5 files changed, 42 insertions, 0 deletions
diff --git a/source/slang/slang-check-conformance.cpp b/source/slang/slang-check-conformance.cpp
index d6e73e798..ff4a40031 100644
--- a/source/slang/slang-check-conformance.cpp
+++ b/source/slang/slang-check-conformance.cpp
@@ -237,6 +237,15 @@ namespace Slang
         return false;
     }
 
+    bool SemanticsVisitor::isValidGenericConstraintType(Type* type)
+    {
+        if (auto andType = as<AndType>(type))
+        {
+            return isValidGenericConstraintType(andType->getLeft()) && isValidGenericConstraintType(andType->getRight());
+        }
+        return isInterfaceType(type);
+    }
+
     bool SemanticsVisitor::isTypeDifferentiable(Type* type)
     {
         return isSubtype(type, m_astBuilder->getDiffInterfaceType());
diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index c08e8f7ef..88a707ed8 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -2206,6 +2206,10 @@ namespace Slang
         CheckConstraintSubType(decl->sub);
         decl->sub = TranslateTypeNodeForced(decl->sub);
         decl->sup = TranslateTypeNodeForced(decl->sup);
+        if (!isValidGenericConstraintType(decl->sup) && !as<ErrorType>(decl->sub.type))
+        {
+            getSink()->diagnose(decl->sup.exp, Diagnostics::invalidTypeForConstraint, decl->sup);
+        }
     }
 
     void SemanticsDeclHeaderVisitor::visitGenericTypeParamDecl(GenericTypeParamDecl* decl)
diff --git a/source/slang/slang-check-impl.h b/source/slang/slang-check-impl.h
index b1618dfb6..28c145498 100644
--- a/source/slang/slang-check-impl.h
+++ b/source/slang/slang-check-impl.h
@@ -2017,6 +2017,7 @@ namespace Slang
         SubtypeWitness* checkAndConstructSubtypeWitness(Type* subType, Type* superType);
 
         bool isInterfaceType(Type* type);
+        bool isValidGenericConstraintType(Type* type);
 
         bool isTypeDifferentiable(Type* type);
 
diff --git a/source/slang/slang-diagnostic-defs.h b/source/slang/slang-diagnostic-defs.h
index 8df51211a..5b66a0f91 100644
--- a/source/slang/slang-diagnostic-defs.h
+++ b/source/slang/slang-diagnostic-defs.h
@@ -476,6 +476,7 @@ DIAGNOSTIC(39901, Fatal , cannotProcessInclude, "internal compiler error: cannot
 
 // 304xx: generics
 DIAGNOSTIC(30400, Error, genericTypeNeedsArgs, "generic type '$0' used without argument")
+DIAGNOSTIC(30401, Error, invalidTypeForConstraint, "type '$0' cannot be used as a constraint.")
 
 // 305xx: initializer lists
 DIAGNOSTIC(30500, Error, tooManyInitializers, "too many initializers (expected $0, got $1)")
diff --git a/tests/diagnostics/invalid-constraint.slang b/tests/diagnostics/invalid-constraint.slang
new file mode 100644
index 000000000..667077ffb
--- /dev/null
+++ b/tests/diagnostics/invalid-constraint.slang
@@ -0,0 +1,27 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK):
+
+interface IFoo
+{
+    This foo();
+}
+
+struct Foo : IFoo
+{
+    float x;
+    This foo()
+    {
+        This f;
+        f.x = 0.0;
+        return f;
+    }
+}
+
+RWStructuredBuffer<float> output;
+
+// CHECK: ([[# @LINE+1]]): error 30401
+float compute<T:Foo>(T f) // error, should be IFoo here.
+{
+}
+
+void main()
+{}