Fix #7610: incorrectly renders consecutive backslashes

CHANGES

@@ -89,6 +89,7 @@ Bugs fixed
 * #7536: sphinx-autogen: crashes when template uses i18n feature
 * #2785: html: Bad alignment of equation links
 * #7581: napoleon: bad parsing of inline code in attribute docstrings
+* #7610: incorrectly renders consecutive backslashes for docutils-0.16
 
 Testing
 --------

sphinx/transforms/__init__.py

@@ -23,6 +23,7 @@ from sphinx import addnodes
 from sphinx.config import Config
 from sphinx.deprecation import RemovedInSphinx40Warning, deprecated_alias
 from sphinx.locale import _, __
+from sphinx.util import docutils
 from sphinx.util import logging
 from sphinx.util.docutils import new_document
 from sphinx.util.i18n import format_date
@@ -360,12 +361,18 @@ class SphinxSmartQuotes(SmartQuotes, SphinxTransform):
     def get_tokens(self, txtnodes: List[Text]) -> Generator[Tuple[str, str], None, None]:
         # A generator that yields ``(texttype, nodetext)`` tuples for a list
         # of "Text" nodes (interface to ``smartquotes.educate_tokens()``).
-
-        texttype = {True: 'literal',  # "literal" text is not changed:
-                    False: 'plain'}
         for txtnode in txtnodes:
-            notsmartquotable = not is_smartquotable(txtnode)
-            yield (texttype[notsmartquotable], txtnode.astext())
+            if is_smartquotable(txtnode):
+                if docutils.__version_info__ >= (0, 16):
+                    # SmartQuotes uses backslash escapes instead of null-escapes
+                    text = re.sub(r'(?<=\x00)([-\\\'".`])', r'\\\1', str(txtnode))
+                else:
+                    text = txtnode.astext()
+
+                yield ('plain', text)
+            else:
+                # skip smart quotes
+                yield ('literal', txtnode.astext())
 
 
 class DoctreeReadEvent(SphinxTransform):

tests/test_markup.py

@@ -13,7 +13,6 @@ import re
 import pytest
 from docutils import frontend, utils, nodes
 from docutils.parsers.rst import Parser as RstParser
-from docutils.transforms.universal import SmartQuotes
 
 from sphinx import addnodes
 from sphinx.builders.html.transforms import KeyboardTransform
@@ -21,6 +20,8 @@ from sphinx.builders.latex import LaTeXBuilder
 from sphinx.builders.latex.theming import ThemeFactory
 from sphinx.roles import XRefRole
 from sphinx.testing.util import Struct, assert_node
+from sphinx.transforms import SphinxSmartQuotes
+from sphinx.util import docutils
 from sphinx.util import texescape
 from sphinx.util.docutils import sphinx_domains
 from sphinx.writers.html import HTMLWriter, HTMLTranslator
@@ -67,7 +68,7 @@ def parse(new_document):
         document = new_document()
         parser = RstParser()
         parser.parse(rst, document)
-        SmartQuotes(document, startnode=None).apply()
+        SphinxSmartQuotes(document, startnode=None).apply()
         for msg in document.traverse(nodes.system_message):
             if msg['level'] == 1:
                 msg.replace_self([])
@@ -349,6 +350,21 @@ def test_inline(get_verifier, type, rst, html_expected, latex_expected):
     verifier(rst, html_expected, latex_expected)
 
 
+@pytest.mark.parametrize('type,rst,html_expected,latex_expected', [
+    (
+        'verify',
+        r'4 backslashes \\\\',
+        r'<p>4 backslashes \\</p>',
+        None,
+    ),
+])
+@pytest.mark.skipif(docutils.__version_info__ < (0, 16),
+                    reason='docutils-0.16 or above is required')
+def test_inline_docutils16(get_verifier, type, rst, html_expected, latex_expected):
+    verifier = get_verifier(type)
+    verifier(rst, html_expected, latex_expected)
+
+
 @pytest.mark.sphinx(confoverrides={'latex_engine': 'xelatex'})
 @pytest.mark.parametrize('type,rst,html_expected,latex_expected', [
     (