bazel_rules_fuchsia/fuchsia/tools/unbuffer.py

#!/usr/bin/env python3
# Copyright 2023 The Fuchsia Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

import os
import pty
import subprocess
import sys

from typing import List

def main(command: List[str]) -> int:
    try:
        if sys.stdout.isatty() and sys.stderr.isatty():
            return subprocess.run(command).returncode
        else:
            # http://fxbug.dev/119214: Force process not to buffer by faking a tty.
            # Running test targets in a non-tty environment (eg: via `bazel run`,
            # `bazel test`, or via infra) implicitly enables stdout buffering for all
            # subprocesses while leaving stderr unbuffered, causing stderr/stdout to
            # appear out of order.
            # We emulate a tty here in order to fix this.
            host_fd, child_fd = pty.openpty()
            os.environ['NO_COLOR'] = '1'
            proc = subprocess.Popen(command, stdout=child_fd, stderr=child_fd)
            os.close(child_fd)

            while True:
                try:
                    stdout = os.read(host_fd, 1024).decode('utf-8')
                    sys.stdout.write(stdout)
                    sys.stdout.flush()
                except OSError:
                    break
                if not stdout:
                    break

            return proc.wait()
    except KeyboardInterrupt:
        pass

if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))