

    bazelisk_directory = get_bazelisk_directory()
    maybe_makedirs(bazelisk_directory)

    bazel_version = decide_which_bazel_version_to_use()
    bazel_version, is_commit = resolve_version_label_to_number_or_commit(
        bazelisk_directory, bazel_version
    )

    bazel_directory = os.path.join(bazelisk_directory, "bin")
    maybe_makedirs(bazel_directory)
    bazel_path = download_bazel_into_directory(bazel_version, is_commit, bazel_directory)

    return execute_bazel(bazel_path, argv[1:])


if __name__ == "__main__":
    sys.exit(main())