Support source built source artifacts

Author: arrdem

pip/private/extension.bzl

@@ -227,7 +227,9 @@ def _raw_sdist_repos(module_ctx, lock_specs):
                 if sdist == None:
                     continue
 
-                url = sdist["url"]
+                # Note that for source=url=... packages, the URL may not be
+                # repeated in the sdist spec so we have to replicate it down.
+                url = sdist.get("url", package["source"].get("url"))
                 shasum = sdist["hash"][len("sha256:"):]
 
                 # FIXME: Do we need to factor in the shasum or source her? Could