docs: Remove trailing slash from canonical URL for non-root docs.

The root pages for API, integrations and policies documentation
have a trailing slash for the canoncial URL, but the individual
articles on those pages do not have a trailing slash for the page
we want to mark as canonical.

zerver/tests/test_docs.py

@@ -251,6 +251,14 @@ class DocPageTest(ZulipTestCase):
         )
         self.assertEqual(result.status_code, 404)
 
+        result = self.client_get(
+            # Non-root API docs pages do not have a trailing slash.
+            "/api/changelog/",
+            follow=True,
+            HTTP_X_REQUESTED_WITH="XMLHttpRequest",
+        )
+        self.assertEqual(result.status_code, 404)
+
     def test_dev_environment_endpoints(self) -> None:
         self._test("/devlogin/", ["Normal users"])
         self._test("/devtools/", ["Useful development URLs"])

zerver/views/documentation.py

@@ -77,7 +77,12 @@ def add_api_url_context(
 
 
 def add_canonical_link_context(context: dict[str, Any], request: HttpRequest) -> None:
-    context["REL_CANONICAL_LINK"] = f"https://zulip.com{request.path}"
+    if request.path in ["/api/", "/policies/", "/integrations/"]:
+        # Root doc pages have a trailing slash in the canonical URL.
+        canonical_path = request.path
+    else:
+        canonical_path = request.path.removesuffix("/")
+    context["REL_CANONICAL_LINK"] = f"https://zulip.com{canonical_path}"
 
 
 class ApiURLView(TemplateView):