Try out simple compute shader not work, while fragement works

[pipehappy]

Expected Behaviour

In the same place, replace simple fragment shader with compute shader. The compute shader one doesn't work.

Example & Steps To Reproduce

1. In the caller crate, I have line:

    const BLENDER_BLOCK: &[u8] = include_bytes!(env!("blender_block.spv"));
   

2. In the caller Cargo.toml:

    [build-dependencies]
    spirv-builder = { path = "../../rust-gpu/crates/spirv-builder", version = "0.9" }
   

3. In the caller build.rs

    use spirv_builder::{MetadataPrintout, SpirvBuilder};    
    fn main() -> Result<(), Box<dyn std::error::Error>> {
        SpirvBuilder::new("../shader_collection/blender_block", "spirv-unknown-vulkan1.3")
            .print_metadata(MetadataPrintout::Full)
            .build()?;  
        Ok(())
    }
   

4. In the shader crate, if it's fragement shader:

    #![cfg_attr(target_arch = "spirv", no_std)]
    use spirv_std::glam::{vec4, Vec4};
    
    #[spirv(fragment)]
    pub fn main_fs(output: &mut Vec4) {
        *output = vec4(1.0, 0.0, 0.0, 1.0);
   }
   

It works, but with compute shader:

    #![cfg_attr(target_arch = "spirv", no_std)]

    use spirv_std::spirv;
    use spirv_std::glam::{UVec3};

    #[spirv(compute(threads(16, 16)))]
    pub fn main_cs(
        #[spirv(global_invocation_id)] id: UVec3,
    ) {
        let _index = id.x as usize;
    }

It emit noentrypoint error:

       Compiling editor_driver v0.1.0 (/game/game_driver)
    error: failed to run custom build command for `editor_driver v0.1.0 (/game/game_driver)`
    
    Caused by:
      process didn't exit successfully: `/game/target/debug/build/game_driver-92bce6ae680a18bd/build-script-build` (exit status: 1)
      --- stdout
      cargo:rerun-if-env-changed=RUSTGPU_CODEGEN_ARGS
      cargo:rerun-if-env-changed=RUSTGPU_RUSTFLAGS
      cargo:rerun-if-env-changed=RUSTGPU_CARGOFLAGS
    
      --- stderr
         Compiling blender_block v0.1.0 (/game/game_driver_shader/blender_block)
      error: No OpEntryPoint instruction was found. This is only allowed if the Linkage capability is being used.
        |
       = note: module `/game/target/spirv-builder/spirv-unknown-vulkan1.3/release/deps/blender_block.spv`
    
      warning: an unknown error occurred
        |
        = note: spirv-opt failed, leaving as unoptimized
        = note: module `/game/target/spirv-builder/spirv-unknown-vulkan1.3/release/deps/blender_block.spv`
    
      error: error:0:0 - No OpEntryPoint instruction was found. This is only allowed if the Linkage capability is being used.
        |
        = note: spirv-val failed
        = note: module `/game/target/spirv-builder/spirv-unknown-vulkan1.3/release/deps/blender_block.spv`
    
      warning: `blender_block` (lib) generated 1 warning
      error: could not compile `blender_block` (lib) due to 2 previous errors; 1 warning emitted
      Error: BuildFailed

System Info

rustc -V
rustc 1.90.0-nightly (35f603652 2025-06-29)

spirv-val --version
SPIRV-Tools v2025.1 unknown hash, 2025-05-23T15:12:49+00:00
Targets:
  SPIR-V 1.0
  SPIR-V 1.1
  SPIR-V 1.2
  SPIR-V 1.3
  SPIR-V 1.4
  SPIR-V 1.5
  SPIR-V 1.6
  SPIR-V 1.2 (under OpenCL 2.2 Full Profile semantics)
  SPIR-V 1.0 (under Vulkan 1.0 semantics)
  SPIR-V 1.3 (under Vulkan 1.1 semantics)
  SPIR-V 1.4 (under Vulkan 1.1 semantics)
  SPIR-V 1.5 (under Vulkan 1.2 semantics)
  SPIR-V 1.6 (under Vulkan 1.3 semantics) SPIR-V 1.6 (under Vulkan 1.4 semantics)

[nazar-pc]

Maybe an edge-case due to dead-code elimination? Your shader is not doing anything at all, in contrast to fragment shader. Try a similar assignment.

[LegNeato]

#293

[nazar-pc]

I assumed that this one was in the root module (IIRC #[no_std] can't be used in submodules), but maybe it wasn't

[pipehappy]

Maybe an edge-case due to dead-code elimination? Your shader is not doing anything at all, in contrast to fragment shader. Try a similar assignment.

This is. Add something to it, make it compile. Yeah, It's the root module. Thx!