build/python/create_c_extension_import_hook.py

#!/usr/bin/env fuchsia-vendored-python
"""Creates a Python library for a C extension."""

# Copyright 2023 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import argparse
import os
import sys


def main():
    """Creates library wrapper"""

    parser = argparse.ArgumentParser(
        "Creates a Python library wrapper for a C extension."
    )
    parser.add_argument(
        "--target_name",
        help="Name of the build target",
        required=True,
    )
    parser.add_argument(
        "--shlib_source",
        help="Path to the shared library",
        required=True,
    )
    parser.add_argument(
        "--gen_dir",
        help="Path to gen directory, used to stage temp directories",
        required=True,
    )
    parser.add_argument("--output", help="Path to output", required=True)
    parser.add_argument(
        "--depfile",
        help="Path to the depfile to generate",
        type=argparse.FileType("w"),
        required=True,
    )

    args = parser.parse_args()
    app_dir = os.path.join(args.gen_dir, args.target_name)
    os.makedirs(app_dir, exist_ok=True)
    main_file = os.path.join(app_dir, "__init__.py")
    shlib_source_dir = os.path.dirname(args.shlib_source)
    if not shlib_source_dir:
        shlib_source_dir = os.path.join(".")
    shlib_source = os.path.basename(args.shlib_source)

    # Making this a list in the event that there are more deps.
    deps = " ".join([f"{args.shlib_source}.so"])
    args.depfile.write(f"{args.output}: {deps}\n")
    with open(main_file, "w", encoding="utf-8") as main_file_out:
        main_file_out.write(
            f"""
from importlib.abc import Loader
import importlib.util
import importlib.machinery
import os

def _init() -> object:
    finder = importlib.machinery.PathFinder()
    spec = finder.find_spec('{shlib_source}', path=['{shlib_source_dir}', os.getcwd()])
    if spec is None:
        raise Exception('Couldn\\'t load library "{shlib_source}" from {shlib_source_dir} or CWD"')
    mod = importlib.util.module_from_spec(spec)
    assert isinstance(spec.loader, Loader)
    spec.loader.exec_module(mod)
    return mod

__all__ = list(_init().__dict__.keys())
"""
        )
    return 0


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