Use rules_python python_bootstrap_template instead of bazel_tools's

[rickeylev]

When a py_binary is built, the resulting executable is expanded from the template python_bootstrap_template.txt.

As of Bazel 7, py_runtime allows specifying this template. This allows us to customize program startup without changes in Bazel itself.

I copied the one in Bazel into rules_python, it lives here: https://github.com/bazelbuild/rules_python/blob/main/python/private/python_bootstrap_template.txt#L4

The basic todos are:

• Change toolchain generation code, the part that creates py_runtime(), and add a version check for Bazel 7. If its Bazel 7, set bootstrap_template to the rules python template.

The benefits of this are:

1. We can now have python version specific bootstrap templates. Or other platform-specific templates.
2. We can use some shell tricks to help solve py_binary with hermetic toolchain requires a system interpreter #691. I'm not sure we can entirely solve it, but we probably get close enough.

[groodt]

The will be huge! Can’t wait. So many things can be improved if the rules can manage the bootstrap.

[armandomontanez]

Is this issue resolved? While debugging some Python stuff, I found the bootstrap template from rules_python was being used.

[rickeylev]

Yeah, I think so. The py_runtime implementation was switch over to starlark, and it gets its bootstrap from rules_python, which is used by py_binary.

For Bazel 6, we have to keep the template compatible across all python versions. With Bazel 7 we could (but don't currently) create a bootstrap for each specific version.

But yes, for the most part, rules_python does control it directly now.

[github-actions]

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[arrdem]

🎉