RenderPassDescriptor fails for VS input/output only

I have a shader that sets rasterizationEnabled to NO on the MTLRenderPipeline. It's essentially using a vertex shader to do compute. This vertex shader reads vertex buffer data, and writes out to another buffer from within the same shader.

The problem is I don't know how to correctly wrap this in a render pass. The MTLRenderPass creation from a MTLRenderPassDescriptor complains that no width/height/format or renderTarget/depth is set on this pass. But it's not dependent on rasterization or render textures. What is the correct way to specify the enclosing RenderPass to Metal?

RenderPassDescriptor fails for VS input/output only
 
 
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