Add sample-rate-input detection for HLSL. (#312)

* Add sample-rate-input detection for HLSL.

In the HLSL case, it is possible to do this detection entirely based on declared signatures (it doesn't have a dependency on code generation like the GLSL case does). I've added test cases for the two main ways that a shader can become sample rate:

1. Qualify a fragment input with `sample`
2. Accept an input with the `SV_SampleIndex` semantic

In each case I nested the input inside a `struct` to try to match common HLSL idiom, and to make sure that we handle the nested case.

This code is *not* robust against shaders that declare such an input and then never use it, but that is to be expected given the goals for Slang.

* Fixup: add missing test output files

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/reflection/sample-index-input.hlsl b/tests/reflection/sample-index-input.hlsl
new file mode 100644
index 000000000..edb0690d6
--- /dev/null
+++ b/tests/reflection/sample-index-input.hlsl
@@ -0,0 +1,15 @@
+//TEST:REFLECTION:-profile ps_5_0 -target hlsl
+
+// Confirm that we register a shader as sample-rate when
+// it declares `SV_SampleIndex` as an input.
+
+struct PSInput
+{
+	float4 color : COLOR;
+	uint sampleIndex : SV_SampleIndex;	
+};
+
+float4 main(PSInput input) : SV_Target
+{
+	return input.color;
+}
\ No newline at end of file