ISSUE-1585 | Surface fontTools logs for easier investigation

[kdipippo]

Work-in-progress.

Taking the feedback from the following 2 issues into this PR:

• 'created' timestamp seems very low; regarding as unix timestamp #1585
• How to capture log.warnings() produced from erroring fonts / properly check fonts fonttools/fonttools#3538

[liZe]

After thinking about the best way to solve this issue, here’s what seems to be the best solution for me.

The code needed to capture logs is already in WeasyPrint: it’s used for tests, to check that we get no warning or the intended warning messages, depending on the test.

WeasyPrint/tests/testing_utils.py

Lines 73 to 100 in 6e93e95

	class CallbackHandler(logging.Handler):
	"""A logging handler that calls a function for every message."""
	def __init__(self, callback):
	logging.Handler.__init__(self)
	self.emit = callback
	@contextlib.contextmanager
	def capture_logs():
	"""Return a context manager that captures all logged messages."""
	logger = LOGGER
	messages = []
	def emit(record):
	if record.name == 'weasyprint.progress':
	return
	messages.append(f'{record.levelname.upper()}: {record.getMessage()}')
	previous_handlers = logger.handlers
	previous_level = logger.level
	logger.handlers = []
	logger.addHandler(CallbackHandler(emit))
	logger.setLevel(logging.DEBUG)
	try:
	yield messages
	finally:
	logger.handlers = previous_handlers
	logger.level = previous_level

What we could do is:

• Move CallbackHandler and capture_logs to logger.py.
• Add a parameter to capture_logs to define the logger we want to capture. Its default value would be 'weasyprint' to keep the current default behaviour.
• Use with capture_logs('fontTools') as logs: around the call to subsetter.subset() and display the logs thanks to LOGGER.warning(), just as you did in your PR.

What do you think of this solution?

As the code has changed a bit in main, you should probably create a new branch from main, create a new commit and push force to your branch.

[liZe]

I’ve fixed the problem in 61852c4. Thanks a lot for your investigation and for your proposal. 💜