build/gen_cygpath.py

#
# Copyright (C) 2017 The Android Open Source Project
#
# 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.
#
"""Generates a make function approximating cygpath.

We don't just call cygpath (unless directed by NDK_USE_CYGPATH=1) because we
have to call this very often and doing so would be very slow. By doing this in
make, we can be much faster.
"""
from __future__ import print_function

import posixpath
import re
import sys


def get_mounts(mount_output):
    """Parses the output of mount and returns a dict of mounts.

    Args:
        mount_output: The text output from mount(1).

    Returns:
        A list of tuples mapping cygwin paths to Windows paths.
    """
    mount_regex = re.compile(r'^(\S+) on (\S+) .*$')

    # We use a list of tuples rather than a dict because we want to recurse on
    # the list later anyway.
    mounts = []
    for line in mount_output.splitlines():
        # Cygwin's mount doesn't use backslashes even in Windows paths, so no
        # need to replace here.
        match = mount_regex.search(line)
        if match is not None:
            win_path = match.group(1)
            cyg_path = match.group(2)
            if cyg_path == '/':
                # Since we're going to be using patsubst on these, we need to
                # make sure that the rule for / is applied last, otherwise
                # we'll replace all other cygwin paths with that one.
                mounts.insert(0, (cyg_path, win_path))
            elif cyg_path.startswith('/cygdrive/'):
                # We need both /cygdrive/c and /cygdrive/C to point to C:.
                letter = posixpath.basename(cyg_path)
                lower_path = posixpath.join('/cygdrive', letter.lower())
                upper_path = posixpath.join('/cygdrive', letter.upper())
                mounts.append((lower_path, win_path))
                mounts.append((upper_path, win_path))
            else:
                mounts.append((cyg_path, win_path))

    return mounts


def make_cygpath_function(mounts):
    """Creates a make function that can be used in place of cygpath.

    Args:
        mounts: A list of tuples decribing filesystem mounts.

    Returns:
        The body of a function implementing cygpath in make as a string.
    """
    # We're building a bunch of nested patsubst calls. Once we've written each
    # of the calls, we pass the function input to the inner most call.
    if not mounts:
        return '$1'

    cyg_path, win_path = mounts[0]
    if not cyg_path.endswith('/'):
        cyg_path += '/'
    if not win_path.endswith('/'):
        win_path += '/'

    other_mounts = mounts[1:]
    return '$(patsubst {}%,{}%,\n{})'.format(
        cyg_path, win_path, make_cygpath_function(other_mounts))


def main():
    # We're invoked from make and piped the output of `mount` so we can
    # determine what mappings to make.
    mount_output = sys.stdin.read()
    mounts = get_mounts(mount_output)
    print(make_cygpath_function(mounts))


if __name__ == '__main__':
    main()