test(cts): add coverage for clip-distances feature

Author: ErichDonGubler

cts_runner/test.lst

@@ -32,6 +32,7 @@ fails-if(vulkan) webgpu:api,operation,vertex_state,correctness:array_stride_zero
 webgpu:api,operation,vertex_state,correctness:setVertexBuffer_offset_and_attribute_offset:*
 webgpu:api,validation,buffer,create:*
 webgpu:api,validation,buffer,destroy:*
+webgpu:api,validation,capability_checks,features,clip_distances:*
 fails-if(dx12) webgpu:api,validation,capability_checks,limits,maxBindGroups:setBindGroup,*
 // NOTE: Only test some of these `maxInterStageShaderVariables` cases, because of a CTS bug (see
 // below). CTS (incorrectly) only deducts once for any set of them being enabled, but it should
@@ -207,6 +208,7 @@ webgpu:shader,execution,flow_control,return:*
 // Many other vertex_buffer_access subtests also passing, but there are too many to enumerate.
 // Fails on Metal in CI only, not when running locally.
 fails-if(metal) webgpu:shader,execution,robust_access_vertex:vertex_buffer_access:indexed=true;indirect=false;drawCallTestParameter="baseVertex";type="float32x4";additionalBuffers=4;partialLastNumber=false;offsetVertexBuffer=true
+webgpu:shader,execution,shader_io,vertex_builtins:outputs,clip_distances:*
 webgpu:shader,validation,const_assert,const_assert:*
 webgpu:shader,validation,expression,binary,short_circuiting_and_or:array_override:op="%26%26";a_val=1;b_val=1
 webgpu:shader,validation,expression,binary,short_circuiting_and_or:invalid_types:*

wgpu-core/src/validation.rs

@@ -1141,7 +1141,12 @@ impl Interface {
                 debug_assert_eq!(stride, 4);
 
                 let naga::ArraySize::Constant(array_size) = size else {
-                    // TODO: Should we accept override expressions?
+                    // NOTE: Based on the
+                    // [spec](https://gpuweb.github.io/gpuweb/wgsl/#fixed-footprint-types):
+                    //
+                    // > The only valid use of a fixed-size array with an element count that is an
+                    // > override-expression that is not a const-expression is as a memory view in
+                    // > the workgroup address space.
                     unreachable!("non-constant array size for `clip_distances`")
                 };
                 let array_size = array_size.get();