Fix issue where inter-stage parameters without semantics don't get location attributes (#5670)

* wgsl: Make sure each shader input field has a semantic

This closes #5633.

* Add test for inter-stage variables without semantics

This verifies the fix of the second issue identified in
https://github.com/shader-slang/slang/issues/5633

* format code

---------

Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>

3 files changed, 82 insertions, 0 deletions

diff --git a/tests/render/multiple-stage-io-locations-without-user-semantics.slang b/tests/render/multiple-stage-io-locations-without-user-semantics.slang
new file mode 100644
index 000000000..af0e3e39f
--- /dev/null
+++ b/tests/render/multiple-stage-io-locations-without-user-semantics.slang
@@ -0,0 +1,77 @@
+// TODO: Investigate failures on non-WebGPU backends
+//TEST(smoke,render):COMPARE_HLSL_RENDER: -wgpu
+
+cbuffer Uniforms
+{
+    float4x4 modelViewProjection;
+}
+
+struct AssembledVertex
+{
+    float3 position;
+    float3 color;
+};
+
+struct Fragment
+{
+    float4 color;
+};
+
+// Vertex  Shader
+
+struct VertexStageInput
+{
+    AssembledVertex assembledVertex : A;
+};
+
+struct VertexStageOutput
+{
+    float3 color;
+    float3 localPosition;
+    float4 sv_position     : SV_Position;
+};
+
+VertexStageOutput vertexMain(VertexStageInput input)
+{
+    VertexStageOutput output;
+
+    float3 position = input.assembledVertex.position;
+    float3 color    = input.assembledVertex.color;
+
+    output.color         = color;
+    output.sv_position   = mul(modelViewProjection, float4(position, 1.0));
+    output.localPosition = position;
+
+    return output;
+}
+
+// Fragment Shader
+
+struct FragmentStageInput
+{
+    float3 color;
+    float3 localPosition;
+};
+
+struct FragmentStageOutput
+{
+    Fragment fragment : SV_Target;
+};
+
+FragmentStageOutput fragmentMain(FragmentStageInput input)
+{
+    FragmentStageOutput output;
+
+    float3 color = input.color;
+
+    if (input.color.y < input.color.z)
+    {
+        output.fragment.color = float4(input.localPosition, 1.0);
+    }
+    else
+    {
+        output.fragment.color = float4(input.color, 1.0);
+    }
+
+    return output;
+}
diff --git a/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected b/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected
new file mode 100644
index 000000000..4c32e2510
--- /dev/null
+++ b/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected
@@ -0,0 +1,5 @@
+result code = 0
+standard error = {
+}
+standard output = {
+}
diff --git a/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected.png b/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected.png
new file mode 100644
index 000000000..3333a12d7
--- /dev/null
+++ b/tests/render/multiple-stage-io-locations-without-user-semantics.slang.expected.png