(joe) unsure why it's ok for find_all_candidates to fail sometimes but not others

Author: jbylund

src/pip/_internal/resolution/resolvelib/resolver.py

@@ -90,11 +90,15 @@ def resolve(
             reporter,
         )
 
+        def _maybe_find_candidates(req):
+            ident = provider.identify(req)
+            try:
+                self.factory._finder.find_all_candidates(ident)
+            except AttributeError:
+                pass
+
         with ThreadPool() as tp:
-            for _ in tp.imap_unordered(
-                self.factory._finder.find_all_candidates,
-                (provider.identify(r) for r in collected.requirements),
-            ):
+            for _ in tp.imap_unordered(_maybe_find_candidates, collected.requirements):
                 pass
 
         try: