Bug in run_cmd_with_timeout means you always get an error about `ls -d` timing out

[Timmmm]

If the SCRATCH_ROOT env var is set you hit this code:

dvsim/src/dvsim/cli/run.py

Lines 62 to 72 in 0f13466

	if scratch_root is None:
	arg_scratch_root = default_scratch_root
	else:
	# Scratch space could be mounted in a filesystem (such as NFS) on a network drive.
	# If the network is down, it could cause the access access check to hang. So run a
	# simple ls command with a timeout to prevent the hang.
	(out, status) = run_cmd_with_timeout(
	cmd="ls -d " + scratch_root,
	timeout=1,
	exit_on_failure=0,
	)

That calls this function:

dvsim/src/dvsim/utils/subprocess.py

Lines 28 to 39 in 0f13466

	def run_cmd_with_timeout(
	cmd: str,
	*,
	timeout: float | None = None,
	exit_on_failure: bool = True,
	) -> tuple[str, int]:
	"""Run a command with a specified timeout.
	If the command does not finish before the timeout, then it returns -1. Else
	it returns the command output. If the command fails, it throws an exception
	and returns the stderr.
	"""

(With the wrong type for exit_on_failure btw, but who needs correct types?)

The problem is that function will basically always say that the command has timed out. The bug is due to the classic truthiness footgun that Python shares with Javascript. Unlike in Typescript where you can (with considerable effort) set up ESLint to ban truthiness bugs, I'm not aware of a way to do that in Python so you just have to be vigilant.

Here is the bug (and the other poll further down):

dvsim/src/dvsim/utils/subprocess.py

Lines 53 to 54 in 0f13466

	if p.poll():
	break

It needs to be if p.poll() is not None:.

poll() returns the exit code or None if the process has not exited. If the command succeeds then p.poll() returns 0, and if 0: will never succeed so it thinks the command times out.

[Timmmm]

Fix here: f89a191