Fix GLSL memory layout qualifiers not applied to uniform buffers or cbuffers (#7740)

* Fix GLSL memory layout qualifiers not applied to uniform buffers or cbuffers

The `layout(scalar)` qualifier was being ignored for GLSL `uniform` blocks and
HLSL `cbuffer` declarations, causing them to use std140 layout instead of the
requested scalar layout.

**Root Cause**:
The parsing logic in `slang-parser.cpp` handled layout qualifiers inconsistently:
- GLSL `buffer` blocks correctly used `getLayoutArg()` to map layout modifiers
- GLSL `uniform` blocks and HLSL `cbuffer` skipped layout arguments entirely

**Solution**:
- Enhanced `parseHLSLCBufferDecl()` to check for GLSL layout qualifiers
- Added same `getLayoutArg()` logic used by buffer blocks
- Modified uniform block parsing to pass layout arguments through

**Testing**:
- Added comprehensive test case: `tests/glsl/layout-scalar-qualifier.slang`
- Verified fix works for both `uniform` blocks and `cbuffer` declarations
- Confirmed no regressions in existing test suite

**Before**: `layout(scalar) uniform {...}` → std140 layout (32 bytes, offset 0,16)
**After**: `layout(scalar) uniform {...}` → scalar layout (16 bytes, offset 0,4)

Fixes #7735

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: pdeayton-nv <pdeayton-nv@users.noreply.github.com>

* Apply code formatting to slang-parser.cpp

Fixed line wrapping, trailing whitespace, and parameter formatting
according to repository style guidelines.

Co-authored-by: Harsh Aggarwal (NVIDIA) <szihs@users.noreply.github.com>

* format code (#7742)

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

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: pdeayton-nv <pdeayton-nv@users.noreply.github.com>
Co-authored-by: Harsh Aggarwal (NVIDIA) <szihs@users.noreply.github.com>
Co-authored-by: slangbot <ellieh+slangbot@nvidia.com>
Co-authored-by: slangbot <186143334+slangbot@users.noreply.github.com>
Co-authored-by: Yong He <yonghe@outlook.com>

2 files changed, 69 insertions, 1 deletions

diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index 0efa6a4b3..590954bd2 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -3578,9 +3578,36 @@ static Decl* ParseBufferBlockDecl(
 
 static NodeBase* parseHLSLCBufferDecl(Parser* parser, void* /*userData*/)
 {
+    // Check for GLSL layout qualifiers when GLSL input is allowed
+    if (parser->options.allowGLSLInput && parser->pendingModifiers)
+    {
+        auto getLayoutArg = [&](const char* defaultLayout)
+        {
+            if (auto dataLayoutMod =
+                    parser->pendingModifiers->findModifier<GLSLBufferDataLayoutModifier>())
+            {
+                if (as<GLSLStd140Modifier>(dataLayoutMod))
+                    return "Std140DataLayout";
+                else if (as<GLSLStd430Modifier>(dataLayoutMod))
+                    return "Std430DataLayout";
+                else if (as<GLSLScalarModifier>(dataLayoutMod))
+                    return "ScalarDataLayout";
+            }
+            return defaultLayout;
+        };
+
+        String layoutType = getLayoutArg("Std140DataLayout");
+        return ParseBufferBlockDecl(parser, "ConstantBuffer", &layoutType);
+    }
+
     return ParseBufferBlockDecl(parser, "ConstantBuffer");
 }
 
+static NodeBase* parseHLSLCBufferDeclWithLayout(Parser* parser, String layoutType)
+{
+    return ParseBufferBlockDecl(parser, "ConstantBuffer", &layoutType);
+}
+
 static NodeBase* parseHLSLTBufferDecl(Parser* parser, void* /*userData*/)
 {
     return ParseBufferBlockDecl(parser, "TextureBuffer");
@@ -4994,7 +5021,9 @@ static DeclBase* ParseDeclWithModifiers(
 
                     if (as<HLSLUniformModifier>(mod))
                     {
-                        decl = as<Decl>(parseHLSLCBufferDecl(parser, nullptr));
+                        decl = as<Decl>(parseHLSLCBufferDeclWithLayout(
+                            parser,
+                            getLayoutArg("Std140DataLayout")));
                         break;
                     }
                     else
diff --git a/tests/glsl/layout-scalar-qualifier.slang b/tests/glsl/layout-scalar-qualifier.slang
new file mode 100644
index 000000000..ac7b34d8b
--- /dev/null
+++ b/tests/glsl/layout-scalar-qualifier.slang
@@ -0,0 +1,39 @@
+//TEST:SIMPLE(filecheck=CHECK): -allow-glsl -target spirv-asm
+
+RWStructuredBuffer<uint> result;
+
+// Test GLSL uniform block with scalar layout qualifier
+// CHECK: SLANG_ParameterGroup_Data_uniform_natural
+// CHECK: OpMemberDecorate %SLANG_ParameterGroup_Data_uniform_natural 0 Offset 0
+// CHECK: OpMemberDecorate %SLANG_ParameterGroup_Data_uniform_natural 1 Offset 4
+layout(scalar) uniform Data_uniform {
+    uint a;
+    uint3 b;
+};
+
+// Test HLSL cbuffer with scalar layout qualifier  
+// CHECK: SLANG_ParameterGroup_Data_cbuffer_natural
+// CHECK: OpMemberDecorate %SLANG_ParameterGroup_Data_cbuffer_natural 0 Offset 0
+// CHECK: OpMemberDecorate %SLANG_ParameterGroup_Data_cbuffer_natural 1 Offset 4
+layout(scalar) cbuffer Data_cbuffer {
+    uint c;
+    uint3 d;
+};
+
+// Reference: ScalarDataLayout should work correctly
+struct Data {
+    uint e;
+    uint3 f;
+};
+ConstantBuffer<Data, ScalarDataLayout> Data_ConstantBufferScalarDataLayout;
+
+[shader("compute")]
+[numthreads(1,1,1)]
+void computeMain(uint3 threadId : SV_DispatchThreadID)
+{
+    uint index = threadId.x;
+    result[index] = 
+        a + b.x +
+        c + d.y +
+        Data_ConstantBufferScalarDataLayout.e + Data_ConstantBufferScalarDataLayout.f.z;
+}
\ No newline at end of file