OutputTrianglesEXT Execution Mode not found (Mesh Shader)

[jre0]

I'm trying to make a mesh shader but some validation stage appears to incorrectly kick back with [OutputTrianglesEXT Execution Mode](error: [VUID-PrimitiveTriangleIndicesEXT-PrimitiveTriangleIndicesEXT-07054] The PrimitiveTriangleIndicesEXT decoration must be used with the OutputTrianglesEXT Execution Mode.) I do include OutputTrianglesEXT so this error appears to be a mistake.
Is it still possible to use the installed spirv tools instead of the rust crate? If so, the documentation appears out of date because I tried to use cargo run --features use-installed-tools and it says command not found. If I can use the installed tools, I might be able to avoid this error. I appreciate any help, including hints on where to start if I have to fix the bug myself.

Expected Behaviour

Because I use output_triangles_ext, I expect primitive_triangle_indices_ext to be available.

Example & Steps To Reproduce

Here is the shader code. It compiles because I commented out the lines that set the vertex indices. If you add them, it produces the error about requiring OutputTrianglesEXT. I used spirv tools spirv-dis to inspect the output and OutputTrianglesEXT is there.

#![no_std]
#![allow(unexpected_cfgs)]

use glam::*;
use spirv_std::arch::{emit_mesh_tasks_ext, set_mesh_outputs_ext};
use spirv_std::spirv;

#[spirv(mesh_ext(
    threads(1),
    output_vertices = 3,
    output_primitives_ext = 1,
    output_triangles_ext,
))]
pub fn mesh(
    #[spirv(position)] positions: &mut [Vec4; 3],
    // #[spirv(primitive_triangle_indices_ext)] indices: &mut [UVec3; 1],
) {
    unsafe {
        set_mesh_outputs_ext(3, 1);
    }
    positions[0] = Vec4::default();
    positions[1] = Vec4::default();
    // indices[0] = UVec3::new(0, 1, 2);
}

System Info

• Rust: rustc 1.89.0-nightly (be19eda0d 2025-06-22)
• OS: Kubuntu 24.04, kernel 6.8.0-79-generic (64-bit)
• GPU: NVIDIA GeForce GTX 1660 Ti/PCIe/SSE2
• SPIR-V: SPIRV-Tools v2025.3 v2025.3.rc1-0-g33e02568

Spirv and Backtrace

Spirv dis

; SPIR-V
; Version: 1.6
; Generator: Google rspirv; 0
; Bound: 190
; Schema: 0
               OpCapability Shader
               OpCapability MeshShadingEXT
               OpCapability VulkanMemoryModel
               OpExtension "SPV_EXT_mesh_shader"
               OpMemoryModel Logical Vulkan
               OpEntryPoint TaskEXT %1 "task"
               OpEntryPoint MeshEXT %2 "mesh" %3 %4 %5 %gl_Position
               OpEntryPoint Fragment %7 "fragment" %8
               OpExecutionMode %1 LocalSize 1 1 1
               OpExecutionMode %2 LocalSize 1 1 1
               OpExecutionMode %2 OutputVertices 3
               OpExecutionMode %2 OutputPrimitivesEXT 1
               OpExecutionMode %2 OutputTrianglesEXT
               OpExecutionMode %7 OriginUpperLeft
               OpMemberDecorate %_struct_16 0 Offset 0
               OpMemberDecorate %_struct_16 1 Offset 16
               OpMemberDecorate %_struct_16 2 Offset 32
               OpMemberDecorate %_struct_16 3 Offset 48
               OpMemberDecorate %_struct_17 0 Offset 0
               OpMemberDecorate %_struct_17 1 Offset 64
               OpDecorate %_struct_19 Block
               OpMemberDecorate %_struct_19 0 Offset 0
               OpDecorate %_runtimearr_v2float ArrayStride 8
               OpDecorate %_struct_21 Block
               OpMemberDecorate %_struct_21 0 Offset 0
               OpDecorate %_arr_v4float_uint_3 ArrayStride 16
               OpDecorate %3 Binding 0
               OpDecorate %3 DescriptorSet 0
               OpDecorate %4 NonWritable
               OpDecorate %4 Binding 1
               OpDecorate %4 DescriptorSet 0
               OpDecorate %5 NonWritable
               OpDecorate %5 Binding 2
               OpDecorate %5 DescriptorSet 0
               OpDecorate %gl_Position BuiltIn Position
               OpDecorate %8 Location 0
       %void = OpTypeVoid
         %24 = OpTypeFunction %void
       %uint = OpTypeInt 32 0
     %uint_1 = OpConstant %uint 1
      %float = OpTypeFloat 32
    %v4float = OpTypeVector %float 4
 %_struct_16 = OpTypeStruct %v4float %v4float %v4float %v4float
 %_struct_17 = OpTypeStruct %_struct_16 %_struct_16
 %_struct_19 = OpTypeStruct %_struct_17
%_ptr_Uniform__struct_19 = OpTypePointer Uniform %_struct_19
    %v2float = OpTypeVector %float 2
%_runtimearr_v2float = OpTypeRuntimeArray %v2float
 %_struct_21 = OpTypeStruct %_runtimearr_v2float
%_ptr_StorageBuffer__struct_21 = OpTypePointer StorageBuffer %_struct_21
     %uint_3 = OpConstant %uint 3
%_arr_v4float_uint_3 = OpTypeArray %v4float %uint_3
%_ptr_Output__arr_v4float_uint_3 = OpTypePointer Output %_arr_v4float_uint_3
          %3 = OpVariable %_ptr_Uniform__struct_19 Uniform
     %uint_0 = OpConstant %uint 0
          %4 = OpVariable %_ptr_StorageBuffer__struct_21 StorageBuffer
          %5 = OpVariable %_ptr_StorageBuffer__struct_21 StorageBuffer
%_ptr_Uniform__struct_16 = OpTypePointer Uniform %_struct_16
       %bool = OpTypeBool
%_ptr_StorageBuffer_v2float = OpTypePointer StorageBuffer %v2float
    %float_1 = OpConstant %float 1
         %41 = OpConstantComposite %v4float %float_1 %float_1 %float_1 %float_1
%_ptr_Output_v4float = OpTypePointer Output %v4float
%gl_Position = OpVariable %_ptr_Output__arr_v4float_uint_3 Output
          %8 = OpVariable %_ptr_Output_v4float Output
          %1 = OpFunction %void None %24
         %43 = OpLabel
               OpEmitMeshTasksEXT %uint_1 %uint_1 %uint_1
               OpFunctionEnd
          %2 = OpFunction %void None %24
         %46 = OpLabel
               OpSelectionMerge %188 None
               OpSwitch %uint_0 %189
        %189 = OpLabel
         %49 = OpArrayLength %uint %4 0
         %51 = OpArrayLength %uint %5 0
               OpSetMeshOutputsEXT %uint_3 %uint_1
         %52 = OpInBoundsAccessChain %_ptr_Uniform__struct_16 %3 %uint_0 %uint_0
         %53 = OpLoad %_struct_16 %52
         %54 = OpULessThan %bool %uint_0 %49
               OpSelectionMerge %56 None
               OpBranchConditional %54 %56 %57
         %56 = OpLabel
         %58 = OpInBoundsAccessChain %_ptr_StorageBuffer_v2float %4 %uint_0 %uint_0
         %59 = OpLoad %v2float %58
         %60 = OpCompositeExtract %float %59 0
         %61 = OpCompositeExtract %float %59 1
         %64 = OpCompositeExtract %v4float %53 0
         %65 = OpCompositeExtract %float %64 0
         %66 = OpFMul %float %65 %60
         %67 = OpCompositeExtract %float %64 1
         %68 = OpFMul %float %67 %60
         %69 = OpCompositeExtract %float %64 2
         %70 = OpFMul %float %69 %60
         %71 = OpCompositeExtract %float %64 3
         %72 = OpFMul %float %71 %60
         %73 = OpCompositeExtract %v4float %53 1
         %74 = OpCompositeExtract %float %73 0
         %75 = OpFMul %float %74 %61
         %76 = OpCompositeExtract %float %73 1
         %77 = OpFMul %float %76 %61
         %78 = OpCompositeExtract %float %73 2
         %79 = OpFMul %float %78 %61
         %80 = OpCompositeExtract %float %73 3
         %81 = OpFMul %float %80 %61
         %82 = OpFAdd %float %66 %75
         %83 = OpFAdd %float %68 %77
         %84 = OpFAdd %float %70 %79
         %85 = OpFAdd %float %72 %81
         %86 = OpCompositeExtract %v4float %53 2
         %87 = OpCompositeExtract %float %86 0
         %89 = OpCompositeExtract %float %86 1
         %91 = OpCompositeExtract %float %86 2
         %93 = OpCompositeExtract %float %86 3
         %95 = OpFAdd %float %82 %87
         %96 = OpFAdd %float %83 %89
         %97 = OpFAdd %float %84 %91
         %98 = OpFAdd %float %85 %93
         %99 = OpCompositeExtract %v4float %53 3
        %100 = OpCompositeExtract %float %99 0
        %102 = OpCompositeExtract %float %99 1
        %104 = OpCompositeExtract %float %99 2
        %106 = OpCompositeExtract %float %99 3
        %108 = OpFAdd %float %95 %100
        %109 = OpFAdd %float %96 %102
        %110 = OpFAdd %float %97 %104
        %111 = OpFAdd %float %98 %106
        %112 = OpCompositeConstruct %v4float %108 %109 %110 %111
        %113 = OpInBoundsAccessChain %_ptr_Output_v4float %gl_Position %uint_0
               OpStore %113 %112
               OpSelectionMerge %118 None
               OpBranchConditional %54 %118 %119
         %57 = OpLabel
               OpBranch %188
        %118 = OpLabel
        %122 = OpULessThan %bool %uint_1 %51
               OpSelectionMerge %124 None
               OpBranchConditional %122 %124 %125
        %119 = OpLabel
               OpBranch %188
        %124 = OpLabel
        %126 = OpInBoundsAccessChain %_ptr_StorageBuffer_v2float %5 %uint_0 %uint_1
        %127 = OpLoad %v2float %126
        %129 = OpCompositeExtract %float %127 0
        %130 = OpFAdd %float %60 %129
        %132 = OpCompositeExtract %float %127 1
        %133 = OpFAdd %float %61 %132
        %138 = OpFMul %float %65 %130
        %140 = OpFMul %float %67 %130
        %142 = OpFMul %float %69 %130
        %144 = OpFMul %float %71 %130
        %147 = OpFMul %float %74 %133
        %149 = OpFMul %float %76 %133
        %151 = OpFMul %float %78 %133
        %153 = OpFMul %float %80 %133
        %154 = OpFAdd %float %138 %147
        %155 = OpFAdd %float %140 %149
        %156 = OpFAdd %float %142 %151
        %157 = OpFAdd %float %144 %153
        %167 = OpFAdd %float %154 %87
        %168 = OpFAdd %float %155 %89
        %169 = OpFAdd %float %156 %91
        %170 = OpFAdd %float %157 %93
        %180 = OpFAdd %float %167 %100
        %181 = OpFAdd %float %168 %102
        %182 = OpFAdd %float %169 %104
        %183 = OpFAdd %float %170 %106
        %184 = OpCompositeConstruct %v4float %180 %181 %182 %183
        %185 = OpInBoundsAccessChain %_ptr_Output_v4float %gl_Position %uint_1
               OpStore %185 %184
               OpBranch %188
        %125 = OpLabel
               OpBranch %188
        %188 = OpLabel
               OpReturn
               OpFunctionEnd
          %7 = OpFunction %void None %24
        %186 = OpLabel
               OpStore %8 %41
               OpReturn
               OpFunctionEnd

Backtrace

cargo run
   Compiling line v0.1.0 (/home/julian/lapis/onyx/shader/line)
   Compiling onyx v0.1.0 (/home/julian/lapis/onyx)
error: failed to run custom build command for `onyx v0.1.0 (/home/julian/lapis/onyx)`

Caused by:
  process didn't exit successfully: `/home/julian/lapis/target/debug/build/onyx-df1ad9db8f2d015b/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 line v0.1.0 (/home/julian/lapis/onyx/shader/line)
  error: [VUID-PrimitiveTriangleIndicesEXT-PrimitiveTriangleIndicesEXT-07054] The PrimitiveTriangleIndicesEXT decoration must be used with the OutputTrianglesEXT Execution Mode. 
    |
    = note: module `/home/julian/lapis/target/spirv-builder/spirv-unknown-vulkan1.4/release/deps/line.spv`

  warning: an unknown error occurred
    |
    = note: spirv-opt failed, leaving as unoptimized
    = note: module `/home/julian/lapis/target/spirv-builder/spirv-unknown-vulkan1.4/release/deps/line.spv`

  error: error:0:0 - [VUID-PrimitiveTriangleIndicesEXT-PrimitiveTriangleIndicesEXT-07054] The PrimitiveTriangleIndicesEXT decoration must be used with the OutputTrianglesEXT Execution Mode. 
           %indices = OpVariable %_ptr_Output__arr_v3uint_uint_1 Output
    |
    = note: spirv-val failed
    = note: module `/home/julian/lapis/target/spirv-builder/spirv-unknown-vulkan1.4/release/deps/line.spv`

  warning: `line` (lib) generated 1 warning
  error: could not compile `line` (lib) due to 2 previous errors; 1 warning emitted
  Error: BuildFailed

[Firestar99]

Some working examples:

• from our compiletest for mesh shader emitting triangles: https://github.com/Rust-GPU/rust-gpu/blob/main/tests/compiletests/ui/arch/mesh_shader_output_triangles.rs
• from my project exclusively using mesh shaders: https://github.com/Firestar99/nanite-at-home/blob/main/space-engine-shader/src/renderer/meshlet/mesh_shader.rs

Otherwise, I could not repo this with either compiled or installed tools, though I'm still on spirv-tools v2025.2

[jre0]

Thanks for checking it out! It turns out, the error appears to only happen if the file contains other entry points. I had a task and fragment shader in the same file. When I removed them, it compiles fine! Would you expect that to be the case? With other kinds of shaders, I can put them in the same file.