_preflight.py

import os
import sys

from cupy_builder import Context


def preflight_check(ctx: Context) -> bool:
    source_root = ctx.source_root
    is_git = os.path.isdir(os.path.join(source_root, '.git'))
    for submodule in ('cupy/_core/include/cupy/cub',
                      'cupy/_core/include/cupy/jitify'):
        if 0 < len(os.listdir(os.path.join(source_root, submodule))):
            continue
        if is_git:
            msg = f'''
===========================================================================
The directory {submodule} is a git submodule but is currently empty.
Please use the command:

    $ git submodule update --init

to populate the directory before building from source.
===========================================================================
        '''
        else:
            msg = f'''
===========================================================================
The directory {submodule} is a git submodule but is currently empty.
Instead of using ZIP/TAR archive downloaded from GitHub, use

    $ git clone --recursive https://github.com/cupy/cupy.git

to get a buildable CuPy source tree.
===========================================================================
        '''

        print(msg, file=sys.stderr)
        return False
    return True