mesh-node-missing-output-topology

Pre-v0 status: this rule page is published ahead of the implementation (preview / experimental, gated behind [experimental] work-graph-mesh-nodes = true in .shader-clippy.toml).

(via ADR 0010)

What it detects

A mesh node (function annotated [NodeLaunch("mesh")]) that lacks the [outputtopology(...)] attribute or that has it set to a value other than "triangle" / "line" (the values supported by the preview specification). Slang reflection identifies the node-launch kind; the rule walks the function attributes and fires on absence or invalid value.

Why it matters on a GPU

[outputtopology] tells the rasterizer how to interpret the index buffer the mesh shader emits — "triangle" means three indices per primitive, "line" means two. The preview Mesh Nodes spec inherits this attribute requirement directly from the standalone mesh-shader spec; the rasterizer wiring is the same on every IHV (Ada / RDNA 3 / Xe-HPG). Without the attribute, the runtime cannot wire the mesh node to the rasterizer because it doesn't know which primitive-assembly path to use.

The PSO link fails on every preview driver. The DXC validator catches the absence; the lint catches both the absence and the typo / unsupported value cases. The diagnostic names the missing or invalid attribute and lists the supported values.

Examples

Bad

hlsl

// Mesh node missing [outputtopology].
struct Record { uint payload; };

[Shader("node")]
[NodeLaunch("mesh")]
[NodeDispatchGrid(64, 1, 1)]
[numthreads(64, 1, 1)]
// missing [outputtopology(...)]
void MeshNode(
    [MaxRecords(64)] DispatchNodeInputRecord<Record> in,
    out vertices Vertex   verts[64],
    out indices  uint3    tris[124])
{
    /* ... */
}

Good

hlsl

[Shader("node")]
[NodeLaunch("mesh")]
[NodeDispatchGrid(64, 1, 1)]
[numthreads(64, 1, 1)]
[outputtopology("triangle")]
void MeshNode(
    [MaxRecords(64)] DispatchNodeInputRecord<Record> in,
    out vertices Vertex   verts[64],
    out indices  uint3    tris[124])
{
    /* ... */
}

Options

This rule is gated behind [experimental] work-graph-mesh-nodes = true in .shader-clippy.toml.

Fix availability

none — The right topology depends on the meshlet's index-buffer layout; the diagnostic names the missing attribute.

mesh-node-missing-output-topology ​

What it detects ​

Why it matters on a GPU ​

Examples ​

Bad ​

Good ​

Options ​

Fix availability ​

See also ​