asyncio subprocess spawn does not record the awaiting task

[deadlovelll]

Bug report

Bug description:

The internal subprocess pipe-connect task registers no awaited_by edge

Repro:

import asyncio, sys

async def main():
    spawn = asyncio.create_task(
        asyncio.create_subprocess_exec(sys.executable, '-c', 'pass',
                                       stdin=asyncio.subprocess.PIPE),
        name='spawn')

    await asyncio.sleep(0)
    await asyncio.sleep(0)

    for t in asyncio.all_tasks() - {asyncio.current_task()}:
        asyncio.print_call_graph(t)

    proc = await spawn
    await proc.wait()

asyncio.run(main())

Actual:

* Task(name='spawn', id=0x103e00b90)
  + Call stack:
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()
* Task(name='Task-2', id=0x103b7d0a0)
  + Call stack:
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1753, in async BaseEventLoop.connect_write_pipe()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_subprocess.py', line 188, in async BaseSubprocessTransport._connect_pipes()

Expected:

* Task(name='spawn', id=0x105620b90)
  + Call stack:
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()
* Task(name='Task-2', id=0x10539d0a0)
  + Call stack:
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1753, in async BaseEventLoop.connect_write_pipe()
  |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_subprocess.py', line 194, in async BaseSubprocessTransport._connect_pipes()
  + Awaited by:
    * Task(name='spawn', id=0x105620b90)
      + Call stack:
      |   File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
      |   File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
      |   File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()

Proposed fix: register the edge in BaseSubprocessTransport.__init__ and discard it in doe callback

I have a fix ready for that

CPython versions tested on:

CPython main branch

Operating systems tested on:

macOS

[kumaraditya303]

There is little value in recording for internal tasks

[deadlovelll]

There is little value in recording for internal tasks

The docs say no exception for internal tasks (ascynio-graph.rst:125) :

Any time an intermediate :class:`Future` object with low-level APIs like
:meth:`Future.add_done_callback() <asyncio.Future.add_done_callback>` is
involved, the following two functions should be used to inform asyncio
about how exactly such intermediate future objects are connected with
the tasks they wrap or control.

For example we have same bookkeeping in staggered_race() for its internal run_one_coro tasks

So i think this should be supported too