which-header

#!/usr/bin/env python3
"""locate headers #included by the GCC C Preprocessor
SPDX-FileCopyrightText: 2024 Eli Array Minkoff

SPDX-License-Identifier: 0BSD
"""

import argparse
import subprocess
from pathlib import Path
import os

_CPP_INFO = subprocess.check_output(
    # https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html
    ["cpp", "-v", "/dev/null", "-o", "/dev/null"],
    stderr=subprocess.STDOUT,
).decode()

# cut off information after search list
_CPP_INFO = _CPP_INFO.split("End of search list.\n", 1)[0]

# cut off information before search list
_CPP_INFO = _CPP_INFO.split('#include "..." search starts here:\n', 1)[1]

_quoted, _default = _CPP_INFO.split("#include <...> search starts here:\n", 1)
# path names listed are indented with single spaces.
quoted_search_dirs = [Path.cwd()] + [Path(p[1:]) for p in _quoted.splitlines()]

default_search_dirs = [Path(p[1:]) for p in _default.splitlines()]


def _get_args() -> argparse.Namespace:
    """Parse the command-line flags, return a Namespace object"""
    parser = argparse.ArgumentParser(
        description="Locate header included by gcc's cpp",
        allow_abbrev=False,
    )
    # add basic arguments
    parser.add_argument(
        "--quoted",
        "-Q",
        action="store_true",
        dest="quoted",
        help="treat files as though they're included with quotes",
    )
    parser.add_argument(
        "-iquoted",
        action="append",
        dest="quoted_includes",
        type=Path,
        help="Extra directory for search path for quoted includes only",
    )
    parser.add_argument(
        "-I",
        "-include",
        "-isystem",
        "--include",
        action="append",
        dest="includes",
        type=Path,
        help="extra directory for search path",
    )
    parser.add_argument(
        "-a",
        "--all-matches",
        action="store_true",
        dest="all_matches",
        help="Print all matched headers, rather than the 1st",
    )

    parser.add_argument("headers", nargs="*", help="headers to look up")
    return parser.parse_args()


def find_header(
    header: str | os.PathLike,
    search_dirs: list[Path],
    return_all: bool = False,
) -> Path | list[Path]:
    """Return a pathlib.Path to the header
    parameters:
        header: the header to search for
        search_dirs: the directories in the search path

    if header can't be found, raises a FileNotFoundError.
    """
    ret = []
    for search_dir in search_dirs:
        if (joined := search_dir.joinpath(header)).exists():
            if not return_all:
                return joined
            ret.append(joined)
    if not ret:
        raise FileNotFoundError(f"{header} not found in search path")
    return ret


def main():
    """The main function"""
    args = _get_args()
    search_path = []
    if args.quoted:
        if args.quoted_includes is not None:
            search_path += args.quoted_includes
        search_path += quoted_search_dirs
    if args.includes is not None:
        search_path += args.includes
    search_path += default_search_dirs
    # add extra search directories
    for header in args.headers:
        if args.all_matches:
            for location in find_header(header, search_path, True):
                print(location)
        else:
            print(find_header(header, search_path, False))


if __name__ == "__main__":
    main()