Add a diagnostic check to warn when special types leak from param groups

As part of type legalization, certain special types may be removed from
parameter group types. For example, in the following structure:

    [vk::push_constants]
    cbuffer PushConstants {
        int i;
        RaytracingAccelerationStructure rtas;
    }

`rtas` cannot be included in this structure, and will leak out to a
different binding. Warn the user when this happens.

Fixes #8818

Author: zangold-nv

source/slang/slang-diagnostic-defs.h

@@ -1178,6 +1178,17 @@ DIAGNOSTIC(
     imageFormatUnsupportedByBackend,
     "Image format '$0' is not explicitly supported by the $1 backend, using supported format '$2' "
     "instead.")
+DIAGNOSTIC(
+    31106,
+    Warning,
+    specialTypeLeaksFromParameterGroup,
+    "Parameter group type includes some members with types which cannot be included in the same "
+    "binding. These types will be moved into another parameter binding slot.")
+DIAGNOSTIC(
+    31107,
+    Warning,
+    specialTypeLeaksFromParameterGroupElement,
+    "Structure member will leak into separate binding.")
 
 DIAGNOSTIC(31120, Error, invalidAttributeTarget, "invalid syntax target for user defined attribute")
 DIAGNOSTIC(

source/slang/slang-legalize-types.cpp

@@ -1225,6 +1225,25 @@ LegalType legalizeTypeImpl(TypeLegalizationContext* context, IRType* type)
         else
         {
             legalElementType = legalizeType(context, originalElementType);
+
+            // When special types leak out of a parameter group, they need to
+            // be bound differently. Warn the user when this happens.
+            if (legalElementType.flavor == LegalType::Flavor::pair)
+            {
+                context->m_sink->diagnose(
+                    findFirstUseLoc(type),
+                    Diagnostics::specialTypeLeaksFromParameterGroup);
+
+                // indicate which elements cannot be part of the parameter group
+                for (auto specialElement :
+                     legalElementType.getPair()->specialType.getTuple()->elements)
+                {
+                    context->m_sink->diagnose(
+                        specialElement.key,
+                        Diagnostics::specialTypeLeaksFromParameterGroupElement);
+                }
+            }
+
             // As a bit of a corner case, if the user requested something
             // like `ConstantBuffer<Texture2D>` the element type would
             // legalize to a "simple" type, and that would be interpreted

tests/diagnostics/rtas-cbuff-leak.slang

@@ -0,0 +1,13 @@
+//DIAGNOSTIC_TEST:SIMPLE: -entry computeMain -stage compute -target spirv -preserve-params
+
+// RTAS can't be a part of this binding, and will leak to a different binding.
+[vk::push_constant]
+cbuffer PushConstants {
+    int i;
+    RaytracingAccelerationStructure rtas;
+};
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+}

tests/diagnostics/rtas-cbuff-leak.slang.expected

@@ -0,0 +1,36 @@
+result code = 0
+standard error = {
+shader.slang(5): warning 31106: Parameter group type includes some members with types which cannot be included in the same binding. These types will be moved into another parameter binding slot.
+cbuffer PushConstants {
+        ^~~~~~~~~~~~~
+shader.slang(7): warning 31107: Structure member will leak into separate binding.
+    RaytracingAccelerationStructure rtas;
+                                    ^~~~
+}
+standard output = {
+; SPIR-V
+; Version: 1.5
+; Generator: Khronos Slang Compiler; 0
+; Bound: 12
+; Schema: 0
+OpCapability RayTracingKHR
+OpCapability Shader
+OpExtension "SPV_KHR_ray_tracing"
+OpMemoryModel Logical GLSL450
+OpEntryPoint GLCompute %computeMain "main"
+OpExecutionMode %computeMain LocalSize 1 1 1
+
+; Debug Information
+OpSource Slang 1
+OpName %computeMain "computeMain"                   ; id %9
+
+; Types, variables and constants
+%void = OpTypeVoid
+%10 = OpTypeFunction %void
+
+; Function computeMain
+%computeMain = OpFunction %void None %10
+%11 = OpLabel
+OpReturn
+OpFunctionEnd
+}