From db24484e47ce0d226300c189146c62600ccb8f2f Mon Sep 17 00:00:00 2001
From: "Larsen, Steffen" <steffen.larsen@intel.com>
Date: Thu, 26 Jun 2025 22:40:23 -0700
Subject: [PATCH] [SYCL] Add workaround for undeterminable constexpr lambda
 return

Due to a bug in the compiler, certain conditions give false compiler
errors for return types of constexpr lambdas. This commit implements
workarounds for cases that affect the SYCL headers when using
properties.

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>
---
 .../sycl/ext/oneapi/properties/properties.hpp     |  4 ++--
 .../sycl/ext/oneapi/properties/property.hpp       |  2 +-
 sycl/test/regression/grf_properties_wa.cpp        | 15 +++++++++++++++
 3 files changed, 18 insertions(+), 3 deletions(-)
 create mode 100644 sycl/test/regression/grf_properties_wa.cpp

diff --git a/sycl/include/sycl/ext/oneapi/properties/properties.hpp b/sycl/include/sycl/ext/oneapi/properties/properties.hpp
index 354975b857d13..4d3e11ec8b143 100644
--- a/sycl/include/sycl/ext/oneapi/properties/properties.hpp
+++ b/sycl/include/sycl/ext/oneapi/properties/properties.hpp
@@ -48,7 +48,7 @@ using properties_t =
     properties<detail::properties_type_list<PropertyValueTs...>>;
 
 template <typename... property_tys>
-inline constexpr bool properties_are_unique = []() constexpr {
+inline constexpr bool properties_are_unique = []() constexpr -> bool {
   if constexpr (sizeof...(property_tys) == 0) {
     return true;
   } else {
@@ -64,7 +64,7 @@ inline constexpr bool properties_are_unique = []() constexpr {
 }();
 
 template <typename... property_tys>
-inline constexpr bool properties_are_sorted = []() constexpr {
+inline constexpr bool properties_are_sorted = []() constexpr -> bool {
   if constexpr (sizeof...(property_tys) == 0) {
     return true;
   } else {
diff --git a/sycl/include/sycl/ext/oneapi/properties/property.hpp b/sycl/include/sycl/ext/oneapi/properties/property.hpp
index 37e1777e21235..d68ec8884d93b 100644
--- a/sycl/include/sycl/ext/oneapi/properties/property.hpp
+++ b/sycl/include/sycl/ext/oneapi/properties/property.hpp
@@ -258,7 +258,7 @@ struct property_base : property_key_tag<property_key_t> {
   // Temporary, to ensure new code matches previous behavior and to catch any
   // silly copy-paste mistakes. MSVC can't compile it, but linux-only is
   // enough for this temporary check.
-  static_assert([]() constexpr {
+  static_assert([]() constexpr -> bool {
     if constexpr (std::is_same_v<property_t, key_t>)
       // key_t is incomplete at this point for runtime properties.
       return true;
diff --git a/sycl/test/regression/grf_properties_wa.cpp b/sycl/test/regression/grf_properties_wa.cpp
new file mode 100644
index 0000000000000..5bce42a25734a
--- /dev/null
+++ b/sycl/test/regression/grf_properties_wa.cpp
@@ -0,0 +1,15 @@
+// RUN: %clangxx -fsycl -fsyntax-only %s
+
+// Test for a workaround to a bug in clang causing some constexpr lambda
+// expressions to not be identified as returning a bool.
+
+#include <sycl/detail/kernel_properties.hpp>
+#include <sycl/ext/intel/experimental/grf_size_properties.hpp>
+#include <sycl/sycl.hpp>
+
+int main() {
+  if constexpr (false) {
+    sycl::ext::oneapi::experimental::properties prop{
+        sycl::ext::intel::experimental::grf_size<256>};
+  }
+}