Address reviewer feedback: Refine module dependencies and fix circularity

Author: arpittkhandelwal

cmake/HPX_CXXModules.cmake

@@ -65,73 +65,27 @@ if(NOT HPX_WITH_CXX_MODULES)
   return()
 endif()
 
-# hpx_configure_module_producer(<producer> [MODULE_OUT_DIR <dir>])
+# hpx_configure_module_producer(<producer>)
 #
-# * Ensures a stable module output dir for producer target
-# * Adds compiler flags to write module cache there (Clang/GCC)
 # * Creates an interface target '<producer>_if' for consumers to link to
+# * Marks the interface target for CMake's native module scanning
 function(hpx_configure_module_producer producer)
   if(NOT TARGET ${producer})
     hpx_error("hpx_configure_module_producer: target '${producer}' not found")
   endif()
 
-  # parse optional args
-  set(options)
-  set(one_value_args MODULE_OUT_DIR)
-  set(multi_value_args)
-  cmake_parse_arguments(
-    _args "${options}" "${one_value_args}" "${multi_value_args}" ${ARGN}
-  )
-
-  if(_args_MODULE_OUT_DIR)
-    set(_moddir "${_args_MODULE_OUT_DIR}")
-  else()
-    set(_moddir "$<TARGET_FILE_DIR:${producer}>")
-  endif()
-
   set(_iface "${producer}_if")
   if(NOT TARGET ${_iface})
     add_library(${_iface} INTERFACE)
     target_link_libraries(${_iface} INTERFACE ${producer})
   endif()
 
-  # Set a property so consumers can query the BMI directory via
-  # get_target_property.
-  set_target_properties(
-    ${_iface} PROPERTIES INTERFACE_EXPORT_MODULE_DIR "${_moddir}"
-  )
-
-  # Make sure consumers scan for the BMI
-  set_target_properties(${_iface} PROPERTIES INTERFACE_CXX_SCAN_FOR_MODULES On)
-
-  if(MSVC)
-    # MSVC: CMake/MSVC handle IFCs automatically; create a target for
-    # convenience, consumers can link to this to get ordering and include info
-    return()
-  endif()
+  # Make sure consumers scan for modules through CMake's native module handling
+  set_target_properties(${_iface} PROPERTIES INTERFACE_CXX_SCAN_FOR_MODULES ON)
 
-  # Compiler-specific flags to instruct where to write module cache
-  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES
-                                              "AppleClang"
-  )
-    # Clang common flags
-    target_compile_options(${producer} PRIVATE "-fmodule-output=${_moddir}")
-  elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    # GCC: modern flags
-    hpx_add_target_compile_option_if_available(
-      ${producer} PRIVATE "-fmodule-output=${_moddir}" RESULT ok
-    )
-    if(NOT ok)
-      hpx_error(
-        "hpx_configure_module_producer: the used version of gcc does not support '-fmodule-output'"
-      )
-    endif()
-  else()
-    hpx_warn(
-      "hpx_configure_module_producer: unknown compiler '${CMAKE_CXX_COMPILER_ID}'; "
-      "exposing EXPORT_MODULE_DIR='${_moddir}' for manual handling"
-    )
-  endif()
+  # Define HPX_COMPILE_BMI to ensure that internal headers use #include instead
+  # of import during the generation of the BMI.
+  target_compile_definitions(${producer} PRIVATE HPX_COMPILE_BMI)
 endfunction()
 
 # hpx_configure_module_consumer(<consumer> <producer>])
@@ -150,37 +104,15 @@ function(hpx_configure_module_consumer consumer producer)
   get_target_property(_scan ${producer} INTERFACE_CXX_SCAN_FOR_MODULES)
   if(_scan)
     set_target_properties(${consumer} PROPERTIES CXX_SCAN_FOR_MODULES ${_scan})
-  endif()
 
-  get_target_property(_module_dir ${producer} INTERFACE_EXPORT_MODULE_DIR)
-  if(_module_dir)
-    if(MSVC)
-      return()
-    elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID
-                                                    MATCHES "AppleClang"
+    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES
+                                                "AppleClang"
     )
-      target_compile_options(
-        ${consumer} PRIVATE "-fprebuilt-module-path=${_module_dir}"
-      )
       get_target_property(_type ${consumer} TYPE)
       if((_type STREQUAL "SHARED_LIBRARY") OR (_type STREQUAL "EXECUTABLE"))
         target_link_options(${consumer} PRIVATE "-fuse-ld=lld")
         target_link_options(${consumer} PRIVATE "-Wl,--error-limit=0")
       endif()
-    elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-      hpx_add_target_compile_option_if_available(
-        ${consumer} PRIVATE "-fprebuilt-module-path=${_module_dir}" RESULT ok
-      )
-      if(NOT ok)
-        hpx_error(
-          "hpx_configure_module_consumer: the used version of gcc does not "
-          "support '-fprebuilt-module-path='"
-        )
-      endif()
-    else()
-      hpx_warn(
-        "hpx_configure_module_consumer: unknown compiler '${CMAKE_CXX_COMPILER_ID}'"
-      )
     endif()
   endif()
 endfunction()

examples/hello_world_component/CMakeLists.txt

@@ -31,25 +31,6 @@ if(EXISTS "${HPX_DIR}")
       target_link_libraries(hello_world_client PRIVATE hello_world_component)
     endif()
     target_link_libraries(hello_world_client PRIVATE HPX::hpx HPX::wrap_main)
-    if(HPX_WITH_CXX_MODULES)
-      if(TARGET hpx_core_module_if)
-        if(TARGET hello_world_component)
-          target_link_libraries(
-            hello_world_component PRIVATE hpx_core_module_if
-          )
-        endif()
-        target_link_libraries(hello_world_client PRIVATE hpx_core_module_if)
-      elseif(TARGET HPXInternal::hpx_core_module_if)
-        if(TARGET hello_world_component)
-          target_link_libraries(
-            hello_world_component PRIVATE HPXInternal::hpx_core_module_if
-          )
-        endif()
-        target_link_libraries(
-          hello_world_client PRIVATE HPXInternal::hpx_core_module_if
-        )
-      endif()
-    endif()
 
     # 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
@@ -72,15 +53,17 @@ if(EXISTS "${HPX_DIR}")
         COMPONENT_DEPENDENCIES iostreams
         DEPENDENCIES HPX::wrap_main
         TYPE COMPONENT
-        SCAN_FOR_MODULES ON
+        SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES}
       )
       hpx_setup_target(
         hello_world_client
         DEPENDENCIES hello_world_component
-        SCAN_FOR_MODULES ON
+        SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES}
       )
     else()
-      hpx_setup_target(hello_world_client SCAN_FOR_MODULES ON)
+      hpx_setup_target(
+        hello_world_client SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES}
+      )
     endif()
   else()
     message(FATAL_ERROR "Unknown SETUP_TYPE=\"${SETUP_TYPE}\"")

libs/CMakeLists.txt

@@ -342,10 +342,7 @@ foreach(lib ${HPX_LIBS})
     set_target_properties(
       hpx_${lib}_module PROPERTIES POSITION_INDEPENDENT_CODE ON
     )
-    hpx_configure_module_producer(
-      hpx_${lib}_module MODULE_OUT_DIR
-      ${CMAKE_INSTALL_LIBDIR}/cmake/${HPX_PACKAGE_NAME}/${lib}
-    )
+    hpx_configure_module_producer(hpx_${lib}_module)
 
     target_link_libraries(
       hpx_${lib}_module

tests/unit/build/CMakeLists.txt

@@ -73,14 +73,7 @@ function(
     VERBATIM
   )
   add_dependencies(${name} hpx hpx_init hpx_wrap)
-  if(HPX_WITH_CXX_MODULES)
-    if(TARGET hpx_core_module)
-      add_dependencies(${name} hpx_core_module)
-    endif()
-    if(TARGET hpx_full_module)
-      add_dependencies(${name} hpx_full_module)
-    endif()
-  endif()
+
   if(HPX_WITH_DISTRIBUTED_RUNTIME)
     add_dependencies(${name} iostreams_component)
   endif()