pre-commit-hooks/pre_commit_hooks/trailing_whitespace_fixer.py

from __future__ import annotations

import argparse
import os
from collections.abc import Sequence


def _fix_file(
        filename: str,
        is_markdown: bool,
        chars: bytes | None,
) -> bool:
    with open(filename, mode='rb') as file_processed:
        lines = file_processed.readlines()
    newlines = [_process_line(line, is_markdown, chars) for line in lines]
    if newlines != lines:
        with open(filename, mode='wb') as file_processed:
            for line in newlines:
                file_processed.write(line)
        return True
    else:
        return False


def _process_line(
        line: bytes,
        is_markdown: bool,
        chars: bytes | None,
) -> bytes:
    if line[-2:] == b'\r\n':
        eol = b'\r\n'
        line = line[:-2]
    elif line[-1:] == b'\n':
        eol = b'\n'
        line = line[:-1]
    else:
        eol = b''
    # preserve trailing two-space for non-blank lines in markdown files
    if is_markdown and (not line.isspace()) and line.endswith(b'  '):
        return line[:-2].rstrip(chars) + b'  ' + eol
    return line.rstrip(chars) + eol


def main(argv: Sequence[str] | None = None) -> int:
    parser = argparse.ArgumentParser()
    parser.add_argument(
        '--no-markdown-linebreak-ext',
        action='store_true',
        help=argparse.SUPPRESS,
    )
    parser.add_argument(
        '--markdown-linebreak-ext',
        action='append',
        default=[],
        metavar='*|EXT[,EXT,...]',
        help=(
            'Markdown extensions (or *) to not strip linebreak spaces.  '
            'default: %(default)s'
        ),
    )
    parser.add_argument(
        '--chars',
        help=(
            'The set of characters to strip from the end of lines.  '
            'Defaults to all whitespace characters.'
        ),
    )
    parser.add_argument('filenames', nargs='*', help='Filenames to fix')
    args = parser.parse_args(argv)

    if args.no_markdown_linebreak_ext:
        print('--no-markdown-linebreak-ext now does nothing!')

    md_args = args.markdown_linebreak_ext
    if '' in md_args:
        parser.error('--markdown-linebreak-ext requires a non-empty argument')
    all_markdown = '*' in md_args
    # normalize extensions; split at ',', lowercase, and force 1 leading '.'
    md_exts = [
        '.' + x.lower().lstrip('.') for x in ','.join(md_args).split(',')
    ]

    # reject probable "eaten" filename as extension: skip leading '.' with [1:]
    for ext in md_exts:
        if any(c in ext[1:] for c in r'./\:'):
            parser.error(
                f'bad --markdown-linebreak-ext extension '
                f'{ext!r} (has . / \\ :)\n'
                f"  (probably filename; use '--markdown-linebreak-ext=EXT')",
            )
    chars = None if args.chars is None else args.chars.encode()
    return_code = 0
    for filename in args.filenames:
        _, extension = os.path.splitext(filename.lower())
        md = all_markdown or extension in md_exts
        if _fix_file(filename, md, chars):
            print(f'Fixing {filename}')
            return_code = 1
    return return_code


if __name__ == '__main__':
    raise SystemExit(main())