Handle overlapping raw HTML matches (#770)

Recursively run substitution to handle overlapping matches.
Fixes #458.

Author: PhilipTrauner

docs/change_log/release-3.1.md

@@ -31,6 +31,7 @@ The following new features have been included in the release:
 
 The following bug fixes are included in the 3.1 release:
 
+* Overlapping raw HTML matches no longer leave placeholders behind (#458).
 * Emphasis patterns now recognize newline characters as whitespace (#783).
 * Version format had been updated to be PEP 440 compliant (#736).
 * Block level elements are defined per instance, not as class attributes

markdown/postprocessors.py

@@ -81,9 +81,14 @@ def run(self, text):
 
         if replacements:
             pattern = re.compile("|".join(re.escape(k) for k in replacements))
-            text = pattern.sub(lambda m: replacements[m.group(0)], text)
-
-        return text
+            processed_text = pattern.sub(lambda m: replacements[m.group(0)], text)
+        else:
+            return text
+
+        if processed_text == text:
+            return processed_text
+        else:
+            return self.run(processed_text)
 
     def isblocklevel(self, html):
         m = re.match(r'^\<\/?([^ >]+)', html)

tests/test_syntax/extensions/test_fenced_code.py

@@ -0,0 +1,53 @@
+# -*- coding: utf-8 -*-
+"""
+Python Markdown
+
+A Python implementation of John Gruber's Markdown.
+
+Documentation: https://python-markdown.github.io/
+GitHub: https://github.com/Python-Markdown/markdown/
+PyPI: https://pypi.org/project/Markdown/
+
+Started by Manfred Stienstra (http://www.dwerg.net/).
+Maintained for a few years by Yuri Takhteyev (http://www.freewisdom.org).
+Currently maintained by Waylan Limberg (https://github.com/waylan),
+Dmitry Shachnev (https://github.com/mitya57) and Isaac Muse (https://github.com/facelessuser).
+
+Copyright 2007-2018 The Python Markdown Project (v. 1.7 and later)
+Copyright 2004, 2005, 2006 Yuri Takhteyev (v. 0.2-1.6b)
+Copyright 2004 Manfred Stienstra (the original version)
+
+License: BSD (see LICENSE.md for details).
+"""
+
+from __future__ import unicode_literals
+from markdown.test_tools import TestCase
+
+
+class TestFencedCode(TestCase):
+
+    # TODO: Move the rest of the fenced code tests here.
+
+    def test_fenced_code_in_raw_html(self):
+        self.assertMarkdownRenders(
+            self.dedent(
+                """
+                <details>
+                ```
+                Begone placeholders!
+                ```
+                </details>
+                """
+            ),
+            self.dedent(
+                """
+                <details>
+
+                <pre><code>Begone placeholders!
+                </code></pre>
+
+                </details>
+                """
+            ),
+            extensions=['fenced_code']
+        )