SceneKit Metal shader no longer compiles in Xcode 13.

I have an app developed as a SceneKit AR app. It has been fine for a long time but in XCode 13 the shader now fails to compile and results in the dreaded purple shader of death in-app.

It was modified from the simple mesh shader included in Apple's original ARKit example app.

#include <metal_stdlib>
#include <simd/simd.h>

#pragma body
#pragma transparent

uniform simd_float2 worldDimensions;

const float numTiles = 40.0;
const float tilePercent = 1.0 / numTiles;
const float edgeThickness = (1.0 / numTiles) * 0.05;

The first error I get now is the following:

[SceneKit] Error: FATAL ERROR : failed compiling shader:
Error Domain=MTLLibraryErrorDomain Code=3 "program_source:3179:50: error: unknown type name 'simd_float2'
                                      , constant simd_float2& worldDimensions

If I change this from simd_float2 to float2 then the error explodes into the larger cascade of:

[SceneKit] Error: FATAL ERROR : failed compiling shader:
Error Domain=MTLLibraryErrorDomain Code=3 "program_source:992:1: error: use of class template 'uniform' requires template arguments
uniform float2 worldDimensions;
^
/System/Library/PrivateFrameworks/GPUCompiler.framework/Libraries/lib/clang/31001.325/include/metal/metal_uniform:16:8: note: template is declared here
struct uniform;
       ^
program_source:992:15: error: expected ';' after top level declarator
uniform float2 worldDimensions;

At this point I'm unable to see anything in the XCode changelogs etc. that offer any assistance as to what has changed in the spec. Any help gratefully appreciated.

The entire shader:

#include <metal_stdlib>
#include <simd/simd.h>

#pragma body
#pragma transparent

uniform float2 worldDimensions;

const float numTiles = 40.0;
const float tilePercent = 1.0 / numTiles;
const float edgeThickness = (1.0 / numTiles) * 0.05;

const simd_float2 cm10 = worldDimensions * 10.0;

float u = _surface.diffuseTexcoord.x * (1.0 + edgeThickness);
float v = _surface.diffuseTexcoord.y * (1.0 + edgeThickness);

const float2 thicknessMajor = float2(0.005, 0.005) / worldDimensions;
const float2 thicknessMinor = float2(0.005, 0.005) / worldDimensions;

bool onMeter = (fmod(u, 1.0 / worldDimensions.x) < thicknessMajor.x) || (fmod(v, 1.0 / worldDimensions.y) < thicknessMajor.y);

onMeter = onMeter || (u > 1.0 - thicknessMajor.x) || (v > 1.0 - thicknessMajor.y);

bool onCM = (fmod(u, 1.0 / cm10.x) < thicknessMinor.x) || (fmod(v, 1.0 / cm10.y) < thicknessMinor.y);

float4 defaultColor = _surface.diffuse;

float alpha = onMeter ? 0.7 : 0.1;

float4 outColor = float4(defaultColor.xyz, 1.0);
_surface.diffuse = float4(outColor.xyz, alpha);
_surface.transparent = float4(1.0, 1.0, 1.0, alpha);

if (!onCM && !onMeter)
    discard_fragment();