Support interpolation modifiers for WGSL (#5641)

* wgsl: Support interpolation modifiers

* Move struct key decorations to flattened structs.
** This includes interpolation mode decorations, which must be in the flattened struct.
* Emit interpolation attribute.
* Enable tests/render/nointerpolation.hlsl for WGSL, as a result.

This closes #5625.

* Add new expected output for 'nointerpolation' test

7 files changed, 63 insertions, 5 deletions

diff --git a/source/slang/slang-emit-wgsl.cpp b/source/slang/slang-emit-wgsl.cpp
index fcc4b615f..d49986263 100644
--- a/source/slang/slang-emit-wgsl.cpp
+++ b/source/slang/slang-emit-wgsl.cpp
@@ -1506,4 +1506,53 @@ void WGSLSourceEmitter::emitIntrinsicCallExprImpl(
         inOuterPrec);
 }
 
+void WGSLSourceEmitter::emitInterpolationModifiersImpl(
+    IRInst* varInst,
+    IRType* /* valueType */,
+    IRVarLayout* /* layout */)
+{
+    char const* interpolationType = nullptr;
+    char const* interpolationSampling = nullptr;
+    for (auto dd : varInst->getDecorations())
+    {
+        if (dd->getOp() != kIROp_InterpolationModeDecoration)
+            continue;
+        auto decoration = (IRInterpolationModeDecoration*)dd;
+        IRInterpolationMode mode = decoration->getMode();
+        switch (mode)
+        {
+        case IRInterpolationMode::NoInterpolation:
+            interpolationType = "flat";
+            break;
+        case IRInterpolationMode::NoPerspective:
+        case IRInterpolationMode::Linear:
+            interpolationType = "linear";
+            break;
+        case IRInterpolationMode::Sample:
+            interpolationSampling = "sample";
+            break;
+        case IRInterpolationMode::Centroid:
+            interpolationSampling = "centroid";
+            break;
+        }
+    }
+
+    if (interpolationType)
+    {
+        m_writer->emit("@interpolate(");
+        m_writer->emit(interpolationType);
+        if (interpolationSampling)
+        {
+            m_writer->emit(", ");
+            m_writer->emit(interpolationSampling);
+        }
+        m_writer->emit(") ");
+    }
+
+    // TODO: Check the following:
+    // "User-defined vertex outputs and fragment inputs of scalar or vector
+    //  integer type must always be specified with interpolation type flat."
+    // https://www.w3.org/TR/WGSL/#interpolation
+}
+
 } // namespace Slang
diff --git a/source/slang/slang-emit-wgsl.h b/source/slang/slang-emit-wgsl.h
index 6ff9e6786..0cbedf4eb 100644
--- a/source/slang/slang-emit-wgsl.h
+++ b/source/slang/slang-emit-wgsl.h
@@ -42,6 +42,10 @@ public:
     virtual void emitStructFieldAttributes(IRStructType* structType, IRStructField* field)
         SLANG_OVERRIDE;
     virtual void emitCallArg(IRInst* inst) SLANG_OVERRIDE;
+    virtual void emitInterpolationModifiersImpl(
+        IRInst* varInst,
+        IRType* valueType,
+        IRVarLayout* layout) SLANG_OVERRIDE;
 
     virtual void emitIntrinsicCallExprImpl(
         IRCall* inst,
diff --git a/source/slang/slang-ir-wgsl-legalize.cpp b/source/slang/slang-ir-wgsl-legalize.cpp
index 4d5f6e4ba..facafb284 100644
--- a/source/slang/slang-ir-wgsl-legalize.cpp
+++ b/source/slang/slang-ir-wgsl-legalize.cpp
@@ -629,7 +629,10 @@ struct LegalizeWGSLEntryPointContext
         // 2. If IRStructType:
         //  2a. Recurse this function with 'decorations that carry semantic info' from parent.
         // 3. If not IRStructType:
-        //  3a. Emit 'newField' equal to 'oldField', add 'decorations which carry semantic info'.
+        //  3a. Emit 'newField' with 'newKey' equal to 'oldField' and 'oldKey', respectively,
+        //      where 'oldKey' is the key corresponding to 'oldField'.
+        //      Add 'decorations which carry semantic info' to 'newField', and move all decorations
+        //      of 'oldKey' to 'newKey'.
         //  3b. Store a mapping from 'oldField' to 'newField' in 'mapFieldToField'. This info is
         //  needed to copy between types.
         for (auto oldField : src->getFields())
@@ -674,7 +677,7 @@ struct LegalizeWGSLEntryPointContext
 
             // step 3a
             auto newKey = builder.createStructKey();
-            copyNameHintAndDebugDecorations(newKey, oldKey);
+            oldKey->transferDecorationsTo(newKey);
 
             auto newField = builder.createStructField(dst, newKey, oldField->getFieldType());
             copyNameHintAndDebugDecorations(newField, oldField);
diff --git a/tests/expected-failure-github.txt b/tests/expected-failure-github.txt
index 671b8dafd..ee96de7f5 100644
--- a/tests/expected-failure-github.txt
+++ b/tests/expected-failure-github.txt
@@ -20,4 +20,3 @@ tests/language-feature/generics/variadic-0.slang.4 syn (wgpu)
 tests/language-feature/shader-params/interface-shader-param-ordinary.slang.4 syn (wgpu)
 tests/language-feature/swizzles/matrix-swizzle-write-array.slang.3 syn (wgpu)
 tests/language-feature/swizzles/matrix-swizzle-write-swizzle.slang.3 syn (wgpu)
-tests/render/nointerpolation.hlsl (wgpu)
diff --git a/tests/render/nointerpolation.hlsl b/tests/render/nointerpolation.hlsl
index a8d0c85e0..d514379d0 100644
--- a/tests/render/nointerpolation.hlsl
+++ b/tests/render/nointerpolation.hlsl
@@ -1,6 +1,4 @@
 //TEST(smoke):COMPARE_HLSL_RENDER:
-// WGSL: nointerpolate doesn't work #5625
-//DISABLE_TEST(smoke):COMPARE_HLSL_RENDER: -wgpu
 // TODO: Investigate Metal failure
 //DISABLE_TEST(smoke):COMPARE_HLSL_RENDER: -mtl
 
diff --git a/tests/render/nointerpolation.hlsl.3.expected b/tests/render/nointerpolation.hlsl.3.expected
new file mode 100644
index 000000000..4c32e2510
--- /dev/null
+++ b/tests/render/nointerpolation.hlsl.3.expected
@@ -0,0 +1,5 @@
+result code = 0
+standard error = {
+}
+standard output = {
+}
diff --git a/tests/render/nointerpolation.hlsl.3.expected.png b/tests/render/nointerpolation.hlsl.3.expected.png
new file mode 100644
index 000000000..793b27c19
--- /dev/null
+++ b/tests/render/nointerpolation.hlsl.3.expected.png