debug: fail if we have a bug in the logic and try to use the same file for multiple platforms

Author: aignas

python/private/pypi/parse_requirements.bzl

@@ -332,7 +332,11 @@ def parse_requirements(
                 tokenized_options.append(p)
 
         pip_args = tokenized_options + extra_pip_args
+        logger.debug(lambda: "Using {} for {}".format(file, plats))
         for p in plats:
+            if p in requirements:
+                fail_fn("Attempting to override a requirements file. Existing value: {}".format(requirements[p]))
+                return None
             requirements[p] = requirements_dict
             options[p] = pip_args