Bug#962197: buildstream: Event loop broken on Python 3.8

[Ben Hutchings]

Package: buildstream
Version: 1.4.1-1
Severity: grave

Dear Maintainer,

Un-cached builds with builstream currently fail like this:

[--:--:--][][] BUG     no running event loop

    Traceback (most recent call last):
      File "/usr/bin/bst", line 8, in <module>
        sys.exit(cli())
      File "/usr/lib/python3/dist-packages/click/core.py", line 764, in __call__
        return self.main(*args, **kwargs)
      File "/usr/lib/python3/dist-packages/buildstream/_frontend/cli.py", line 173, in override_main
        original_main(self, args=args, prog_name=prog_name, complete_var=None,
      File "/usr/lib/python3/dist-packages/click/core.py", line 717, in main
        rv = self.invoke(ctx)
      File "/usr/lib/python3/dist-packages/click/core.py", line 1137, in invoke
        return _process_result(sub_ctx.command.invoke(sub_ctx))
      File "/usr/lib/python3/dist-packages/click/core.py", line 956, in invoke
        return ctx.invoke(self.callback, **ctx.params)
      File "/usr/lib/python3/dist-packages/click/core.py", line 555, in invoke
        return callback(*args, **kwargs)
      File "/usr/lib/python3/dist-packages/click/decorators.py", line 27, in new_func
        return f(get_current_context().obj, *args, **kwargs)
      File "/usr/lib/python3/dist-packages/buildstream/_frontend/cli.py", line 340, in build
        app.stream.build(elements,
      File "/usr/lib/python3/dist-packages/buildstream/_stream.py", line 211, in build
        self._run()
      File "/usr/lib/python3/dist-packages/buildstream/_stream.py", line 1022, in _run
        _, status = self._scheduler.run(self.queues)
      File "/usr/lib/python3/dist-packages/buildstream/_scheduler/scheduler.py", line 153, in run
        self._sched()
      File "/usr/lib/python3/dist-packages/buildstream/_scheduler/scheduler.py", line 427, in _sched
        self._sched_queue_jobs()
      File "/usr/lib/python3/dist-packages/buildstream/_scheduler/scheduler.py", line 401, in _sched_queue_jobs
        self._spawn_job(job)
      File "/usr/lib/python3/dist-packages/buildstream/_scheduler/scheduler.py", line 281, in _spawn_job
        job.spawn()
      File "/usr/lib/python3/dist-packages/buildstream/_scheduler/jobs/job.py", line 162, in spawn
        self._watcher.add_child_handler(self._process.pid, self._parent_child_completed)
      File "/usr/lib/python3.8/asyncio/unix_events.py", line 1293, in add_child_handler
        loop = events.get_running_loop()
    RuntimeError: no running event loop

This was reported upstream as:
https://gitlab.com/BuildStream/buildstream/-/issues/1246

but is now tracked in:
https://gitlab.com/BuildStream/buildstream/-/issues/1173

Ben.

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.19.0-9-amd64 (SMP w/2 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages buildstream depends on:
ii  python3              3.8.2-3
ii  python3-buildstream  1.4.1-1

Versions of packages buildstream recommends:
ii  python3-bst-external  0.18.0-1

buildstream suggests no packages.

-- no debconf information

-- 
Ben Hutchings, Software Developer                         Codethink Ltd
https://www.codethink.co.uk/                 Dale House, 35 Dale Street
                                     Manchester, M1 2HF, United Kingdom