FIX: Gracefully handle bad XML files in EGI reader

[scott-huberty]

I have a few MFF files which contain a corrupt XML file (a tag didn't close properly).

This PR uses defensive programming to gracefully handle the scenario, while also providing more information to the user about the XML file that couldn't be parsed.

from pathlib import Path
import mne
import shutil
egi_fname = mne.datasets.testing.data_path() / "EGI" / "test_egi.mff"

test_fname = shutil.copytree(egi_fname, Path("./bad_xml_egi.mff").resolve())
bad_xml = test_fname / "bad.xml"
bad_xml.write_text("<bad>")
raw = mne.io.read_raw_egi(test_fname)
test_fname.unlink()

on main (crashes and doesn't give a hint)

Reading EGI MFF Header from /Users/scotterik/devel/repos/mne-python/bad_xml_egi.mff...
    Reading events ...
Traceback (most recent call last):

  File ~/.local/share/uv/python/cpython-3.10.16-macos-x86_64-none/lib/python3.10/xml/etree/ElementTree.py:1725 in close
    self.parser.Parse(b"", True) # end of data

ExpatError: no element found: line 1, column 5


During handling of the above exception, another exception occurred:

Traceback (most recent call last):

  File ~/devel/projects/IBIS-EEG/.venv/lib/python3.10/site-packages/IPython/core/interactiveshell.py:3577 in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)

  Cell In[4], line 9
    raw = mne.io.read_raw_egi(test_fname)

  File <decorator-gen-359>:12 in read_raw_egi

  File ~/devel/repos/mne-python/mne/io/egi/egi.py:175 in read_raw_egi
    return _read_raw_egi_mff(

  File <decorator-gen-356>:12 in _read_raw_egi_mff

  File ~/devel/repos/mne-python/mne/io/egi/egimff.py:361 in _read_raw_egi_mff
    return RawMff(

  File <decorator-gen-357>:12 in __init__

  File ~/devel/repos/mne-python/mne/io/egi/egimff.py:411 in __init__
    egi_events, egi_info, mff_events = _read_events(input_fname, egi_info)

  File ~/devel/repos/mne-python/mne/io/egi/events.py:26 in _read_events
    mff_events, event_codes = _read_mff_events(input_fname, info["sfreq"])

  File ~/devel/repos/mne-python/mne/io/egi/events.py:51 in _read_mff_events
    orig[xml_type] = _parse_xml(xml_file)

  File ~/devel/repos/mne-python/mne/io/egi/events.py:86 in _parse_xml
    xml = defusedxml.ElementTree.parse(xml_file)

  File ~/devel/projects/IBIS-EEG/.venv/lib/python3.10/site-packages/defusedxml/common.py:100 in parse
    return _parse(source, parser)

  File ~/.local/share/uv/python/cpython-3.10.16-macos-x86_64-none/lib/python3.10/xml/etree/ElementTree.py:1222 in parse
    tree.parse(source, parser)

  File ~/.local/share/uv/python/cpython-3.10.16-macos-x86_64-none/lib/python3.10/xml/etree/ElementTree.py:587 in parse
    self._root = parser.close()

  File ~/.local/share/uv/python/cpython-3.10.16-macos-x86_64-none/lib/python3.10/xml/etree/ElementTree.py:1727 in close
    self._raiseerror(v)

  File ~/.local/share/uv/python/cpython-3.10.16-macos-x86_64-none/lib/python3.10/xml/etree/ElementTree.py:1627 in _raiseerror
    raise err

  File <string>
ParseError: no element found: line 1, column 5

this branch:

Reading EGI MFF Header from /Users/scotterik/devel/repos/mne-python/bad_xml_egi.mff...
    Reading events ...
<ipython-input-17-ca7d688fd187>:1: RuntimeWarning: Could not parse the XML file /Users/scotterik/devel/repos/mne-python/bad_xml_egi.mff/bad.xml.
  raw = mne.io.read_raw_egi(test_fname)
    Assembling measurement info ...
    Excluding events {} ...

[scott-huberty]

Needs #13146 (or some other fix for the failing ubuntu-latest CI)

[larsoner]

Okay let's wait for #13146 then and then we can click the Update button on this PR. In the meantime I'll mark for merge-when-green, thanks in advance @scott-huberty !