From 873b2ad5b1b6ef3c6ed808a47ad6ac579ff574fa Mon Sep 17 00:00:00 2001
From: chuenchen309 <48723787+chuenchen309@users.noreply.github.com>
Date: Mon, 20 Jul 2026 03:53:40 +0800
Subject: [PATCH] Lengthen the pre code fence so backtick runs can't close it
 early

`convert_pre` emitted a fixed three-backtick fence, so a `<pre>` whose content
contains a ``` run (or longer) produced an ambiguous fenced block that reparses
to different HTML: `<pre>foo\n```\nbar</pre>` closed the fence at the inner
```, splitting one code block into a code block, a paragraph, and an empty code
block.

Compute the fence from the longest backtick run in the content (at least three,
matching the previous default), the same mechanism `convert_code` already uses
for inline code. Per CommonMark section 4.5 the closing fence must have at
least as many backticks as the opening.
---
 markdownify/__init__.py   | 8 +++++++-
 tests/test_conversions.py | 9 +++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/markdownify/__init__.py b/markdownify/__init__.py
index 28cdaf6..99b3c63 100644
--- a/markdownify/__init__.py
+++ b/markdownify/__init__.py
@@ -702,7 +702,13 @@ def convert_pre(self, el, text, parent_tags):
         else:
             raise ValueError('Invalid value for strip_pre: %s' % self.options['strip_pre'])
 
-        return '\n\n```%s\n%s\n```\n\n' % (code_language, text)
+        # Use a fence long enough that no backtick run inside the code can close
+        # it early (CommonMark section 4.5: the closing fence must have at least
+        # as many backticks as the opening).
+        max_backticks = max((len(match) for match in re.findall(re_backtick_runs, text)), default=0)
+        fence = '`' * max(3, max_backticks + 1)
+
+        return '\n\n%s%s\n%s\n%s\n\n' % (fence, code_language, text, fence)
 
     def convert_q(self, el, text, parent_tags):
         return '"' + text + '"'
diff --git a/tests/test_conversions.py b/tests/test_conversions.py
index c95483c..0d74845 100644
--- a/tests/test_conversions.py
+++ b/tests/test_conversions.py
@@ -311,6 +311,15 @@ def test_pre():
     assert md("<p>foo</p>\n<pre>bar</pre>\n</p>baz</p>", sub_symbol="^") == "\n\nfoo\n\n```\nbar\n```\n\nbaz"
 
 
+def test_pre_backticks():
+    # A backtick run inside the code must not close the fence early: the fence
+    # needs at least one more backtick than the longest run in the content.
+    assert md('<pre>foo\n```\nbar</pre>') == '\n\n````\nfoo\n```\nbar\n````\n\n'
+    assert md('<pre><code>```</code></pre>') == '\n\n````\n```\n````\n\n'
+    assert md('<pre>a````b</pre>') == '\n\n`````\na````b\n`````\n\n'
+    assert md('<pre>plain</pre>') == '\n\n```\nplain\n```\n\n'
+
+
 def test_q():
     assert md('foo <q>quote</q> bar') == 'foo "quote" bar'
     assert md('foo <q cite="https://example.com">quote</q> bar') == 'foo "quote" bar'