Fix combined sampler documentation and warning (#6207)

* Fix combined sampler documentation and warning

* Update comment, show detailed '-fvk-t-shift' message in warning instead of generic '-fvk-xxx-shift'

* format code

---------

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

2 files changed, 38 insertions, 3 deletions

diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index cf338edfa..345be7a54 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -2019,6 +2019,13 @@ DIAGNOSTIC(
     notValidVaryingParameter,
     "parameter '$0' is not a valid varying parameter.")
 
+DIAGNOSTIC(
+    39029,
+    Warning,
+    registerModifierButNoVkBindingNorShift,
+    "shader parameter '$0' has a 'register' specified for D3D, but no '[[vk::binding(...)]]` "
+    "specified for Vulkan, nor is `-fvk-$1-shift` used.")
+
 //
 
 // 4xxxx - IL code generation.
diff --git a/source/slang/slang-parameter-binding.cpp b/source/slang/slang-parameter-binding.cpp
index 55c487e4e..61226f898 100644
--- a/source/slang/slang-parameter-binding.cpp
+++ b/source/slang/slang-parameter-binding.cpp
@@ -1078,10 +1078,32 @@ static void _maybeDiagnoseMissingVulkanLayoutModifier(
     // oversight on their part.
     if (auto registerModifier = varDecl.getDecl()->findModifier<HLSLRegisterSemantic>())
     {
+        auto varType = getType(context->getASTBuilder(), varDecl.as<VarDeclBase>());
+        if (auto textureType = as<TextureType>(varType))
+        {
+            if (textureType->isCombined())
+            {
+                // Recommend [[vk::binding]] but not '-fvk-xxx-shift` for combined texture samplers
+                getSink(context)->diagnose(
+                    registerModifier,
+                    Diagnostics::registerModifierButNoVulkanLayout,
+                    varDecl.getName());
+                return;
+            }
+        }
+
+        UnownedStringSlice registerClassName;
+        UnownedStringSlice registerIndexDigits;
+        splitNameAndIndex(
+            registerModifier->registerName.getContent(),
+            registerClassName,
+            registerIndexDigits);
+
         getSink(context)->diagnose(
             registerModifier,
-            Diagnostics::registerModifierButNoVulkanLayout,
-            varDecl.getName());
+            Diagnostics::registerModifierButNoVkBindingNorShift,
+            varDecl.getName(),
+            registerClassName);
     }
 }
 
@@ -1256,7 +1278,6 @@ static void addExplicitParameterBindings_GLSL(
         return;
     }
 
-
     const auto hlslInfo = _extractLayoutSemanticInfo(context, hlslRegSemantic);
     if (hlslInfo.kind == LayoutResourceKind::None)
     {
@@ -1270,7 +1291,14 @@ static void addExplicitParameterBindings_GLSL(
     if (auto textureType = as<TextureType>(varType))
     {
         if (textureType->isCombined())
+        {
+            if (!warnedMissingVulkanLayoutModifier)
+            {
+                _maybeDiagnoseMissingVulkanLayoutModifier(context, varDecl.as<VarDeclBase>());
+                warnedMissingVulkanLayoutModifier = true;
+            }
             return;
+        }
     }
 
     // Can we map to a Vulkan kind in principal?