Summary

imports runfiles handling of external projects appears to have broken with the switch to --legacy_external_runfiles=False in Bazel 8.0.0.

Minimal reproducer

https://github.com/armandomontanez/bazel_reproducers/tree/main/external_runfiles_broken_rules_python

Reproduces on both macOS and linux.

Additional notes

I haven't unwound yet whether or not all import handling of external py_* rules are completely broken, I noticed this specifically with py_proto_library rules that use strip_import_prefix and live in an external repository.

I noticed this when working with nanopb where sys.path reported the import path as:

/private/var/tmp/_bazel_amontanez/e724b21efc8bc19866072fbc72ee5907/sandbox/darwin-sandbox/7/execroot/_main/bazel-out/darwin_x86_64-opt-exec-ST-e8d06b237d06/bin/external/nanopb+/protoc-gen-nanopb.runfiles/_main/external/nanopb+/_virtual_imports/nanopb_proto

when the files actually existed at:

/private/var/tmp/_bazel_amontanez/e724b21efc8bc19866072fbc72ee5907/sandbox/darwin-sandbox/7/execroot/_main/bazel-out/darwin_x86_64-opt-exec-ST-e8d06b237d06/bin/external/nanopb+/protoc-gen-nanopb.runfiles/_main/../nanopb+/_virtual_imports/nanopb_proto