Running Simulator inside asyncio eventloop and breaking out of `async for trigger: ...` causes runtime warning

[Sazzach]

I was writing a testcase in for a Glasgow applet, and my testbench emitted a bunch (~200) of warnings saying Task was destroyed but it is pending!

I did some investigation, and came up with the following minimal example:

import asyncio

from amaranth import *
from amaranth.sim import Simulator


def setup():
    m = Module()
    foo = Signal()
    m.d.sync += foo.eq(1)

    async def tb(ctx):
        async for _ in ctx.tick():
            break

    sim = Simulator(m)
    sim.add_clock(1e-6)
    sim.add_testbench(tb, background=False)
    sim.run()


async def async_setup():
    setup()


# no warning when running setup directly
#setup()
asyncio.new_event_loop().run_until_complete(async_setup())

Output:

samuelz@sz-t14 ~/D/g/async_for_test (main)> uv run --python 3.13 python -X tracemalloc asyncio_tb.py
<sys>:0: RuntimeWarning: coroutine method 'aclose' of 'TickTrigger.__aiter__' was never awaited
Object allocated at (most recent call last):
  File "/home/samuelz/Documents/glasgow_devel/async_for_test/asyncio_tb.py", lineno 13
    async for _ in ctx.tick():
Task was destroyed but it is pending!
task: <Task pending name='Task-2' coro=<<async_generator_athrow without __name__>()>>

If this isn't a issue with the simulator and running it within an asyncio event loop is unsupported I'd be happy to make a PR to Glasgow to fix it there.

[whitequark]

This is definitely intended to work but known to have some issues, see #1638.