[BUG] Build failes due to Bazel 7.0.0 breaking change

[rhaps0dy]

Describe the bug

When building in the default Docker env, the following error comes up

ERROR: /app/envpool/atari/BUILD:20:8: output 'envpool/atari/roms' of //envpool/atari:gen_atari_roms is a directory; dependency checking of directories is unsound
ERROR: /app/envpool/atari/BUILD:20:8: Executing genrule //envpool/atari:gen_atari_roms failed: not all outputs were created or valid

To Reproduce

1. Run make docker-dev
2. Inside the container run make bazel-debug

Expected behavior

The code builds

System info

I reproduced this bug:

• under Orbstack docker on Mac. which is a x86 VM
• in a x86_64 Ubuntu machine.

Reason and Possible fixes

I was able to work around this by setting export USE_BAZEL_VERSION=6.4.0. Then Bazelisk downloads and runs the appropriate Bazel version. I suggest adding that to the documentation.

Bazel 7.0.0 disables version checking for directories and symlinks, because it's unsound. (I gleaned this from this GitHub issue) Envpool has some genrules that output directories.

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have read the documentation (required)
• I have provided a minimal working example to reproduce the bug (required)

[Trinkle23897]

This should be fixed on main now.

The root cause here was real: Bazel 7+ got stricter about directory outputs, and EnvPool still had directory-producing build steps in a few places. We fixed that in #338:

• envpool/atari/BUILD now uses copy_to_directory(...) for gen_atari_roms instead of a directory-producing genrule.
• envpool/vizdoom/BUILD now declares explicit maps/*.cfg / maps/*.wad outputs instead of using a directory output.
• the default Bazel version in the repo is now 8.6.0 (Makefile / Dockerfiles were updated accordingly).

So this is no longer just a docs workaround like USE_BAZEL_VERSION=6.4.0; the BUILD files were updated to work with newer Bazel semantics.

If you pull current main, the original directory-output failure should be gone.