Add warning for ignored binding attributes on uniforms

When binding attributes (like [[vk::binding]]) are specified
on
uniforms that get packed into the default constant buffer, these binding
attributes are effectively ignored since the uniform will always be
placed
at descriptor set 0, binding 0. This can be confusing for users who
expect
their explicit bindings to take effect.

This change adds a new warning (71) that informs users when their
binding
attributes on uniforms will be ignored, and suggests declaring the
uniform
inside a constant buffer to preserve the explicit binding.

The warning helps users understand:
1. Why their binding attribute isn't having the expected effect
2. That the uniform is being packed into the default constant buffer
3. How to fix it by using a constant buffer declaration

Added test case in tests/bugs/binding-attribute-ignored.slang to verify
the warning behavior.

(cherry picked from commit 82f66e7)

Author: mkeshavaNV

source/slang/slang-diagnostic-defs.h

@@ -248,6 +248,12 @@ DIAGNOSTIC(
     "the output path '$0' is not associated with any entry point; a '-o' option for a compiled "
     "kernel must follow the '-entry' option for its corresponding entry point")
 
+DIAGNOSTIC(
+    71,
+    Warning,
+    bindingAttributeIgnoredOnUniform,
+    "binding attribute on uniform '$0' will be ignored since it will be packed into the default constant buffer at descriptor set 0 binding 0. To use explicit bindings, declare the uniform inside a constant buffer.")
+
 DIAGNOSTIC(
     80,
     Error,

source/slang/slang-parameter-binding.cpp

@@ -3511,34 +3511,17 @@ static void collectParameters(ParameterBindingContext* inContext, ComponentType*
 /// Emit a diagnostic about a uniform/ordinary parameter at global scope.
 void diagnoseGlobalUniform(SharedParameterBindingContext* sharedContext, VarDeclBase* varDecl)
 {
-    // This subroutine gets invoked if a shader parameter containing
-    // "ordinary" data (sometimes just called "uniform" data) is present
-    // at the global scope.
-    //
-    // Slang can support such parameters by aggregating them into
-    // an implicit constant buffer, but it is also common for programmers
-    // to accidentally declare a global-scope shader parameter when they
-    // meant to declare a global variable instead:
-    //
-    //      int gCounter = 0; // this is a shader parameter, not a global
-    //
-    // In order to avoid mistakes, we'd like to warn the user when
-    // they write code like the above, and hint to them that they
-    // should make their intention more explicit with a keyword:
-    //
-    //      static int gCounter = 0; // this is now a (static) global
-    //
-    //      uniform int gCounter; // this is now explicitly a shader parameter
-    //
-    // We skip the diagnostic whenever the variable was explicitly `uniform`,
-    // under the assumption that the programmer who added that modifier
-    // knew what they were opting into.
-    //
-    if (varDecl->hasModifier<HLSLUniformModifier>())
-        return;
-
     getSink(sharedContext)
         ->diagnose(varDecl, Diagnostics::globalUniformNotExpected, varDecl->getName());
+
+    // Check if the variable has a binding attribute
+    if (varDecl->findModifier<GLSLBindingAttribute>())
+    {
+        sharedContext->m_sink->diagnose(
+            varDecl,
+            Diagnostics::bindingAttributeIgnoredOnUniform,
+            varDecl->getName());
+    }
 }
 
 

tests/bugs/binding-attribute-ignored.slang

@@ -0,0 +1,18 @@
+// Test that binding attributes on uniforms that get packed into the default uniform buffer trigger a warning
+// GH: 4251
+// Test Vulkan binding syntax
+[[vk::binding(1, 2)]]
+uniform float4 g_position;  // This should trigger a warning since it's a uniform that will be packed
+
+[[vk::binding(3, 1)]]
+uniform float4x4 g_transform; // This should also trigger a warning
+
+// This won't trigger a warning because it's a texture (not packed into default uniform buffer)
+[[vk::binding(0, 0)]]
+Texture2D g_texture;
+
+[shader("vertex")]
+float4 main(float4 pos : POSITION) : SV_POSITION
+{
+    return g_position;
+}