MSL: Emit interface block members of array length 1 as arrays instead of scalars.

Test for array presence using is_array() instead of element count.
Add shaders-msl/vert/interface-block-single-element-array.vert regression test.

Fixes a regression error introduced in 3d4daab.

reference/opt/shaders-msl/vert/interface-block-single-element-array.vert

@@ -0,0 +1,79 @@
+#pragma clang diagnostic ignored "-Wmissing-prototypes"
+#pragma clang diagnostic ignored "-Wmissing-braces"
+
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+template<typename T, size_t Num>
+struct spvUnsafeArray
+{
+    T elements[Num ? Num : 1];
+    
+    thread T& operator [] (size_t pos) thread
+    {
+        return elements[pos];
+    }
+    constexpr const thread T& operator [] (size_t pos) const thread
+    {
+        return elements[pos];
+    }
+    
+    device T& operator [] (size_t pos) device
+    {
+        return elements[pos];
+    }
+    constexpr const device T& operator [] (size_t pos) const device
+    {
+        return elements[pos];
+    }
+    
+    constexpr const constant T& operator [] (size_t pos) const constant
+    {
+        return elements[pos];
+    }
+    
+    threadgroup T& operator [] (size_t pos) threadgroup
+    {
+        return elements[pos];
+    }
+    constexpr const threadgroup T& operator [] (size_t pos) const threadgroup
+    {
+        return elements[pos];
+    }
+};
+
+struct TDPickVertex
+{
+    float4 c;
+    spvUnsafeArray<float3, 1> uv;
+};
+
+struct main0_out
+{
+    float4 oTDVert_c [[user(locn0)]];
+    float3 oTDVert_uv_0 [[user(locn1)]];
+    float4 gl_Position [[position]];
+};
+
+struct main0_in
+{
+    float3 P [[attribute(0)]];
+    float3 uv_0 [[attribute(1)]];
+};
+
+vertex main0_out main0(main0_in in [[stage_in]])
+{
+    main0_out out = {};
+    TDPickVertex oTDVert = {};
+    spvUnsafeArray<float3, 1> uv = {};
+    uv[0] = in.uv_0;
+    out.gl_Position = float4(in.P, 1.0);
+    oTDVert.uv[0] = uv[0];
+    oTDVert.c = float4(1.0);
+    out.oTDVert_c = oTDVert.c;
+    out.oTDVert_uv_0 = oTDVert.uv[0];
+    return out;
+}
+

reference/shaders-msl/vert/interface-block-single-element-array.vert

@@ -0,0 +1,79 @@
+#pragma clang diagnostic ignored "-Wmissing-prototypes"
+#pragma clang diagnostic ignored "-Wmissing-braces"
+
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+template<typename T, size_t Num>
+struct spvUnsafeArray
+{
+    T elements[Num ? Num : 1];
+    
+    thread T& operator [] (size_t pos) thread
+    {
+        return elements[pos];
+    }
+    constexpr const thread T& operator [] (size_t pos) const thread
+    {
+        return elements[pos];
+    }
+    
+    device T& operator [] (size_t pos) device
+    {
+        return elements[pos];
+    }
+    constexpr const device T& operator [] (size_t pos) const device
+    {
+        return elements[pos];
+    }
+    
+    constexpr const constant T& operator [] (size_t pos) const constant
+    {
+        return elements[pos];
+    }
+    
+    threadgroup T& operator [] (size_t pos) threadgroup
+    {
+        return elements[pos];
+    }
+    constexpr const threadgroup T& operator [] (size_t pos) const threadgroup
+    {
+        return elements[pos];
+    }
+};
+
+struct TDPickVertex
+{
+    float4 c;
+    spvUnsafeArray<float3, 1> uv;
+};
+
+struct main0_out
+{
+    float4 oTDVert_c [[user(locn0)]];
+    float3 oTDVert_uv_0 [[user(locn1)]];
+    float4 gl_Position [[position]];
+};
+
+struct main0_in
+{
+    float3 P [[attribute(0)]];
+    float3 uv_0 [[attribute(1)]];
+};
+
+vertex main0_out main0(main0_in in [[stage_in]])
+{
+    main0_out out = {};
+    TDPickVertex oTDVert = {};
+    spvUnsafeArray<float3, 1> uv = {};
+    uv[0] = in.uv_0;
+    out.gl_Position = float4(in.P, 1.0);
+    oTDVert.uv[0] = uv[0];
+    oTDVert.c = float4(1.0);
+    out.oTDVert_c = oTDVert.c;
+    out.oTDVert_uv_0 = oTDVert.uv[0];
+    return out;
+}
+

shaders-msl/vert/interface-block-single-element-array.vert

@@ -0,0 +1,17 @@
+#version 460
+
+layout(location = 0) out TDPickVertex
+{
+vec4 c;
+vec3 uv[1];
+} oTDVert;
+
+layout(location = 0) in vec3 P;
+layout(location = 1) in vec3 uv[1];
+
+void main()
+{
+gl_Position = vec4(P, 1.0);
+oTDVert.uv[0] = uv[0];
+oTDVert.c = vec4(1.);
+}

spirv_msl.cpp

@@ -2580,12 +2580,14 @@ void CompilerMSL::add_composite_member_variable_to_interface_block(StorageClass
 	uint32_t mbr_type_id = var_type.member_types[mbr_idx];
 	auto &mbr_type = get<SPIRType>(mbr_type_id);
 
+	bool mbr_is_indexable = false;
 	uint32_t elem_cnt = 1;
 	if (is_matrix(mbr_type))
 	{
 		if (is_array(mbr_type))
 			SPIRV_CROSS_THROW("MSL cannot emit arrays-of-matrices in input and output variables.");
 
+		mbr_is_indexable = true;
 		elem_cnt = mbr_type.columns;
 	}
 	else if (is_array(mbr_type))
@@ -2593,6 +2595,7 @@ void CompilerMSL::add_composite_member_variable_to_interface_block(StorageClass
 		if (mbr_type.array.size() != 1)
 			SPIRV_CROSS_THROW("MSL cannot emit arrays-of-arrays in input and output variables.");
 
+		mbr_is_indexable = true;
 		elem_cnt = to_array_size_literal(mbr_type);
 	}
 
@@ -2628,8 +2631,8 @@ void CompilerMSL::add_composite_member_variable_to_interface_block(StorageClass
 	{
 		for (uint32_t i = 0; i < elem_cnt; i++)
 		{
-			string mbr_name = append_member_name(mbr_name_qual, var_type, mbr_idx) + (elem_cnt == 1 ? "" : join("_", i));
-			string var_chain = join(var_chain_qual, ".", to_member_name(var_type, mbr_idx), (elem_cnt == 1 ? "" : join("[", i, "]")));
+			string mbr_name = append_member_name(mbr_name_qual, var_type, mbr_idx) + (mbr_is_indexable ? join("_", i) : "");
+			string var_chain = join(var_chain_qual, ".", to_member_name(var_type, mbr_idx), (mbr_is_indexable ? join("[", i, "]") : ""));
 			uint32_t sub_mbr_cnt = uint32_t(mbr_type.member_types.size());
 			for (uint32_t sub_mbr_idx = 0; sub_mbr_idx < sub_mbr_cnt; sub_mbr_idx++)
 			{
@@ -2654,7 +2657,7 @@ void CompilerMSL::add_composite_member_variable_to_interface_block(StorageClass
 			ib_type.member_types.push_back(usable_type->self);
 
 		// Give the member a name
-		string mbr_name = ensure_valid_name(append_member_name(mbr_name_qual, var_type, mbr_idx) + (elem_cnt == 1 ? "" : join("_", i)), "m");
+		string mbr_name = ensure_valid_name(append_member_name(mbr_name_qual, var_type, mbr_idx) + (mbr_is_indexable ? join("_", i) : ""), "m");
 		set_member_name(ib_type.self, ib_mbr_idx, mbr_name);
 
 		// Once we determine the location of the first member within nested structures,
@@ -2718,7 +2721,7 @@ void CompilerMSL::add_composite_member_variable_to_interface_block(StorageClass
 		// Unflatten or flatten from [[stage_in]] or [[stage_out]] as appropriate.
 		if (!meta.strip_array && meta.allow_local_declaration)
 		{
-			string var_chain = join(var_chain_qual, ".", to_member_name(var_type, mbr_idx), (elem_cnt == 1 ? "" : join("[", i, "]")));
+			string var_chain = join(var_chain_qual, ".", to_member_name(var_type, mbr_idx), (mbr_is_indexable ? join("[", i, "]") : ""));
 			switch (storage)
 			{
 			case StorageClassInput: