Why don't other rules use _allowlist_function_transition

[UebelAndre]

Or more specifically, do the other rules support transitions?

Semi-related to #276 since I'm interested in cross-compilation.

[UebelAndre]

cc @hlopko

[hlopko]

All the rules work under transitions. What is special about rust_wasm_bindgen is that the rule itself performs the transition when analyzing wasm_file attribute (the target passed as this attribute will be built with a different configuration than the rust_wasm_bindgen). Transitions are quite a special hammer that is rarely needed. And we currently don't need it for the core Rust rules.

Configuration transitions have the potential to explode Bazel memory, cpu, and execution times if used incorrectly. _allowlist_function_transition is a way to limit usage of the transition when you want to be careful. If the rule doesn't use a transition this attribute is useless.

But yeah when the need arises, we can use transitions with core Rust rules just fine.