Fix C++ module installation for downstream BMI discovery

Author: arpittkhandelwal

.cmake-format.py

@@ -586,7 +586,7 @@
                                                     'INCLUDE_DIRS': '+',
                                                     'FOUND_HEADERS': 1},
                           'pargs': { 'flags': [], 'nargs': '1+'}},
-    'hpx_configure_module_producer': { 'kwargs': { 'MODULE_OUT_DIR': 1},
+    'hpx_configure_module_producer': { 'kwargs': {},
                           'pargs': { 'flags': [], 'nargs': '1+'}}
   }
 

cmake/HPX_CXXModules.cmake

@@ -65,73 +65,23 @@ 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
+  # Make sure consumers scan for modules through CMake's native module handling
   set_target_properties(${_iface} PROPERTIES INTERFACE_CXX_SCAN_FOR_MODULES On)
-
-  if(MSVC)
-    # MSVC: CMake/MSVC handle IFCs automatically; create a target for
-    # convenience, consumers can link to this to get ordering and include info
-    return()
-  endif()
-
-  # Compiler-specific flags to instruct where to write module cache
-  if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES
-                                              "AppleClang"
-  )
-    # Clang common flags
-    target_compile_options(${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()
 endfunction()
 
 # hpx_configure_module_consumer(<consumer> <producer>])
@@ -150,37 +100,15 @@ 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()

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

@@ -10,12 +10,6 @@ if(NOT HPX_WITH_TESTS_EXTERNAL_BUILD)
   return()
 endif()
 
-# If C++ modules are enabled, exit now (we don't know yet how to setup a
-# dependent HPX project to use the generated BMIs).
-if(HPX_WITH_CXX_MODULES)
-  return()
-endif()
-
 # Try building an external cmake based project ...
 function(
   create_cmake_test