hg-docker: fix Python 3.4 compatibility (for CentOS 7)

I realize Mercurial is not targetting Python 3.4 compatibility,
but without this change, it's not even possible to build it on
CentOS 7 (and I assume the same is true for RHEL 7).

Differential Revision: https://phab.mercurial-scm.org/D5570

contrib/packaging/hg-docker

@@ -1,111 +1,116 b''
 #!/usr/bin/env python3
 #
 # Copyright 2018 Gregory Szorc <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 import argparse
 import pathlib
 import shutil
 import subprocess
 import sys
 
 def get_docker() -> str:
     docker = shutil.which('docker.io') or shutil.which('docker')
     if not docker:
         print('could not find docker executable')
         return 1
 
     try:
         out = subprocess.check_output([docker, '-h'], stderr=subprocess.STDOUT)
 
         if b'Jansens' in out:
             print('%s is the Docking System Tray; try installing docker.io' %
                   docker)
             sys.exit(1)
     except subprocess.CalledProcessError as e:
         print('error calling `%s -h`: %s' % (docker, e.output))
         sys.exit(1)
 
     out = subprocess.check_output([docker, 'version'],
                                   stderr=subprocess.STDOUT)
 
     lines = out.splitlines()
     if not any(l.startswith((b'Client:', b'Client version:')) for l in lines):
         print('`%s version` does not look like Docker' % docker)
         sys.exit(1)
 
     if not any(l.startswith((b'Server:', b'Server version:')) for l in lines):
         print('`%s version` does not look like Docker' % docker)
         sys.exit(1)
 
     return docker
 
 def get_dockerfile(path: pathlib.Path, args: list) -> bytes:
     with path.open('rb') as fh:
         df = fh.read()
 
     for k, v in args:
         df = df.replace(b'%%%s%%' % k, v)
 
     return df
 
 def build_docker_image(dockerfile: pathlib.Path, params: list, tag: str):
     """Build a Docker image from a templatized Dockerfile."""
     docker = get_docker()
 
     dockerfile_path = pathlib.Path(dockerfile)
 
     dockerfile = get_dockerfile(dockerfile_path, params)
 
     print('building Dockerfile:')
     print(dockerfile.decode('utf-8', 'replace'))
 
     args = [
         docker,
         'build',
         '--build-arg', 'http_proxy',
         '--build-arg', 'https_proxy',
         '--tag', tag,
         '-',
     ]
 
     print('executing: %r' % args)
-    subprocess.run(args, input=dockerfile, check=True)
+    p = subprocess.Popen(args, stdin=subprocess.PIPE)
+    p.communicate(input=dockerfile)
+    if p.returncode:
+        raise subprocess.CalledProcessException(
+                p.returncode, 'failed to build docker image: %s %s' \
+                % (p.stdout, p.stderr))
 
 def command_build(args):
     build_args = []
     for arg in args.build_arg:
         k, v = arg.split('=', 1)
         build_args.append((k.encode('utf-8'), v.encode('utf-8')))
 
     build_docker_image(pathlib.Path(args.dockerfile),
                        build_args,
                        args.tag)
 
 def command_docker(args):
     print(get_docker())
 
 def main() -> int:
     parser = argparse.ArgumentParser()
 
     subparsers = parser.add_subparsers(title='subcommands')
 
     build = subparsers.add_parser('build', help='Build a Docker image')
     build.set_defaults(func=command_build)
     build.add_argument('--build-arg', action='append', default=[],
                         help='Substitution to perform in Dockerfile; '
                              'format: key=value')
     build.add_argument('dockerfile', help='path to Dockerfile to use')
     build.add_argument('tag', help='Tag to apply to created image')
 
     docker = subparsers.add_parser('docker-path', help='Resolve path to Docker')
     docker.set_defaults(func=command_docker)
 
     args = parser.parse_args()
 
     return args.func(args)
 
 if __name__ == '__main__':
     sys.exit(main())