From: Felix W. (65278) <felix@zeynix.de> 
Date: Fri, 11 Sep 2026 15:30:00 +0200
Subject: [PATCH] cmake: add clang/libcxx experimental features for object_io_exerciser

object_io_exerciser uses std::execution, which is an experimental
feature in libcxx. This patch adds -fexperimental-library should
the symbol std::execution::seq not exist if you're using clang.
This possibly breaks on win32, but I have no way of testing.

Index: ceph-20.2.4/src/common/io_exerciser/CMakeLists.txt
===================================================================
--- ceph-20.2.4.orig/src/common/io_exerciser/CMakeLists.txt
+++ ceph-20.2.4/src/common/io_exerciser/CMakeLists.txt
@@ -26,3 +26,17 @@ if(TBB_FOUND)
   message(STATUS "Linking to TBB for implementations of <execution>.")
   target_link_libraries(object_io_exerciser TBB::tbb)
 endif(TBB_FOUND)
+
+
+# libcxx std::execution is experimental. If compiling with clang++
+# and the symbol std::execution::seq does not exist, we set 
+# -fexperimental-library to set _LIBCPP_HAS_EXPERIMENTAL_PSTL:
+# https://github.com/llvm/llvm-project/blob/llvmorg-22.1.8/libcxx/include/execution#L48
+include(CheckCXXSymbolExists)
+check_cxx_symbol_exists("std::execution::seq" execution HAVE_EXECUTION_SEQ)
+
+if((NOT HAVE_EXECUTION_SEQ) AND (CMAKE_CXX_COMPILER_ID STREQUAL "Clang"))
+  target_compile_options(object_io_exerciser 
+	  PRIVATE "-fexperimental-library"
+  ) 
+endif()