[clang][SYCL] Print canonical types in free function shim functions (#16119)

Somehow even if the outer type was canonical, TypePrinter manages to
skip nns printing in case of nested default template arguments. See
added test case for the example.

Author: Fznamznon

clang/lib/Sema/SemaSYCL.cpp

@@ -6510,6 +6510,7 @@ void SYCLIntegrationHeader::emit(raw_ostream &O) {
     std::string ParmList;
     bool FirstParam = true;
     Policy.SuppressDefaultTemplateArgs = false;
+    Policy.PrintCanonicalTypes = true;
     for (ParmVarDecl *Param : K.SyclKernel->parameters()) {
       if (FirstParam)
         FirstParam = false;
@@ -6518,6 +6519,7 @@ void SYCLIntegrationHeader::emit(raw_ostream &O) {
       ParmList += Param->getType().getCanonicalType().getAsString(Policy);
     }
     FunctionTemplateDecl *FTD = K.SyclKernel->getPrimaryTemplate();
+    Policy.PrintCanonicalTypes = false;
     Policy.SuppressDefinition = true;
     Policy.PolishForDeclaration = true;
     Policy.FullyQualifiedName = true;

clang/test/CodeGenSYCL/free_function_default_template_arguments.cpp

@@ -60,6 +60,24 @@ templated3(Arg<T, notatuple, a, ns1::hasDefaultArg<>, int, int>, T end) {
 
 template void templated3(Arg<int, notatuple, 3, ns1::hasDefaultArg<>, int, int>, int);
 
+
+namespace sycl {
+template <typename T> struct X {};
+template <> struct X<int> {};
+namespace detail {
+struct Y {};
+} // namespace detail
+template <> struct X<detail::Y> {};
+} // namespace sycl
+using namespace sycl;
+template <typename T, typename = X<detail::Y>> struct Arg1 { T val; };
+
+[[__sycl_detail__::add_ir_attributes_function("sycl-single-task-kernel",
+                                              2)]] void
+foo(Arg1<int> arg) {
+  arg.val = 42;
+}
+
 // CHECK: Forward declarations of kernel and its argument types:
 // CHECK-NEXT: namespace ns { 
 // CHECK-NEXT: struct notatuple;
@@ -98,3 +116,17 @@ template void templated3(Arg<int, notatuple, 3, ns1::hasDefaultArg<>, int, int>,
 // CHECK-NEXT: static constexpr auto __sycl_shim5() {
 // CHECK-NEXT:   return (void (*)(struct ns::Arg<int, struct ns::notatuple, 3, class ns::ns1::hasDefaultArg<struct ns::notatuple>, int, int>, int))templated3<int, 3>;
 // CHECK-NEXT: }
+
+// CHECK Forward declarations of kernel and its argument types:
+// CHECK: namespace sycl { namespace detail {
+// CHECK-NEXT: struct Y;
+// CHECK-NEXT: }}
+// CHECK-NEXT: namespace sycl {
+// CHECK-NEXT: template <typename T> struct X;
+// CHECK-NEXT: }
+// CHECK-NEXT: template <typename T, typename> struct Arg1;
+
+// CHECK: void foo(Arg1<int, sycl::X<sycl::detail::Y> > arg);
+// CHECK-NEXT: static constexpr auto __sycl_shim6() {
+// CHECK-NEXT:   return (void (*)(struct Arg1<int, struct sycl::X<struct sycl::detail::Y> >))foo;
+// CHECK-NEXT: }