This patch fixes a crash in the libxml2 bindings for Python 3.x
that 'itstool' stumbles upon when processing UTF-8 data:

  https://issues.guix.gnu.org/issue/37468

Patch by Jan Matejek
from <https://bugzilla.opensuse.org/show_bug.cgi?id=1065270>.

--- libxml2-2.9.5.orig/python/libxml.c
+++ libxml2-2.9.5/python/libxml.c
@@ -1620,6 +1620,7 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
     PyObject *message;
     PyObject *result;
     char str[1000];
+    unsigned char *ptr = (unsigned char *)str;
 
 #ifdef DEBUG_ERROR
     printf("libxml_xmlErrorFuncHandler(%p, %s, ...) called\n", ctx, msg);
@@ -1636,12 +1637,20 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
 	    str[999] = 0;
         va_end(ap);
 
+#if PY_MAJOR_VERSION >= 3
+        /* Ensure the error string doesn't start at UTF8 continuation. */
+        while (*ptr && (*ptr & 0xc0) == 0x80)
+            ptr++;
+#endif
+
         list = PyTuple_New(2);
         PyTuple_SetItem(list, 0, libxml_xmlPythonErrorFuncCtxt);
         Py_XINCREF(libxml_xmlPythonErrorFuncCtxt);
-        message = libxml_charPtrConstWrap(str);
+        message = libxml_charPtrConstWrap(ptr);
         PyTuple_SetItem(list, 1, message);
         result = PyEval_CallObject(libxml_xmlPythonErrorFuncHandler, list);
+        /* Forget any errors caused in the error handler. */
+        PyErr_Clear();
         Py_XDECREF(list);
         Py_XDECREF(result);
     }
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<div class='path'>path: <a href='/guix/log/?id=525e83ec83eca8d555913e59235902fa635b052d'>root</a>/<a href='/guix/log/.gitignore?id=525e83ec83eca8d555913e59235902fa635b052d'>.gitignore</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/.gitignore?id=525e83ec83eca8d555913e59235902fa635b052d&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-30 12:24:55 +0200'>2020-03-30</span></td><td><a href='/guix/commit/.gitignore?id=6e27d1088da07380872f0df9f308b674536cefc8'>.gitignore: Ignore test results in tests/services.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-03-11 02:45:33 +0100'>2020-03-11</span></td><td><a href='/guix/commit/.gitignore?id=73fbe04107d38f4561636c74d28d7a4935cbb1ef'>Add system start-up files for guix-daemon.</a><span class='msg-avail'>...</span></td><td>Danny Milosavljevic</td></tr>
<tr><td><span title='2019-09-24 10:11:38 +0200'>2019-09-24</span></td><td><a href='/guix/commit/.gitignore?id=11da634a6e64afa2904542e2174aa2a185f9ac3a'>Merge branch 'master' into core-updates</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-18 11:38:14 +0200'>2019-09-18</span></td><td><a href='/guix/commit/.gitignore?id=7bc46ecc34ceb042ff890e5d306d0a2a736e891d'>doc: Add Guix Cookbook.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-06-14 22:09:38 +0200'>2019-06-14</span></td><td><a href='/guix/commit/.gitignore?id=92d00ca4661e186022732a47956a2bc0ef16be96'>build: Remove 'gnu/packages/bootstrap' and its binaries.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-26 11:21:32 +0200'>2019-04-26</span></td><td><a href='/guix/commit/.gitignore?id=9ca5ff882e2ac4eaab02eb0fde545bd784af478b'>bootstrap: Break automake dependency on generated files.</a><span class='msg-avail'>...</span></td><td>Miguel Ángel Arruga Vivas</td></tr>
<tr><td><span title='2018-11-20 01:42:43 +0100'>2018-11-20</span></td><td><a href='/guix/commit/.gitignore?id=975b7966f592993bce04e3c153f52f2ece402f21'>.gitignore: Re-add 'authenticate' script.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-06-14 11:17:00 +0200'>2018-06-14</span></td><td><a href='/guix/commit/.gitignore?id=ea0a06cee2ba05451f94714a4f913db02efbe92c'>Remove 'guix-register' and its traces.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-06-12 15:23:34 +0200'>2018-06-12</span></td><td><a href='/guix/commit/.gitignore?id=5909bdc88735c2c1bd9f44eb6a1b518785144292'>.gitignore: Add doc/stamp-[0-9].</a></td><td>Ludovic Courtès</td></tr>