Redirects: fix root redirect (/ -> <anything>) (#11265)

The rstrip call was removing the whole path for `/`,
we need to preserve the leading `/` in the path.

readthedocs/proxito/tests/test_old_redirects.py

@@ -1243,6 +1243,51 @@ def test_redirect_with_301_status(self):
             "http://project.dev.readthedocs.io/en/latest/tutorial/install.html",
         )
 
+    def test_page_root_redirect(self):
+        fixture.get(
+            Redirect,
+            project=self.project,
+            redirect_type=PAGE_REDIRECT,
+            from_url="/",
+            to_url="https://example.com/",
+            force=True,
+        )
+        r = self.client.get(
+            "/en/latest/", headers={"host": "project.dev.readthedocs.io"}
+        )
+        self.assertEqual(r.status_code, 302)
+        self.assertEqual(r["Location"], "https://example.com/")
+
+    def test_exact_root_redirect_single_version(self):
+        self.project.versioning_scheme = SINGLE_VERSION_WITHOUT_TRANSLATIONS
+        self.project.save()
+        fixture.get(
+            Redirect,
+            project=self.project,
+            redirect_type=EXACT_REDIRECT,
+            from_url="/",
+            to_url="https://example.com/",
+            force=True,
+        )
+        r = self.client.get("/", headers={"host": "project.dev.readthedocs.io"})
+        self.assertEqual(r.status_code, 302)
+        self.assertEqual(r["Location"], "https://example.com/")
+
+    def test_page_root_redirect_single_version(self):
+        self.project.versioning_scheme = SINGLE_VERSION_WITHOUT_TRANSLATIONS
+        self.project.save()
+        fixture.get(
+            Redirect,
+            project=self.project,
+            redirect_type=PAGE_REDIRECT,
+            from_url="/",
+            to_url="https://example.com/",
+            force=True,
+        )
+        r = self.client.get("/", headers={"host": "project.dev.readthedocs.io"})
+        self.assertEqual(r.status_code, 302)
+        self.assertEqual(r["Location"], "https://example.com/")
+
 
 @override_settings(
     PYTHON_MEDIA=True,

readthedocs/redirects/querysets.py

@@ -60,8 +60,10 @@ def get_matching_redirect_with_path(
 
         # Useful to allow redirects to match paths with or without trailling slash.
         # For example, ``/docs`` will match ``/docs/`` and ``/docs``.
-        filename_without_trailling_slash = normalized_filename.rstrip("/")
-        path_without_trailling_slash = normalized_path.rstrip("/")
+        filename_without_trailling_slash = self._strip_trailling_slash(
+            normalized_filename
+        )
+        path_without_trailling_slash = self._strip_trailling_slash(normalized_path)
 
         # Add extra fields with the ``filename`` and ``path`` to perform a
         # filter at db level instead with Python.
@@ -154,3 +156,10 @@ def _normalize_path(self, path):
         normalized_path = parsed_path._replace(query="").geturl()
         normalized_path = "/" + normalized_path.lstrip("/")
         return normalized_path
+
+    def _strip_trailling_slash(self, path):
+        """Stripe the trailling slash from the path, making sure the root path is always ``/``."""
+        path = path.rstrip("/")
+        if path == "":
+            return "/"
+        return path