Issue #19176: Fixed doctype() related bugs in C implementation of ElementTree.

A deprecation warning no longer issued by XMLParser subclass with default
doctype() method.  Direct call of doctype() now issues a warning.  Parser's
doctype() now is not called if target's doctype() is called.  Based on patch
by Martin Panter.

Lib/test/test_xml_etree.py

@@ -12,6 +12,7 @@ import pickle
 import sys
 import types
 import unittest
+import warnings
 import weakref
 
 from itertools import product
@@ -2237,6 +2238,20 @@ class XMLParserTest(unittest.TestCase):
         parser.feed(self.sample1)
         self._check_sample_element(parser.close())
 
+    def test_doctype_warning(self):
+        parser = ET.XMLParser()
+        with self.assertWarns(DeprecationWarning):
+            parser.doctype('html', '-//W3C//DTD XHTML 1.0 Transitional//EN',
+                'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd')
+        parser.feed('<html/>')
+        parser.close()
+
+        with warnings.catch_warnings():
+            warnings.simplefilter('error', DeprecationWarning)
+            parser = ET.XMLParser()
+            parser.feed(self.sample2)
+            parser.close()
+
     def test_subclass_doctype(self):
         _doctype = None
         class MyParserWithDoctype(ET.XMLParser):
@@ -2252,6 +2267,32 @@ class XMLParserTest(unittest.TestCase):
             ('html', '-//W3C//DTD XHTML 1.0 Transitional//EN',
              'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'))
 
+        _doctype = _doctype2 = None
+        with warnings.catch_warnings():
+            warnings.simplefilter('error', DeprecationWarning)
+            class DoctypeParser:
+                def doctype(self, name, pubid, system):
+                    nonlocal _doctype2
+                    _doctype2 = (name, pubid, system)
+
+            parser = MyParserWithDoctype(target=DoctypeParser())
+            parser.feed(self.sample2)
+            parser.close()
+            self.assertIsNone(_doctype)
+            self.assertEqual(_doctype2,
+                ('html', '-//W3C//DTD XHTML 1.0 Transitional//EN',
+                 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'))
+
+    def test_inherited_doctype(self):
+        '''Ensure that ordinary usage is not deprecated (Issue 19176)'''
+        with warnings.catch_warnings():
+            warnings.simplefilter('error', DeprecationWarning)
+            class MyParserWithoutDoctype(ET.XMLParser):
+                pass
+            parser = MyParserWithoutDoctype()
+            parser.feed(self.sample2)
+            parser.close()
+
     def test_parse_string(self):
         parser = ET.XMLParser(target=ET.TreeBuilder())
         parser.feed(self.sample3)

Misc/NEWS

@@ -64,6 +64,12 @@ Core and Builtins
 Library
 -------
 
+- Issue #19176: Fixed doctype() related bugs in C implementation of ElementTree.
+  A deprecation warning no longer issued by XMLParser subclass with default
+  doctype() method.  Direct call of doctype() now issues a warning.  Parser's
+  doctype() now is not called if target's doctype() is called.  Based on patch
+  by Martin Panter.
+
 - Issue #20387: Restore semantic round-trip correctness in tokenize/untokenize
   for tab-indented blocks.
 

Modules/_elementtree.c

@@ -2791,7 +2791,7 @@ typedef struct {
 
 } XMLParserObject;
 
-#define XMLParser_CheckExact(op) (Py_TYPE(op) == &XMLParser_Type)
+static PyObject* xmlparser_doctype(XMLParserObject* self, PyObject* args);
 
 /* helpers */
 
@@ -3190,20 +3190,21 @@ expat_start_doctype_handler(XMLParserObject *self,
                                     doctype_name_obj, pubid_obj, sysid_obj);
         Py_CLEAR(res);
     }
-
-    /* Now see if the parser itself has a doctype method. If yes and it's
-     * a subclass, call it but warn about deprecation. If it's not a subclass
-     * (i.e. vanilla XMLParser), do nothing.
-     */
-    parser_doctype = PyObject_GetAttrString(self_pyobj, "doctype");
-    if (parser_doctype) {
-        if (!XMLParser_CheckExact(self_pyobj)) {
-            if (PyErr_WarnEx(PyExc_DeprecationWarning,
-                            "This method of XMLParser is deprecated.  Define"
-                            " doctype() method on the TreeBuilder target.",
-                            1) < 0) {
+    else {
+        /* Now see if the parser itself has a doctype method. If yes and it's
+         * a custom method, call it but warn about deprecation. If it's only
+         * the vanilla XMLParser method, do nothing.
+         */
+        parser_doctype = PyObject_GetAttrString(self_pyobj, "doctype");
+        if (parser_doctype &&
+            !(PyCFunction_Check(parser_doctype) &&
+              PyCFunction_GET_SELF(parser_doctype) == self_pyobj &&
+              PyCFunction_GET_FUNCTION(parser_doctype) ==
+                    (PyCFunction) xmlparser_doctype)) {
+            res = xmlparser_doctype(self, NULL);
+            if (!res)
                 goto clear;
-            }
+            Py_DECREF(res);
             res = PyObject_CallFunction(parser_doctype, "OOO",
                                         doctype_name_obj, pubid_obj, sysid_obj);
             Py_CLEAR(res);
@@ -3556,6 +3557,12 @@ xmlparser_parse_whole(XMLParserObject* self, PyObject* args)
 static PyObject*
 xmlparser_doctype(XMLParserObject *self, PyObject *args)
 {
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "This method of XMLParser is deprecated.  Define"
+                     " doctype() method on the TreeBuilder target.",
+                     1) < 0) {
+        return NULL;
+    }
     Py_RETURN_NONE;
 }