From 652a8ee6883f08ce7cb55ef372277a535ce4d88f Mon Sep 17 00:00:00 2001
From: Copilot <198982749+Copilot@users.noreply.github.com>
Date: Tue, 15 Jul 2025 17:42:43 -0700
Subject: Add clear diagnostic for unsupported float types in generic value
 parameters (#7737)

* Initial plan

* Add validation and clear error message for float generic parameters

Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: csyonghe <2652293+csyonghe@users.noreply.github.com>
---
 source/slang/slang-check-decl.cpp                  | 12 +++++++
 source/slang/slang-diagnostic-defs.h               |  5 +++
 .../generic-value-parameter-float-type.slang       | 41 ++++++++++++++++++++++
 3 files changed, 58 insertions(+)
 create mode 100644 tests/diagnostics/generic-value-parameter-float-type.slang

diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 584b1f081..9853b0097 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -3413,6 +3413,18 @@ void SemanticsDeclHeaderVisitor::visitGenericTypeParamDecl(GenericTypeParamDecl*
 void SemanticsDeclHeaderVisitor::visitGenericValueParamDecl(GenericValueParamDecl* decl)
 {
     checkVarDeclCommon(decl);
+
+    // Validate that the type is supported for generic value parameters
+    if (decl->type.type)
+    {
+        if (!isValidCompileTimeConstantType(decl->type.type))
+        {
+            getSink()->diagnose(
+                decl,
+                Diagnostics::genericValueParameterTypeNotSupported,
+                decl->type.type);
+        }
+    }
 }
 
 void SemanticsDeclHeaderVisitor::visitGenericDecl(GenericDecl* genericDecl)
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index fdfa968c3..c549ccca3 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -1704,6 +1704,11 @@ DIAGNOSTIC(
     Error,
     genericValueParameterMustHaveType,
     "a generic value parameter must be given an explicit type")
+DIAGNOSTIC(
+    30624,
+    Error,
+    genericValueParameterTypeNotSupported,
+    "generic value parameter type '$0' is not supported; only integer and enum types are allowed")
 
 // 307xx: parameters
 DIAGNOSTIC(
diff --git a/tests/diagnostics/generic-value-parameter-float-type.slang b/tests/diagnostics/generic-value-parameter-float-type.slang
new file mode 100644
index 000000000..0f9cde255
--- /dev/null
+++ b/tests/diagnostics/generic-value-parameter-float-type.slang
@@ -0,0 +1,41 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+// Test that generic value parameters with float types are properly rejected
+
+// CHECK: error 30624: generic value parameter type 'float' is not supported
+struct ColorDefiner<let TMult : float>
+{
+    float4 color = {0.3, 0.7, 0.55, 1.0};
+
+    float4 get_color() { return color * TMult; }
+}
+
+// CHECK: error 30624: generic value parameter type 'double' is not supported
+struct DoubleDefiner<let TMult : double>
+{
+    float4 color = {0.3, 0.7, 0.55, 1.0};
+
+    float4 get_color() { return color * float(TMult); }
+}
+
+// Integer types should work fine (no error expected)
+struct IntDefiner<let TMult : int>
+{
+    float4 color = {0.3, 0.7, 0.55, 1.0};
+
+    float4 get_color() { return color * TMult; }
+}
+
+// Enum types should work fine (no error expected)
+enum Color { Red = 1, Green = 2, Blue = 3 }
+
+struct EnumDefiner<let TMult : Color>
+{
+    float4 color = {0.3, 0.7, 0.55, 1.0};
+
+    float4 get_color() { return color * int(TMult); }
+}
+
+void computeMain()
+{
+}
\ No newline at end of file
-- 
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