WORKSPACE to MODULE.bazel migration setting default python version

[gfrankliu]

We are migrating from WORKSPACE to MODULE.bazel. Most of modules are now in MODULE.bazel and very few are still in WORKSPACE.

We have rules_python still in WORKSPACE because some of our internal custom python codes/rules/builds still need more time to update.

We use python version 3.10, eg: in WORKSPACE:

python_register_toolchains(
    name = "python_interpreter",
    python_version = "3.10",
)

We notice an issue where our external dependencies from MODULE.bazel are using python 3.11 instead of our default 3.10.

Since we are still using WORKSPACE and can't set python.toolchain(is_default = True, python_version = "3.10") in our root MODULE.bazel, how can we "tell" those external modules (they are already using MODULE.bazel) to use python 3.10?

[gfrankliu]

We are using rules_python 0.40.0, and latest bazel 7: bazel 7.4.1

[aignas]

That might be working as intended - MODULE.bazel dependencies are using the default toolchain set by bzlmod code and it cannot know anything about the WORKSPACE paths.

I am not sure if this is something that can be easily fixed.

At the same time, I am not sure why you can define your toolchain in bzlmod? You should still be able to use pip_parse from WORKSPACE with the toolchain set in MODULE.bazel.

[gfrankliu]

Thanks for the suggestion! I just tried this:

In MODULE.bazel, I added:

bazel_dep(name = "rules_python", version = "0.40.0")
python = use_extension("@rules_python//python/extensions:python.bzl", "python")
python.toolchain(is_default = True, python_version = "3.10")
use_repo(python, "python_3_10")

In WORKSPACE, I only have below lines, nothing else:

load("@rules_python//python:pip.bzl", "pip_parse")
pip_parse(
    name = "third_party_lib",
    requirements_lock = "//:requirements.txt",
)

bazel build gives this error:

ERROR: Failed to load Starlark extension '@@rules_python_internal//:rules_python_config.bzl'.
Cycle in the workspace file detected. This indicates that a repository is used prior to being defined.
The following chain of repository dependencies lead to the missing definition.
 - @@rules_python_internal
This could either mean you have to add the '@@rules_python_internal' repository with a statement like `http_archive` in your WORKSPACE file (note that transitive dependencies are not added automatically), or move an existing definition earlier in your WORKSPACE file.
ERROR: Error computing the main repository mapping: cycles detected during computation of main repo mapping

Since pip.parse isn't 100% matching pip_parse, it breaks some of our internal custom bazel rules. It will take some time for us to update all those custom rules. In the meantime, we would like to migrate non python stuff into MODULE.bazel.