Build breakage with upcoming Bazel change for Python toolchains

[brandjon]

This project fails to build when --incompatible_use_python_toolchains is enabled. It looks like you have a Python 2 target used as a tool in the host configuration, but the host configuration by default uses Python 3. We don't support multiple Python versions in the host configuration, but you can choose which version is used build-wide by setting --host_force_python=PY2. See the migration bug and bazelbuild/bazel#6443 for details.

[davschm]

Thanks for making us aware of this. We have temporarily fixed it with --host_force_python=PY2 in
e028093.

The problem seems to be that pip_import and pip_install still download Python-2-compatible wheels of the dependencies even though the host configuration uses Python 3. Do you have any suggestion what to do about this?

[brandjon]

This will have to be fixed in rules_python. I can look into that after this toolchain flag flip is in. In the meantime --host_force_python is the way to go if you have PY2-only targets built in the host configuration.

I'm reopening this because this project is still failing in our downstream CI. Looking at one of the failures, I see here that the python_version attribute is not set (in the py_test created by ros_py_test). The default is PY3, so you may need to add python_version = "PY2" to the macro (or pass it in as a macro parameter if the required version differs between call sites).

[brandjon]

Er, I'm not reopening this because I forgot I'm posting in a repo I don't have commit rights to. Leaving that to you. =)

[drigz]

Thanks for the pointer, will look into why the previous commit didn't fix it!

[brandjon]

Confirmed fixed in most recent CI run. Thanks!