Guest fact discovery via a single script

[happz]

TL;DR: guest fact discovery now runs as a single remote command, whose
output is then parsed into values of individual facts.

• Each fact attribute is now defined with a descriptor (see [1]). It
  keeps the proper type annotation, but we can attach more information.
• Each probe is now a shell script snippet, and is attached to its
  owning fact.
• Snippets are collected, joined, and the resulting script is executed.
  GuestFacts then processes the output, delivers discovered values to
  the right attributes.
• No Python code in probes, custom Python code to handle decoding of the
  script output fully supported (and used, see package manager facts).

For the tmt code, nothing changes, GuestFacts API remains the same.

[1] https://docs.python.org/3/howto/descriptor.html

Pull Request Checklist

• implement the feature
• write the documentation

[happz]

Blocked on #4443

[graphite-app]

The is_image_mode fact has a logic error that will incorrectly return true when the bootc status command fails. If sudo bootc status fails (due to permission issues, bootc errors, etc.), the command substitution returns an empty string, making the comparison [ "" = "image: null" ] evaluate to false, which causes the else branch to execute and echo 'true'. This is incorrect - a failure should result in 'false' or 'unknown'.

# Fix: Check command success explicitly
is_image_mode = flag_guest_fact(
    """
    if type bootc 1>&2; then
        image=$(sudo bootc status --format yaml 2>/dev/null | grep '^image:' | cut -d' ' -f2)
        if [ -n "$image" ] && [ "$image" != "null" ]; then
            echo 'true'
        else
            echo 'false'
        fi
    else
        echo 'false'
    fi
    """
)

Suggested change

	is_image_mode = flag_guest_fact(
	"""
	if type bootc 1>&2; then
	if [ "$(sudo bootc status --format yaml | grep image:)" = "image: null" ]; then
	echo 'false'
	else
	echo 'true'
	fi
	else
	echo 'false'
	fi
	"""
	)
	is_image_mode = flag_guest_fact(
	"""
	if type bootc 1>&2; then
	image=$(sudo bootc status --format yaml 2>/dev/null | grep '^image:' | cut -d' ' -f2)
	if [ -n "$image" ] && [ "$image" != "null" ]; then
	echo 'true'
	else
	echo 'false'
	fi
	else
	echo 'false'
	fi
	"""
	)

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[graphite-app]

Missing validation for unclosed fact markers. If the output ends while current_fact is still set (opened with >>> but never closed with <<<), the method silently loses that fact's data without raising an error. This could happen if a probe script fails mid-execution or produces malformed output.

# Add after the for loop, before return:
if current_fact is not None:
    raise GeneralError(
        f"Malformed fact probe output: fact '{current_fact}' was opened but never closed"
    )

Suggested change

	for line in output.splitlines():
	line = line.strip()
	if output is None or output.stdout is None:
	return None
	if line.startswith('>>> '):
	current_fact = line[4:]
	return output.stdout.strip() == 'root'
	elif line.startswith('<<<'):
	if current_fact is None:
	raise GeneralError(
	"Malformed fact probe output: closing marker '<<<' without opening marker"
	)
	def _query_can_sudo(self, guest: 'Guest') -> Optional[bool]:
	try:
	guest.execute(Command("sudo", "-n", "true"), silent=True)
	except tmt.utils.RunError:
	# Failed non-interactive sudo, so we can't sudo
	return False
	# Otherwise we may use sudo
	return True
	facts[current_fact] = self._facts()[current_fact].extract(
	'\n'.join(current_fact_content)
	)
	def _query_sudo_prefix(self, guest: 'Guest') -> Optional[str]:
	# Note: we cannot reuse `is_superuser` or `can_sudo` fact so we just recall the query
	# functions for now
	if self._query_is_superuser(guest):
	# Root user does not need sudo
	return ""
	if self._query_can_sudo(guest):
	return "sudo"
	return ""
	def _query_is_ostree(self, guest: 'Guest') -> Optional[bool]:
	# https://github.com/vrothberg/chkconfig/commit/538dc7edf0da387169d83599fe0774ea080b4a37#diff-562b9b19cb1cd12a7343ce5c739745ebc8f363a195276ca58e926f22927238a5R1334
	output = self._execute(
	guest,
	ShellScript(
	"""
	( [ -e /run/ostree-booted ] || [ -L /ostree ] ) && echo yes || echo no
	"""
	).to_shell_command(),
	)
	current_fact = None
	current_fact_content = []
	if output is None or output.stdout is None:
	return None
	else:
	current_fact_content.append(line)
	return output.stdout.strip() == 'yes'
	return facts
	for line in output.splitlines():
	line = line.strip()
	if line.startswith('>>> '):
	current_fact = line[4:]
	elif line.startswith('<<<'):
	if current_fact is None:
	raise GeneralError(
	"Malformed fact probe output: closing marker '<<<' without opening marker"
	)
	facts[current_fact] = self._facts()[current_fact].extract(
	'\n'.join(current_fact_content)
	)
	current_fact = None
	current_fact_content = []
	else:
	current_fact_content.append(line)
	if current_fact is not None:
	raise GeneralError(
	f"Malformed fact probe output: fact '{current_fact}' was opened but never closed"
	)
	return facts

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