Don't fail when override is called from a non-root module

[mailto-jonas]

🐞 bug report

Affected Rule

The error is in pypi module extension when using the override tag class. See attached patch for location.

The issue is caused by the rule:

Non-root modules are failing to load.

Is this a regression?

This has never worked since the introduction of bzlmod.

Description

I have a Bazel module that I use in two different setup, where it in the first scenario acts as the root module and in the second scenario it is exported and used as a non-root module. The module is using rules_python and needs to apply a pip patch using the override tag class. However, in the current implementation, rules_python does not allow any calls to override when non-root, leading to a failure. Since there is no support for selects of if-cases within the MODULE.bazel file, this behavior prevents the second setup described above.

It would be beneficial if rules_python would trigger a warning instead of failing, to support the above use cases.

🔬 Minimal Reproduction

Add the following code to a non root module:
pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip")
pip.override()

🔥 Exception or Error

The module extension calls: fail("overrides are only supported in root modules")

🌍 Your Environment

Ubuntu 22.04
Bazel 8.0.0
rules_python 1.0.0
non_root_override.patch.txt