Support (restrictive) load in MODULE.bazel

[joca-bt]

Description of the feature request:

Currently, the MODULE.bazel file must contain everything needed by the project within it, and cannot call load statements to help make it easier to navigate.

One situation in which it would be helpful to use load is when configuring external package managers, e.g. like with rules_jvm_external. On a Java project it is not unusual to depend on several external jars. Putting that configuration in MODULE.bazel can be considered as polluting the file and makes it more difficult to maintain.

This was originally opened in bazel-contrib/rules_jvm_external#854 and that issue provides further details on a specific example with rules_jvm_external.

Having the ability to use load to load constants or macros from other files would help us maintain a more organized MODULE.bazel.

What underlying problem are you trying to solve with this feature?

No response

Which operating system are you running Bazel on?

Linux

What is the output of bazel info release?

6.0.0

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

No response

Any other information, logs, or outputs that you want to share?

No response

[fmeum]

I don't think I'm exaggerating that much with the following claim: The availability of and reliance on load in WORKSPACE was a major contributor to its subpar performance.

Module extensions can accept label attributes on their tags and collect dependency information from the files pointed to by these labels. Without any changes to Bazel itself, rules_jvm_external could allow for the following usage where artifacts.json is some other file in your repo with e.g. an array of Maven coordinates:

maven = use_extension("@rules_jvm_external//:extensions.bzl", "maven")
maven.install(artifacts = "//:artifacts.json")

This would keep your MODULE.bazel file clean and your external Java dependencies separated from all the others while still allowing for fast discovery of the entire dependency tree.

[Wyverald]

What @fmeum said; although, we might explore allowing load from the current repository for the root module only, to better support large monorepos that will never be used as a dependency.

[shs96c]

Would there be an option of using load in a local repository, but when we upload to something like the BCR, having the load statements inlined so there's just the single MODULE.bazel file without any external dependencies?