only use python to eval requirements if there are markers

Author: aignas

python/private/pypi/parse_requirements.bzl

@@ -347,7 +347,8 @@ def parse_requirements(
                 {},
             )
 
-            reqs_with_env_markers.setdefault(requirement_line, []).append(target_platform)
+            if ";" in requirement_line:
+                reqs_with_env_markers.setdefault(requirement_line, []).append(target_platform)
 
             for_req = for_whl.setdefault(
                 (requirement_line, ",".join(extra_pip_args)),
@@ -364,6 +365,11 @@ def parse_requirements(
 
     # This may call to Python, so execute it early (before calling to the
     # internet below) and ensure that we call it only once.
+    #
+    # NOTE @aignas 2024-07-13: in the future, if this is something that we want
+    # to do, we could use Python to parse the requirement lines and infer the
+    # URL of the files to download things from. This should be important for
+    # VCS package references.
     env_marker_target_platforms = evaluate_markers(reqs_with_env_markers)
     if logger:
         logger.debug(lambda: "Evaluated env markers from:\n{}\n\nTo:\n{}".format(