i was working on something else and realized a really nice way to auto-generate union rules leveraging the existing

enum

work, which led to an attempt at

VariantRule

in https://github.com/pantsbuild/pants/pull/8046 which makes

native_toolchain.py

, imho, much much easier to read. please let me know if this interface (adding

given=[...]

to the

@rule

constructor with any enum instances to specialize on) seems good, or if it could be improved!