Improve diagnotic messages

Author: Fznamznon

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12414,6 +12414,14 @@ def err_sycl_kernel_incorrectly_named : Error<
   "'-fsycl-unnamed-lambda' to enable unnamed kernel lambdas"
   "}0">;
 
+// SYCL free function kernels extension.
+def err_bad_free_function_kernel_param_type : Error<
+  "%0 cannot be used as the type of a free function kernel parameter">;
+def note_free_function_kernel_param_type_not_fwd_declarable : Note<
+  "%0 is not forward declarable">;
+def note_free_function_kernel_param_type_not_supported : Note<
+  "%0 is not yet supported as free function kernel parameter">;
+
 def err_sycl_kernel_not_function_object
     : Error<"kernel parameter must be a lambda or function object">;
 def err_sycl_restrict : Error<

clang/lib/Sema/SemaSYCL.cpp

@@ -1966,7 +1966,11 @@ class SyclKernelFieldChecker : public SyclKernelFieldHandler {
     // arguments.
     // Lambdas are not forward declarable. So, diagnose them properly.
     if (RD->isLambda()) {
-      Diag.Report(PD->getLocation(), diag::err_bad_kernel_param_type)
+      Diag.Report(PD->getLocation(),
+                  diag::err_bad_free_function_kernel_param_type)
+          << ParamTy;
+      Diag.Report(PD->getLocation(),
+                  diag::note_free_function_kernel_param_type_not_fwd_declarable)
           << ParamTy;
       IsInvalid = true;
       return isValid();
@@ -1979,7 +1983,11 @@ class SyclKernelFieldChecker : public SyclKernelFieldHandler {
       DeclCtx = DeclCtx->getParent();
 
     if (!DeclCtx->isTranslationUnit()) {
-      Diag.Report(PD->getLocation(), diag::err_bad_kernel_param_type)
+      Diag.Report(PD->getLocation(),
+                  diag::err_bad_free_function_kernel_param_type)
+          << ParamTy;
+      Diag.Report(PD->getLocation(),
+                  diag::note_free_function_kernel_param_type_not_fwd_declarable)
           << ParamTy;
       IsInvalid = true;
     }
@@ -2077,7 +2085,11 @@ class SyclKernelFieldChecker : public SyclKernelFieldHandler {
     // experience.
     CXXRecordDecl *RD = ParamTy->getAsCXXRecordDecl();
     if (RD->hasAttr<SYCLRequiresDecompositionAttr>()) {
-      Diag.Report(PD->getLocation(), diag::err_bad_kernel_param_type)
+      Diag.Report(PD->getLocation(),
+                  diag::err_bad_free_function_kernel_param_type)
+          << ParamTy;
+      Diag.Report(PD->getLocation(),
+                  diag::note_free_function_kernel_param_type_not_supported)
           << ParamTy;
       IsInvalid = true;
     }

clang/test/SemaSYCL/free_function_kernel_params_restrictions.cpp

@@ -13,13 +13,15 @@ class Outer {
 
 __attribute__((sycl_device))
 [[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 0)]]
-void ff_4(Outer::DefinedWithinAClass S1) { // expected-error {{'Outer::DefinedWithinAClass' cannot be used as the type of a kernel parameter}}
+void ff_4(Outer::DefinedWithinAClass S1) { // expected-error {{'Outer::DefinedWithinAClass' cannot be used as the type of a free function kernel parameter}}
+                                           // expected-note@-1 {{'Outer::DefinedWithinAClass' is not forward declarable}}
 }
 
 template <typename T1>
 __attribute__((sycl_device))
 [[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 0)]]
-  void ff_6(T1 S1) { // expected-error 2{{cannot be used as the type of a kernel parameter}}
+  void ff_6(T1 S1) { // expected-error 2{{cannot be used as the type of a free function kernel parameter}}
+                     // expected-note@-1 2{{is not forward declarable}}
 }
 
 void bar() {
@@ -54,5 +56,6 @@ struct Wrapper {
 };
 
 [[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel", 0)]]
-void ff_6(Wrapper S1) { // expected-error {{cannot be used as the type of a kernel parameter}}
+void ff_6(Wrapper S1) { // expected-error {{cannot be used as the type of a free function kernel parameter}}
+                        // expected-note@-1 {{'Wrapper' is not yet supported as free function kernel parameter}}
 }