python/private/python_bootstrap_template.txt

%shebang%
# vim: syntax=python

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import sys

import os
import subprocess
import uuid

# runfiles-relative path
STAGE2_BOOTSTRAP="%stage2_bootstrap%"

# runfiles-relative path to venv's python interpreter
# Empty string if a venv is not setup.
PYTHON_BINARY = '%python_binary%'

# The path to the actual interpreter that is used.
# Typically PYTHON_BINARY is a symlink pointing to this.
# runfiles-relative path, absolute path, or single word.
# Used to create a venv at runtime, or when a venv isn't setup.
PYTHON_BINARY_ACTUAL = "%python_binary_actual%"

# 0 or 1.
# 1 if this bootstrap was created for placement within a zipfile. 0 otherwise.
IS_ZIPFILE = "%is_zipfile%" == "1"
# 0 or 1.
# If 1, then a venv will be created at runtime that replicates what would have
# been the build-time structure.
RECREATE_VENV_AT_RUNTIME="%recreate_venv_at_runtime%"

WORKSPACE_NAME = "%workspace_name%"

# Target-specific interpreter args.
INTERPRETER_ARGS = [
%interpreter_args%
]

ADDITIONAL_INTERPRETER_ARGS = os.environ.get("RULES_PYTHON_ADDITIONAL_INTERPRETER_ARGS", "")

def IsRunningFromZip():
  return IS_ZIPFILE

if IsRunningFromZip():
  import shutil
  import tempfile
  import zipfile
else:
  import re

# Return True if running on Windows
def IsWindows():
  return os.name == 'nt'

def GetWindowsPathWithUNCPrefix(path):
  """Adds UNC prefix after getting a normalized absolute Windows path.

  No-op for non-Windows platforms or if running under python2.
  """
  path = path.strip()

  # No need to add prefix for non-Windows platforms.
  # And \\?\ doesn't work in python 2 or on mingw
  if not IsWindows() or sys.version_info[0] < 3:
    return path

  # Starting in Windows 10, version 1607(OS build 14393), MAX_PATH limitations have been
  # removed from common Win32 file and directory functions.
  # Related doc: https://docs.microsoft.com/en-us/windows/win32/fileio/maximum-file-path-limitation?tabs=cmd#enable-long-paths-in-windows-10-version-1607-and-later
  import platform
  win32_version = None
  # Windows 2022 with Python 3.12.8 gives flakey errors, so try a couple times.
  for _ in range(3):
    try:
      win32_version = platform.win32_ver()[1]
      break
    except (ValueError, KeyError):
      pass
  if win32_version and win32_version >= '10.0.14393':
    return path

  # import sysconfig only now to maintain python 2.6 compatibility
  import sysconfig
  if sysconfig.get_platform() == 'mingw':
    return path

  # Lets start the unicode fun
  unicode_prefix = '\\\\?\\'
  if path.startswith(unicode_prefix):
    return path

  # os.path.abspath returns a normalized absolute path
  return unicode_prefix + os.path.abspath(path)

def HasWindowsExecutableExtension(path):
  return path.endswith('.exe') or path.endswith('.com') or path.endswith('.bat')

if PYTHON_BINARY and IsWindows() and not HasWindowsExecutableExtension(PYTHON_BINARY):
  PYTHON_BINARY = PYTHON_BINARY + '.exe'

def SearchPath(name):
  """Finds a file in a given search path."""
  search_path = os.getenv('PATH', os.defpath).split(os.pathsep)
  for directory in search_path:
    if directory:
      path = os.path.join(directory, name)
      if os.path.isfile(path) and os.access(path, os.X_OK):
        return path
  return None

def FindPythonBinary(module_space):
  """Finds the real Python binary if it's not a normal absolute path."""
  if PYTHON_BINARY:
    return FindBinary(module_space, PYTHON_BINARY)
  else:
    return FindBinary(module_space, PYTHON_BINARY_ACTUAL)


def print_verbose(*args, mapping=None, values=None):
    if os.environ.get("RULES_PYTHON_BOOTSTRAP_VERBOSE"):
        if mapping is not None:
            for key, value in sorted((mapping or {}).items()):
                print(
                    "bootstrap: stage 1: ",
                    *(list(args) + ["{}={}".format(key, repr(value))]),
                    file=sys.stderr,
                    flush=True
                )
        elif values is not None:
            for i, v in enumerate(values):
                print(
                    "bootstrap: stage 1:",
                    *(list(args) + ["[{}] {}".format(i, repr(v))]),
                    file=sys.stderr,
                    flush=True
                )
        else:
            print("bootstrap: stage 1:", *args, file=sys.stderr, flush=True)

def FindBinary(module_space, bin_name):
  """Finds the real binary if it's not a normal absolute path."""
  if not bin_name:
    return None
  if bin_name.startswith("//"):
    # Case 1: Path is a label. Not supported yet.
    raise AssertionError(
        "Bazel does not support execution of Python interpreters via labels yet"
    )
  elif os.path.isabs(bin_name):
    # Case 2: Absolute path.
    return bin_name
  # Use normpath() to convert slashes to os.sep on Windows.
  elif os.sep in os.path.normpath(bin_name):
    # Case 3: Path is relative to the repo root.
    return os.path.join(module_space, bin_name)
  else:
    # Case 4: Path has to be looked up in the search path.
    return SearchPath(bin_name)

def FindModuleSpace(main_rel_path):
  """Finds the runfiles tree."""
  # When the calling process used the runfiles manifest to resolve the
  # location of this stub script, the path may be expanded. This means
  # argv[0] may no longer point to a location inside the runfiles
  # directory. We should therefore respect RUNFILES_DIR and
  # RUNFILES_MANIFEST_FILE set by the caller.
  runfiles_dir = os.environ.get('RUNFILES_DIR', None)
  if not runfiles_dir:
    runfiles_manifest_file = os.environ.get('RUNFILES_MANIFEST_FILE', '')
    if (runfiles_manifest_file.endswith('.runfiles_manifest') or
        runfiles_manifest_file.endswith('.runfiles/MANIFEST')):
      runfiles_dir = runfiles_manifest_file[:-9]
  # Be defensive: the runfiles dir should contain our main entry point. If
  # it doesn't, then it must not be our runfiles directory.
  if runfiles_dir and os.path.exists(os.path.join(runfiles_dir, main_rel_path)):
    return runfiles_dir

  stub_filename = sys.argv[0]
  # On Windows, the path may contain both forward and backslashes.
  # Normalize to the OS separator because the regex used later assumes
  # the OS-specific separator.
  if IsWindows:
    stub_filename = stub_filename.replace("/", os.sep)

  if not os.path.isabs(stub_filename):
    stub_filename = os.path.join(os.getcwd(), stub_filename)

  while True:
    module_space = stub_filename + ('.exe' if IsWindows() else '') + '.runfiles'
    if os.path.isdir(module_space):
      return module_space

    runfiles_pattern = r'(.*\.runfiles)' + (r'\\' if IsWindows() else '/') + '.*'
    matchobj = re.match(runfiles_pattern, stub_filename)
    if matchobj:
      return matchobj.group(1)

    if not os.path.islink(stub_filename):
      break
    target = os.readlink(stub_filename)
    if os.path.isabs(target):
      stub_filename = target
    else:
      stub_filename = os.path.join(os.path.dirname(stub_filename), target)

  raise AssertionError('Cannot find .runfiles directory for %s' % sys.argv[0])

def ExtractZip(zip_path, dest_dir):
  """Extracts the contents of a zip file, preserving the unix file mode bits.

  These include the permission bits, and in particular, the executable bit.

  Ideally the zipfile module should set these bits, but it doesn't. See:
  https://bugs.python.org/issue15795.

  Args:
      zip_path: The path to the zip file to extract
      dest_dir: The path to the destination directory
  """
  zip_path = GetWindowsPathWithUNCPrefix(zip_path)
  dest_dir = GetWindowsPathWithUNCPrefix(dest_dir)
  with zipfile.ZipFile(zip_path) as zf:
    for info in zf.infolist():
      zf.extract(info, dest_dir)
      # UNC-prefixed paths must be absolute/normalized. See
      # https://docs.microsoft.com/en-us/windows/desktop/fileio/naming-a-file#maximum-path-length-limitation
      file_path = os.path.abspath(os.path.join(dest_dir, info.filename))
      # The Unix st_mode bits (see "man 7 inode") are stored in the upper 16
      # bits of external_attr. Of those, we set the lower 12 bits, which are the
      # file mode bits (since the file type bits can't be set by chmod anyway).
      attrs = info.external_attr >> 16
      if attrs != 0:  # Rumor has it these can be 0 for zips created on Windows.
        os.chmod(file_path, attrs & 0o7777)

# Create the runfiles tree by extracting the zip file
def CreateModuleSpace():
  temp_dir = tempfile.mkdtemp('', 'Bazel.runfiles_')
  ExtractZip(os.path.dirname(__file__), temp_dir)
  # IMPORTANT: Later code does `rm -fr` on dirname(module_space) -- it's
  # important that deletion code be in sync with this directory structure
  return os.path.join(temp_dir, 'runfiles')

def RunfilesEnvvar(module_space):
  """Finds the runfiles manifest or the runfiles directory.

  Returns:
    A tuple of (var_name, var_value) where var_name is either 'RUNFILES_DIR' or
    'RUNFILES_MANIFEST_FILE' and var_value is the path to that directory or
    file, or (None, None) if runfiles couldn't be found.
  """
  # If this binary is the data-dependency of another one, the other sets
  # RUNFILES_MANIFEST_FILE or RUNFILES_DIR for our sake.
  runfiles = os.environ.get('RUNFILES_MANIFEST_FILE', None)
  if runfiles:
    return ('RUNFILES_MANIFEST_FILE', runfiles)

  runfiles = os.environ.get('RUNFILES_DIR', None)
  if runfiles:
    return ('RUNFILES_DIR', runfiles)

  # If running from a zip, there's no manifest file.
  if IsRunningFromZip():
    return ('RUNFILES_DIR', module_space)

  # Look for the runfiles "output" manifest, argv[0] + ".runfiles_manifest"
  runfiles = module_space + '_manifest'
  if os.path.exists(runfiles):
    return ('RUNFILES_MANIFEST_FILE', runfiles)

  # Look for the runfiles "input" manifest, argv[0] + ".runfiles/MANIFEST"
  # Normally .runfiles_manifest and MANIFEST are both present, but the
  # former will be missing for zip-based builds or if someone copies the
  # runfiles tree elsewhere.
  runfiles = os.path.join(module_space, 'MANIFEST')
  if os.path.exists(runfiles):
    return ('RUNFILES_MANIFEST_FILE', runfiles)

  # If running in a sandbox and no environment variables are set, then
  # Look for the runfiles  next to the binary.
  if module_space.endswith('.runfiles') and os.path.isdir(module_space):
    return ('RUNFILES_DIR', module_space)

  return (None, None)

def ExecuteFile(python_program, main_filename, args, env, module_space,
                workspace, delete_module_space):
  # type: (str, str, list[str], dict[str, str], str, str|None, str|None) -> ...
  """Executes the given Python file using the various environment settings.

  This will not return, and acts much like os.execv, except is much
  more restricted, and handles Bazel-related edge cases.

  Args:
    python_program: (str) Path to the Python binary to use for execution
    main_filename: (str) The Python file to execute
    args: (list[str]) Additional args to pass to the Python file
    env: (dict[str, str]) A dict of environment variables to set for the execution
    module_space: (str) Path to the module space/runfiles tree directory
    workspace: (str|None) Name of the workspace to execute in. This is expected to be a
        directory under the runfiles tree.
    delete_module_space: (bool), True if the module space should be deleted
        after a successful (exit code zero) program run, False if not.
  """
  argv = [python_program]
  argv.extend(INTERPRETER_ARGS)
  additional_interpreter_args = os.environ.pop("RULES_PYTHON_ADDITIONAL_INTERPRETER_ARGS", "")
  if additional_interpreter_args:
    import shlex
    argv.extend(shlex.split(additional_interpreter_args))
  argv.append(main_filename)
  argv.extend(args)
  # We want to use os.execv instead of subprocess.call, which causes
  # problems with signal passing (making it difficult to kill
  # Bazel). However, these conditions force us to run via
  # subprocess.call instead:
  #
  # - On Windows, os.execv doesn't handle arguments with spaces
  #   correctly, and it actually starts a subprocess just like
  #   subprocess.call.
  # - When running in a workspace or zip file, we need to clean up the
  #   workspace after the process finishes so control must return here.
  # - If we may need to emit a host config warning after execution, we
  #   can't execv because we need control to return here. This only
  #   happens for targets built in the host config.
  #
  if not (IsWindows() or workspace or delete_module_space):
    _RunExecv(python_program, argv, env)

  ret_code = subprocess.call(
    argv,
    env=env,
    cwd=workspace
  )

  if delete_module_space:
    # NOTE: dirname() is called because CreateModuleSpace() creates a
    # sub-directory within a temporary directory, and we want to remove the
    # whole temporary directory.
    shutil.rmtree(os.path.dirname(module_space), True)
  sys.exit(ret_code)

def _RunExecv(python_program, argv, env):
  # type: (str, list[str], dict[str, str]) -> ...
  """Executes the given Python file using the various environment settings."""
  os.environ.update(env)
  print_verbose("RunExecv: environ:", mapping=os.environ)
  print_verbose("RunExecv: python:", python_program)
  print_verbose("RunExecv: argv:", values=argv)
  os.execv(python_program, argv)

def Main():
  print_verbose("initial argv:", values=sys.argv)
  print_verbose("initial cwd:", os.getcwd())
  print_verbose("initial environ:", mapping=os.environ)
  print_verbose("initial sys.path:", values=sys.path)
  args = sys.argv[1:]

  new_env = {}

  # NOTE: We call normpath for two reasons:
  # 1. Transform Bazel `foo/bar` to Windows `foo\bar`
  # 2. Transform `_main/../foo/main.py` to simply `foo/main.py`, which
  #    matters if `_main` doesn't exist (which can occur if a binary
  #    is packaged and needs no artifacts from the main repo)
  main_rel_path = os.path.normpath(STAGE2_BOOTSTRAP)

  if IsRunningFromZip():
    module_space = CreateModuleSpace()
    delete_module_space = True
  else:
    module_space = FindModuleSpace(main_rel_path)
    delete_module_space = False

  if os.environ.get("RULES_PYTHON_TESTING_TELL_MODULE_SPACE"):
    new_env["RULES_PYTHON_TESTING_MODULE_SPACE"] = module_space

  runfiles_envkey, runfiles_envvalue = RunfilesEnvvar(module_space)
  if runfiles_envkey:
    new_env[runfiles_envkey] = runfiles_envvalue

  # Don't prepend a potentially unsafe path to sys.path
  # See: https://docs.python.org/3.11/using/cmdline.html#envvar-PYTHONSAFEPATH
  new_env['PYTHONSAFEPATH'] = '1'

  main_filename = os.path.join(module_space, main_rel_path)
  main_filename = GetWindowsPathWithUNCPrefix(main_filename)
  assert os.path.exists(main_filename), \
         'Cannot exec() %r: file not found.' % main_filename
  assert os.access(main_filename, os.R_OK), \
         'Cannot exec() %r: file not readable.' % main_filename

  program = python_program = FindPythonBinary(module_space)
  if python_program is None:
    raise AssertionError('Could not find python binary: ' + repr(PYTHON_BINARY))

  # Some older Python versions on macOS (namely Python 3.7) may unintentionally
  # leave this environment variable set after starting the interpreter, which
  # causes problems with Python subprocesses correctly locating sys.executable,
  # which subsequently causes failure to launch on Python 3.11 and later.
  if '__PYVENV_LAUNCHER__' in os.environ:
    del os.environ['__PYVENV_LAUNCHER__']

  new_env.update((key, val) for key, val in os.environ.items() if key not in new_env)

  workspace = None
  if IsRunningFromZip():
    # If RUN_UNDER_RUNFILES equals 1, it means we need to
    # change directory to the right runfiles directory.
    # (So that the data files are accessible)
    if os.environ.get('RUN_UNDER_RUNFILES') == '1':
      workspace = os.path.join(module_space, WORKSPACE_NAME)

  try:
    sys.stdout.flush()
    # NOTE: ExecuteFile may call execve() and lines after this will never run.
    ExecuteFile(
      python_program, main_filename, args, new_env, module_space,
      workspace,
      delete_module_space = delete_module_space,
    )

  except EnvironmentError:
    # This works from Python 2.4 all the way to 3.x.
    e = sys.exc_info()[1]
    # This exception occurs when os.execv() fails for some reason.
    if not getattr(e, 'filename', None):
      e.filename = program  # Add info to error message
    raise

if __name__ == '__main__':
  Main()