fix: remap dead hg.python.org release-notes URLs to GitHub equivalents

apps/downloads/models.py

@@ -114,6 +114,29 @@ def get_absolute_url(self):
             return self.release_page.get_absolute_url()
         return reverse("download:download_release_detail", kwargs={"release_slug": self.slug})
 
+    @property
+    def corrected_release_notes_url(self):
+        """Return the release notes URL, converting dead hg.python.org links to GitHub.
+
+        Old Mercurial-hosted URLs (hg.python.org) are no longer reachable.
+        This property remaps them to their equivalent paths on GitHub so that
+        the "Release notes" links on the downloads page still work for legacy
+        releases (3.3.6 and earlier).
+
+        Example::
+
+            http://hg.python.org/cpython/file/v3.3.6/Misc/NEWS
+            → https://github.com/python/cpython/blob/v3.3.6/Misc/NEWS
+        """
+        url = self.release_notes_url
+        if not url:
+            return url
+        match = re.match(r"https?://hg\.python\.org/cpython/file/([^/]+)/(.+)", url)
+        if match:
+            tag, path = match.group(1), match.group(2)
+            return f"https://github.com/python/cpython/blob/{tag}/{path}"
+        return url
+
     def download_file_for_os(self, os_slug):
         """Given an OS slug return the appropriate download file."""
         try:
@@ -430,3 +453,4 @@ class Meta:
                 violation_error_message="All file URLs must begin with 'https://www.python.org/'",
             ),
         ]
+

apps/downloads/templates/downloads/index.html

@@ -76,7 +76,7 @@ <h2 class="widget-title">Looking for a specific release?</h2>
                             <span class="release-number"><a href="{{ r.get_absolute_url }}">{{ r.name }}</a></span>
                             <span class="release-date">{{ r.release_date|date }}</span>
                             <span class="release-download"><a href="{{ r.get_absolute_url }}"><span aria-hidden="true" class="icon-download"></span> Download</a></span>
-                            <span class="release-enhancements"><a href="{{ r.release_notes_url }}">Release notes</a></span>
+                            <span class="release-enhancements">{% if r.corrected_release_notes_url %}<a href="{{ r.corrected_release_notes_url }}">Release notes</a>{% else %}Release notes{% endif %}</span>
                         </li>
                         {% endfor %}
                     </ol>
@@ -127,3 +127,4 @@ <h2 class="widget-title">Looking for a specific release?</h2>
                     {% box 'download-pgp' %}
                 </div>
 {% endblock content %}
+

apps/downloads/tests/test_models.py

@@ -311,3 +311,53 @@ def test_release_file_urls_not_python_dot_org(self):
                         name="Windows installer draft",
                         **kwargs,
                     )
+
+class ReleaseNotesURLTests(BaseDownloadTests):
+    """Tests for Release.corrected_release_notes_url property."""
+
+    def test_hg_url_converted_to_github(self):
+        """An hg.python.org URL is remapped to its GitHub equivalent."""
+        release = Release.objects.create(
+            version=Release.PYTHON3,
+            name="Python 3.3.6",
+            is_published=True,
+            release_notes_url="http://hg.python.org/cpython/file/v3.3.6/Misc/NEWS",
+        )
+        self.assertEqual(
+            release.corrected_release_notes_url,
+            "https://github.com/python/cpython/blob/v3.3.6/Misc/NEWS",
+        )
+
+    def test_https_hg_url_also_converted(self):
+        """An https hg.python.org URL is also remapped to GitHub."""
+        release = Release.objects.create(
+            version=Release.PYTHON3,
+            name="Python 3.2.6",
+            is_published=True,
+            release_notes_url="https://hg.python.org/cpython/file/v3.2.6/Misc/NEWS",
+        )
+        self.assertEqual(
+            release.corrected_release_notes_url,
+            "https://github.com/python/cpython/blob/v3.2.6/Misc/NEWS",
+        )
+
+    def test_modern_url_returned_unchanged(self):
+        """A non-hg URL (e.g. already on GitHub) is returned unchanged."""
+        url = "https://github.com/python/cpython/blob/v3.12.0/Misc/NEWS.d"
+        release = Release.objects.create(
+            version=Release.PYTHON3,
+            name="Python 3.12.0",
+            is_published=True,
+            release_notes_url=url,
+        )
+        self.assertEqual(release.corrected_release_notes_url, url)
+
+    def test_empty_url_returns_empty(self):
+        """An empty release_notes_url returns an empty string."""
+        release = Release.objects.create(
+            version=Release.PYTHON3,
+            name="Python 3.11.0",
+            is_published=True,
+            release_notes_url="",
+        )
+        self.assertEqual(release.corrected_release_notes_url, "")