Add compatibility for RTD addons

Author: daltzctr

sphinxext/opengraph/__init__.py

@@ -89,7 +89,13 @@ def get_tags(
         parse_result = urlparse(config["html_baseurl"])
 
         if config["html_baseurl"] is None:
-            raise OSError("ReadTheDocs did not provide a valid canonical URL!")
+            # rtd addons no longer configures html_baseurl
+            rtd_canonical_url = os.getenv("READTHEDOCS_CANONICAL_URL", "")
+
+            if not rtd_canonical_url:
+                raise OSError("ReadTheDocs did not provide a valid canonical URL!")
+            else:
+                parse_result = urlparse(rtd_canonical_url)
 
         # Grab root url from canonical url
         config["ogp_site_url"] = urlunparse(