Expose more information on compiled entry points

[LoKolbasz]

Problem

Right now the entry_points in CompileResult contains names only. This limits limits our/the users ability to generate code.

Proposal

Exposing some additional information on them could help with generating code, without prior knowledge of how each entry point works (like having a dictionary of graphics and compute shaders).

Expose SpirV representation

Right now I am thinking of putting a version of the generated EntryPoint spirv lang struct into rustc_codegen_spirv_types because of how easy it is to implement.

pub struct EntryPoint {
    pub execution_model: spirv::ExecutionModel,
    pub entry_point: spirv::Word,
    pub name: String,
    pub interface: Vec<spirv::Word>,
}

Use naga

Another idea I had was using naga::ir::EntryPoint

pub struct EntryPoint {
    pub name: String,
    pub stage: ShaderStage,
    pub early_depth_test: Option<EarlyDepthTest>,
    pub workgroup_size: [u32; 3],
    pub workgroup_size_overrides: Option<[Option<Handle<Expression>>; 3]>,
    pub function: Function,
}

but this is a bit detached from the underlying spirv (harder to parse from spirv code + less shader stages etc)

Unique struct

The best version would probably be a combination of the 2.

Even if it doesn't end up getting merged, I'll do it for my own project. All insights are welcome.

[Firestar99]

Generally, I do agree that more information would be nice. But take note that spirv-builder and rustc_codegen_spirv run in different processes, so either we just serialize a lot more information through the json metadata (easier and potentially faster) or we need to have spirv-builder parse the resulting spirv again. I could also see a mixed approach, where we expose a function for you to call to parse the spirv using the spirv crate.

As a workaround, in my project I opted to have a custom proc macro wrapping all entry points generate me some extra symbols:
https://github.com/Firestar99/nanite-at-home/blob/9510b36ff7cd0f7eec96cbb8ba22dd3e88cc3fcf/rust-gpu-bindless/crates/macros/src/bindless.rs#L105-L108
And then have my build script generate code that references these symbols:
https://github.com/Firestar99/nanite-at-home/blob/main/rust-gpu-bindless/crates/shader-builder/src/codegen.rs#L42-L55