MoltenVK/SPIRV-Cross fails repacking nested cbuffer structs

[farzonl]

Reproduction

https://godbolt.org/z/96E5qqG3r

Description of issue

A compute shader that reads from an HLSL cbuffer containing nested structs (including a derived struct Y : X and arrays like Z { X xs[2]; Y y; } and Z zs[2]) triggers MoltenVK’s SPIR-V→MSL path to attempt struct repacking, but it aborts when the repacked struct is itself a member of another struct. This results in SPIR-V to MSL conversion error: Cannot perform any repacking for structs when it is used as a member of another struct and pipeline creation fails with VK_ERROR_INITIALIZATION_FAILED.

HLSL Source

dxc-3.7 -spirv -fspv-target-env=vulkan1.3 -fvk-use-dx-layout -T cs_6_5 source.hlsl > structs.test.spv

struct X {
  int a1;
};

struct Y : X {
  int2 a2;
};

struct Z {
  X xs[2];
  Y y;
};

cbuffer CBStructs : register(b0) {
  X x1;
  X x2;
  Y y;
  Z zs[2];
};

struct S {
  int x1a1;
  int x2a1;
  int ya1;
  int2 ya2;
  int z1x1a1;
  int z1x2a1;
  int z1ya1;
  int2 z1ya2;
  int z2x1a1;
  int z2x2a1;
  int z2ya1;
  int2 z2ya2;
};

RWStructuredBuffer<S> Out : register(u1);

[numthreads(1,1,1)]
void main() {
 Out[0].x1a1 = x1.a1;
 Out[0].x2a1 = x2.a1;
 Out[0].ya1 = y.a1;
 Out[0].ya2 = y.a2;
 Out[0].z1x1a1 = zs[0].xs[0].a1;
 Out[0].z1x2a1 = zs[0].xs[1].a1;
 Out[0].z1ya1 = zs[0].y.a1;
 Out[0].z1ya2 = zs[0].y.a2;
 Out[0].z2x1a1 = zs[1].xs[0].a1;
 Out[0].z2x2a1 = zs[1].xs[1].a1;
 Out[0].z2ya1 = zs[1].y.a1;
 Out[0].z2ya2 = zs[1].y.a2;
}

Errors

[mvk-error] SPIR-V to MSL conversion error: Cannot perform any repacking for structs when it is used as a member of another struct.
[mvk-error] VK_ERROR_INITIALIZATION_FAILED: Compute shader function could not be compiled into pipeline. See previous logged error.