Add Stdexec to the build system (will be formalized later)

CMakeLists.txt

@@ -2196,6 +2196,9 @@ include(HPX_SetupAsio)
 include(HPX_SetupAllocator)
 include(HPX_SetupHwloc)
 
+# Setup NVIDIA's stdexec
+include(HPX_SetupStdexec)
+
 # reset external source lists
 add_hpx_library_sources_noglob(hpx_external)
 add_hpx_library_headers_noglob(hpx_external)

cmake/FindStdexec.cmake

@@ -0,0 +1,29 @@
+
+if(NOT TARGET STDEXEC::stdexec)
+  # print out STDEXEC_ROOT
+    message(STATUS "Stdexec_ROOT: ${Stdexec_ROOT}")
+    set(Stdexec_ROOT ${Stdexec_ROOT})
+
+    find_path(
+      Stdexec_INCLUDE_DIR stdexec
+      HINTS "${Stdexec_ROOT}" ENV STDEXEC_ROOT
+      PATH_SUFFIXES include
+    )
+
+    if (NOT Stdexec_INCLUDE_DIR)
+      message(FATAL_ERROR "stdexec not found")
+    endif()
+
+    add_library(STDEXEC::stdexec INTERFACE IMPORTED)
+    target_include_directories(STDEXEC::stdexec INTERFACE ${Stdexec_INCLUDE_DIR})
+
+    include(FindPackageHandleStandardArgs)
+    find_package_handle_standard_args(
+        Stdexec
+        REQUIRED_VARS Stdexec_INCLUDE_DIR
+        VERSION_VAR "1.0"
+        FOUND_VAR Stdexec_FOUND
+    )
+
+    mark_as_advanced(Stdexec_INCLUDE_DIR Stdexec_ROOT)
+endif()

cmake/HPX_SetupStdexec.cmake

@@ -0,0 +1,17 @@
+
+
+if(STDEXEC_ROOT AND NOT Stdexec_ROOT)
+  set(Stdexec_ROOT
+      ${STDEXEC_ROOT}
+      CACHE PATH "STDEXEC base directory"
+  )
+  unset(STDEXEC_ROOT CACHE)
+endif()
+
+find_package(Stdexec REQUIRED)
+
+if(NOT Stdexec_FOUND)
+    hpx_error(
+        "Stdexec could not be found, please specify Stdexec_ROOT to point to the correct location"
+    )
+endif()