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);
     }
eb218f459dc8a3139ef6e25f15c822463'>tree</a><a href='/guix/commit/gnu/packages/patches/ghc-testsuite-grep-compat.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>commit</a><a href='/guix/diff/gnu/packages/patches/ghc-testsuite-grep-compat.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/patches/ghc-testsuite-grep-compat.patch'>
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<div class='path'>path: <a href='/guix/log/?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>root</a>/<a href='/guix/log/gnu?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>gnu</a>/<a href='/guix/log/gnu/packages?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>packages</a>/<a href='/guix/log/gnu/packages/patches?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>patches</a>/<a href='/guix/log/gnu/packages/patches/ghc-testsuite-grep-compat.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463'>ghc-testsuite-grep-compat.patch</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/gnu/packages/patches/ghc-testsuite-grep-compat.patch?id=a14a94deb218f459dc8a3139ef6e25f15c822463&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-09-10 16:55:05 +0200'>2022-09-10</span></td><td><a href='/guix/commit/gnu/packages/patches/ghc-testsuite-grep-compat.patch?id=b4693f4a58b977c92282c81d3032f5be990e866a'>gnu: GHC: Adjust tests for grep 3.8.</a><span class='msg-avail'>...<span class='msg-tooltip'>This fixes a test failure introduced in commit
c527b0ce23c5d9228d29c5f90892aa5f05e77347.

* gnu/packages/patches/ghc-testsuite-grep-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/haskell.scm (ghc-8.6, ghc-8.8, ghc-8.10)[native-inputs]: Patch
the 'ghc-testsuite' input.
</span></span></td><td>Marius Bakke</td></tr>