Using bzlmod (at all) breaks Python interpreter version specifications

[tervay-bdai]

🐞 bug report

Affected Rule

The issue is caused by the rule: Specific version-related `py_binary`

Is this a regression?

No, does not work as far back as 0.18.0, and repro does not work on 0.17.0.

Description

Enabling the --experimental_enable_bzlmod flag (even with an empty MODULE.bazel) causes Bazel to use the system Python interpreter, not the one specified in WORKSPACE.

🔬 Minimal Reproduction

https://github.com/tervay-bdai/pyexample

This has a Python 3.9 toolchain set up in WORKSPACE. My system interpreter is 3.10.6. The bazelmod enable flag can be enabled with --config=bzlmod if you want. You should see two different versions (assuming your system interpreter is not 3.9).

🔥 Exception or Error

  
13:02 | ~/workspace/rpv | $ bazel run //src:main
INFO: Analyzed target //src:main (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //src:main up-to-date:
  bazel-bin/src/_main
INFO: Elapsed time: 0.203s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/src/main
3.9.16

13:02 | ~/workspace/rpv | $ bazel run //src:main --config=bzlmod
INFO: Analyzed target //src:main (66 packages loaded, 515 targets configured).
INFO: Found 1 target...
Target //src:main up-to-date:
  bazel-bin/src/_main
INFO: Elapsed time: 2.131s, Critical Path: 0.00s
INFO: 7 processes: 7 internal.
INFO: Build completed successfully, 7 total actions
INFO: Running command line: bazel-bin/src/main
3.10.6
  

🌍 Your Environment

Operating System:

  
14:30 | ~/workspace/rpv | $ uname -a
Linux jtervay-LT 5.19.0-46-generic #47~22.04.1-Ubuntu SMP PREEMPT_DYNAMIC Wed Jun 21 15:35:31 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
  

Output of bazel version:

  
14:30 | ~/workspace/rpv | $ bazel version
Bazelisk version: v1.16.0
Build label: 6.2.1
Build target: bazel-out/k8-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar
Build time: Fri Jun 2 16:59:58 2023 (1685725198)
Build timestamp: 1685725198
Build timestamp as int: 1685725198
  

Rules_python version:

  
0.24.0
  

[tervay-bdai]

This seems to be similar to bazelbuild/bazel#17289, but different, since the suggested fix (adding bazel_dep(name = "platforms", version = "0.0.5")) does not fix this one.

[chrislovecnm]

Enabling the --experimental_enable_bzlmod flag (even with an empty MODULE.bazel) causes Bazel to use the system Python interpreter, not the one specified in WORKSPACE.

So with bzlmod the configurations in the workspace file are not used. You need bzlmod configurations in the MODULE.bazel file, and also have an empty WORKSPACE.bzlmod file.

You can use WORKSPACE like configurations in the WORKSPACE.bzlmod file. But it is better to use the bzlmod configuration.

[tervay-bdai]

Seems this is intentional:

rules_python/python/repositories.bzl

Lines 502 to 504 in 5416257

	if BZLMOD_ENABLED:
	# you cannot used native.register_toolchains when using bzlmod.
	register_toolchains = False

Closing.