Fix external C++ modules package consumers

Author: LSUDOKO

cmake/HPX_CXXModules.cmake

@@ -116,6 +116,16 @@ function(hpx_configure_module_consumer consumer producer)
     hpx_error("hpx_configure_module_consumer: target '${producer}' not found")
   endif()
 
+  # Imported module metadata is only picked up from direct link dependencies.
+  # Link the underlying module target directly when the producer follows the
+  # '<module>_if' wrapper pattern.
+  if(producer MATCHES "_if$")
+    string(REGEX REPLACE "_if$" "" _producer_target "${producer}")
+    if(TARGET ${_producer_target})
+      target_link_libraries(${consumer} PRIVATE ${_producer_target})
+    endif()
+  endif()
+
   target_link_libraries(${consumer} PRIVATE ${producer})
   get_target_property(_scan ${producer} INTERFACE_CXX_SCAN_FOR_MODULES)
   if(_scan)

cmake/HPX_GeneratePackage.cmake

@@ -19,11 +19,13 @@ write_basic_package_version_file(
   COMPATIBILITY AnyNewerVersion
 )
 
-# Export HPXInternalTargets in the build directory
+# Export HPXInternalTargets in the build directory. Use the EXPORT
+# signature so CMake also generates the per-target C++ module metadata files.
 export(
-  TARGETS ${HPX_EXPORT_INTERNAL_TARGETS}
+  EXPORT HPXInternalTargets
   NAMESPACE HPXInternal::
   FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXInternalTargets.cmake"
+  CXX_MODULES_DIRECTORY cxx-modules
 )
 
 # Export HPXInternalTargets in the install directory
@@ -32,14 +34,17 @@ install(
   NAMESPACE HPXInternal::
   FILE HPXInternalTargets.cmake
   DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${HPX_PACKAGE_NAME}
+  CXX_MODULES_DIRECTORY cxx-modules
   COMPONENT cmake
 )
 
-# Export HPXTargets in the build directory
+# Export HPXTargets in the build directory. Use the EXPORT signature so
+# CMake also generates the per-target C++ module metadata files.
 export(
-  TARGETS ${HPX_EXPORT_TARGETS}
+  EXPORT HPXTargets
   NAMESPACE HPX::
   FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXTargets.cmake"
+  CXX_MODULES_DIRECTORY cxx-modules
 )
 
 # Add aliases with the namespace for use within HPX
@@ -57,6 +62,7 @@ install(
   NAMESPACE HPX::
   FILE HPXTargets.cmake
   DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${HPX_PACKAGE_NAME}
+  CXX_MODULES_DIRECTORY cxx-modules
   COMPONENT cmake
 )
 

examples/gtest_emulation/CMakeLists.txt

@@ -14,6 +14,17 @@ if(EXISTS "${HPX_DIR}")
 
   if(HPX_WITH_CXX_MODULES)
     set(CMAKE_CXX_SCAN_FOR_MODULES ON)
+
+    # CMake only propagates imported C++ module metadata from targets that are
+    # linked directly by the consumer. The exported HPXInternal module targets
+    # are therefore linked explicitly for the external build tests.
+    set(hpx_cxx_module_targets)
+    if(TARGET HPXInternal::hpx_core_module)
+      list(APPEND hpx_cxx_module_targets HPXInternal::hpx_core_module)
+    endif()
+    if(TARGET HPXInternal::hpx_full_module)
+      list(APPEND hpx_cxx_module_targets HPXInternal::hpx_full_module)
+    endif()
   endif()
 
   # Add a static library which contains a main to emulate gtest_main
@@ -27,7 +38,11 @@ if(EXISTS "${HPX_DIR}")
 
   # Test with the main function in a separate static library
   add_executable(hpx_main_ext_main hpx_main_ext_main.cpp)
-  target_link_libraries(hpx_main_ext_main PRIVATE hpx_helper_interface)
+  # Keep the helper interface for link order, but link module targets directly
+  # to the executable so CMake can see the imported BMI metadata.
+  target_link_libraries(
+    hpx_main_ext_main PRIVATE hpx_helper_interface ${hpx_cxx_module_targets}
+  )
 
   enable_testing()
   add_test(hello_world_test hpx_main_ext_main)

examples/hello_world_component/CMakeLists.txt

@@ -17,6 +17,17 @@ if(EXISTS "${HPX_DIR}")
 
   if(HPX_WITH_CXX_MODULES)
     set(CMAKE_CXX_SCAN_FOR_MODULES ON)
+
+    # CMake only propagates imported C++ module metadata from targets that are
+    # linked directly by the consumer. The exported HPXInternal module targets
+    # are therefore linked explicitly for the external build tests.
+    set(hpx_cxx_module_targets)
+    if(TARGET HPXInternal::hpx_core_module)
+      list(APPEND hpx_cxx_module_targets HPXInternal::hpx_core_module)
+    endif()
+    if(TARGET HPXInternal::hpx_full_module)
+      list(APPEND hpx_cxx_module_targets HPXInternal::hpx_full_module)
+    endif()
   endif()
 
   add_executable(hello_world_client hello_world_client.cpp)
@@ -26,11 +37,15 @@ if(EXISTS "${HPX_DIR}")
     if(HPX_WITH_DISTRIBUTED_RUNTIME)
       target_link_libraries(
         hello_world_component PUBLIC HPX::hpx HPX::iostreams_component
+                                     ${hpx_cxx_module_targets}
       )
       target_link_libraries(hello_world_component PRIVATE HPX::component)
       target_link_libraries(hello_world_client PRIVATE hello_world_component)
     endif()
-    target_link_libraries(hello_world_client PRIVATE HPX::hpx HPX::wrap_main)
+    target_link_libraries(
+      hello_world_client PRIVATE HPX::hpx HPX::wrap_main
+                                ${hpx_cxx_module_targets}
+    )
 
     # We still support not linking to HPX::wrap_main when
     # HPX_WITH_DYNAMIC_HPX_MAIN=OFF for legacy use. This can only be done using
@@ -44,6 +59,7 @@ if(EXISTS "${HPX_DIR}")
 
       target_link_libraries(
         hello_world_client_only_hpx_init PRIVATE hello_world_component
+                                                 ${hpx_cxx_module_targets}
       )
     endif()
   elseif("${SETUP_TYPE}" STREQUAL "MACROS")