[feaLib] Fails when running with multiprocessing #3762
Description
I'm compiling OTL features with feaLib (addOpenTypeFeaturesFromString) in a multiprocessing.Pool.
Whenever the feature compilation fails, I get this traceback instead of the location in the feature file where the error actually is:
Exception in thread Thread-3 (_handle_results):
Traceback (most recent call last):
File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/threading.py", line 1041, in _bootstrap_inner
self.run()
~~~~~~~~^^
File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/threading.py", line 992, in run
self._target(*self._args, **self._kwargs)
~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/multiprocessing/pool.py", line 579, in _handle_results
task = get()
File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/multiprocessing/connection.py", line 251, in recv
return _ForkingPickler.loads(buf.getbuffer())
~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
TypeError: FeatureLibError.__init__() missing 1 required positional argument: 'location'
... and I need to quit manually (ctrl-c).
When I run it in a normal environment, the error is printed correctly, and the script exits:
File "site-packages/fontTools/feaLib/parser.py", line 349, in parse_glyphclass_
raise FeatureLibError(
...<2 lines>...
)
fontTools.feaLib.error.FeatureLibError: <features>:104:13: Unknown glyph class @_A_1st
How can I avoid the hanging process in multiprocessing, and get it to print the correct error message?