`python_register_toolchains` does not select appropriate interpreter for target platform

[nvachhar]

🐞 bug report

Affected Rule

The issue is caused by the rule: python_register_toolchains

Is this a regression?

No

Description

python_register_toolchains registers the toolchains with exec_compatible_with but should register the toolchains with target_compatible_with instead according to the design here: https://github.com/bazelbuild/rules_python/blob/main/proposals/2019-02-12-design-for-a-python-toolchain.md

The result is cross-platform builds end up with an exec platform platform interpreter in the runfiles tree instead of a target platform interpeter.

🔬 Minimal Reproduction

From a checkout of https://github.com/nvachhar/rules_python_bug:

🔥 Exception or Error

Building for macos-x86_64 on a macos-x86_64 host results in an x86_64 interpeter.

$ bazel build --platforms :macos-x86_64 hello
INFO: Build option --platforms has changed, discarding analysis cache.
INFO: Analyzed target //:hello (0 packages loaded, 3974 targets configured).
INFO: Found 1 target...
Target //:hello up-to-date:
  bazel-bin/hello
INFO: Elapsed time: 0.352s, Critical Path: 0.03s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
$ ls bazel-bin/hello.runfiles                
MANIFEST*  __init__.py*  __main__/  python3_9_x86_64-apple-darwin/

Building for macos-arm64 on a macos-x86_64 host still results in an x86_64 interpeter.

$ bazel build --platforms :macos-arm64 hello 
INFO: Build option --platforms has changed, discarding analysis cache.
INFO: Analyzed target //:hello (0 packages loaded, 3974 targets configured).
INFO: Found 1 target...
Target //:hello up-to-date:
  bazel-bin/hello
INFO: Elapsed time: 0.387s, Critical Path: 0.03s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
$ ls bazel-bin/hello.runfiles               
MANIFEST*  __init__.py*  __main__/  python3_9_x86_64-apple-darwin/

🌍 Your Environment

Operating System:

  
macOS 12.3.1
  

Output of bazel version:

  
Bazelisk version: development
Build label: 5.0.0
Build target: bazel-out/darwin-opt/bin/src/main/java/com/google/devtools/build/lib/bazel/BazelServer_deploy.jar
Build time: Wed Jan 19 14:15:55 2022 (1642601755)
Build timestamp: 1642601755
Build timestamp as int: 1642601755
  

Rules_python version:

  
0.8.1
  

[jesseschalken]

Note the same problem was fixed in the Java toolchains in this commit: bazelbuild/bazel@d5559c1

[thundergolfer]

Thanks for the issue report. I can make the PR fix.

cc @f0rmiga

[UebelAndre]

@thundergolfer any updates here?

[groodt]

Fixed by #747