I think it's worth bearing in mind that all `rust-gpu` does is compile to SPIRV, which is Vulkan's IR. So in a sense layers 2. and 3. are optional, or at least parallel layers rather than accumulative.

And it's also worth remembering that all of Rust's tooling can be used for building its shaders; `cargo`, `cargo test`, `cargo clippy`, `rust-analyzer` (Rust's LSP server).

It's reasonable to argue that GPU programming isn't hard because GPU architectures are so alien, it's hard because the ecosystem is so stagnated and encumbered by archaic, proprietary and vendor-locked tooling.

Layers 2 and 3 are implementation specific and you can do it however you wish. The point is that a rust program is running on your GPU, whatever GPU. That’s amazing!