RelaxNG validation does not report all errors in the log

[Audric Schiltknecht]

The attached XML fails validation with provided RNG schema when using xmllint:

$ xmllint --noout --relaxng test.rng test.xml
test.xml:6: element data: validity error : IDREF attribute ref references an unknown ID "myref"
test.xml fails to validate

However, when using lxml, there is no error returned (validation still fail as expected):

>>> from lxml import etree
>>> rng = etree.RelaxNG(file="test.rng")
>>> rng.validate(etree.parse("test.xml"))
False
>>> rng.error_log

>>>

I've managed to figure out that libxml uses the xmlGenericError function at this point to trace this error, and lxm disables generic errors.
If I temporarily re-enable generic error by commenting out line 28 of src/lxml/xmlerror.pxi (first line of code of the _initThreadLogging() function), I can see the log message as a trace in my console:

>>> rng.validate(etree.parse("test.xml"))
IDREF attribute ref references an unknown ID "myref"
False

---------------------
Software Versions:

Python : sys.version_info(major=3, minor=5, micro=0, releaselevel='final', serial=0)
lxml.etree : (3, 5, 0, 0)
libxml used : (2, 9, 3)
libxml compiled : (2, 9, 3)
libxslt used : (1, 1, 28)
libxslt compiled : (1, 1, 28)

[scoder (scoder)]

Good catch. Fixed here:
https://github.com/lxml/lxml/commit/c7ae47731a1c017ce64f93784cc82034e0669169