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Fix C++ modules BMI installation and re-enable external build tests #7206

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2 changes: 1 addition & 1 deletion .cmake-format.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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+'}}
}

Expand Down
120 changes: 29 additions & 91 deletions cmake/HPX_CXXModules.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
# Distributed under the Boost Software License, Version 1.0. (See accompanying
# file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

include(HPX_AddCompileFlag)
include(HPX_Message)

macro(hpx_check_cxx_modules_support)
Expand Down Expand Up @@ -65,79 +64,39 @@ 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
# * Creates an interface target '<producer>_if' for consumers to link to.
# * Sets INTERFACE_CXX_SCAN_FOR_MODULES ON so that CMake's native module
# dependency tracking propagates to all consumers.
#
# CMake 3.29+ with FILE_SET CXX_MODULES handles BMI generation and
# -fmodule-output/-fprebuilt-module-path flags automatically. No manual compiler
# flags are needed here.
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()

# 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()
# Propagate scanning requirement to consumers via the interface target. CMake
# uses this to enable its native module dependency scanning for any target
# that links to this interface.
set_target_properties(${_iface} PROPERTIES INTERFACE_CXX_SCAN_FOR_MODULES ON)
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endfunction()

# hpx_configure_module_consumer(<consumer> <producer>])
# hpx_configure_module_consumer(<consumer> <producer>)
#
# * Links the consumer to the producer interface target.
# * Enables CMake's native module scanning on the consumer.
#
# * propagates module-related properties from producer interface target
# * sets necessary consumer compiler flags for clang and gcc
# CMake 3.29+ automatically resolves the BMI location from the FILE_SET
# CXX_MODULES declared on the producer. No -fprebuilt-module-path needed.
function(hpx_configure_module_consumer consumer producer)
if(NOT TARGET ${consumer})
hpx_error("hpx_configure_module_consumer: target '${consumer}' not found")
Expand All @@ -146,41 +105,20 @@ 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 ${producer} INTERFACE_CXX_SCAN_FOR_MODULES)
if(_scan)
set_target_properties(${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"
)
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()
9 changes: 4 additions & 5 deletions cmake/HPX_CollectStdHeaders.cmake
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Expand Up @@ -134,11 +134,10 @@ function(hpx_extract_includes_from_file module)
foreach(include ${includes})
string(REGEX REPLACE "#include (<[^>]+>)" "\\1" filename ${include})

if(NOT filename MATCHES "\\.|/")
# Check if the include is a standard library header
if(${filename} IN_LIST STANDARD_LIBRARY_HEADERS)
list(APPEND found_includes ${filename})
endif()
if("${filename}" IN_LIST STANDARD_LIBRARY_HEADERS)
# Capture standard library headers (with or without extensions, e.g.
# <vector>, <link.h>, <dlfcn.h>).
Comment on lines +138 to +139
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Copilot AI Apr 30, 2026

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The comment mentions capturing headers like <link.h>/<dlfcn.h>, but those are not present in STANDARD_LIBRARY_HEADERS above. As written, they will never be captured by the IN_LIST STANDARD_LIBRARY_HEADERS check. Either add the intended headers to STANDARD_LIBRARY_HEADERS (if you want them treated as “standard” for this purpose), or adjust the comment to match the actual list being checked.

Suggested change
# Capture standard library headers (with or without extensions, e.g.
# <vector>, <link.h>, <dlfcn.h>).
# Capture only headers explicitly listed in STANDARD_LIBRARY_HEADERS
# (for example, <vector>).

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@hkaiser hkaiser May 4, 2026

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This may be a valid comment to address.

list(APPEND found_includes "${filename}")
endif()
endforeach()

Expand Down
14 changes: 12 additions & 2 deletions cmake/HPX_GeneratePackage.cmake
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Expand Up @@ -19,11 +19,19 @@ write_basic_package_version_file(
COMPATIBILITY AnyNewerVersion
)

# Export HPXInternalTargets in the build directory
# CXX_MODULES_DIRECTORY was added in CMake 3.28
set(_cxx_modules_directory_arg)
if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.28")
set(_cxx_modules_directory_arg CXX_MODULES_DIRECTORY cxx-modules)
endif()
Comment on lines +22 to +26
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_cxx_modules_directory_arg is applied to the build-tree export() calls, but the corresponding install(EXPORT ...) blocks for HPXInternalTargets and HPXTargets do not pass CXX_MODULES_DIRECTORY. If install(EXPORT) is missing this argument, the installed package may not install/generate the per-target C++ module metadata directory, breaking downstream find_package(HPX) consumption of modules from an install tree. Consider forwarding the same ${_cxx_modules_directory_arg} (guarded by the same CMake version check) to both install(EXPORT ...) calls as well.

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@hkaiser hkaiser May 4, 2026

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@arpittkhandelwal Is this a valid comment?


# Export HPXInternalTargets in the build directory. Use the EXPORT signature so
# CMake also generates the per-target C++ module metadata files.
export(
TARGETS ${HPX_EXPORT_INTERNAL_TARGETS}
NAMESPACE HPXInternal::
FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXInternalTargets.cmake"
${_cxx_modules_directory_arg}
)

# Export HPXInternalTargets in the install directory
Expand All @@ -35,11 +43,13 @@ install(
COMPONENT cmake
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)

# 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 ${HPX_EXPORT_TARGETS}
NAMESPACE HPX::
FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXTargets.cmake"
${_cxx_modules_directory_arg}
)
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# Add aliases with the namespace for use within HPX
Expand Down
26 changes: 23 additions & 3 deletions cmake/HPX_SetupTarget.cmake
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Expand Up @@ -38,6 +38,7 @@ function(hpx_setup_target target)
HPX_PREFIX
HEADER_ROOT
SCAN_FOR_MODULES
CXX_STANDARD
)
set(multi_value_args DEPENDENCIES COMPONENT_DEPENDENCIES COMPILE_FLAGS
LINK_FLAGS INSTALL_FLAGS INSTALL_PDB
Expand Down Expand Up @@ -87,6 +88,13 @@ function(hpx_setup_target target)
hpx_debug("setup_target.${target}" "LINK_FLAGS: ${target_LINK_FLAGS}")
endif()

if(target_CXX_STANDARD)
set_target_properties(
${target} PROPERTIES CXX_STANDARD ${target_CXX_STANDARD}
)
hpx_debug("setup_target.${target}" "CXX_STANDARD: ${target_CXX_STANDARD}")
endif()

if(target_NAME)
set(name "${target_NAME}")
else()
Expand Down Expand Up @@ -232,9 +240,21 @@ function(hpx_setup_target target)
if(HPX_WITH_CXX_MODULES AND target_SCAN_FOR_MODULES)
hpx_debug("setup_target.${target} SCAN_FOR_MODULES: ON")

hpx_configure_module_consumer(${target} hpx_core_module_if)
if(TARGET hpx_core_module_if)
hpx_configure_module_consumer(${target} hpx_core_module_if)
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elseif(TARGET HPXInternal::hpx_core_module_if)
hpx_configure_module_consumer(${target} HPXInternal::hpx_core_module_if)
else()
hpx_error(
"setup_target.${target}: C++ modules scanning is enabled, but neither "
"hpx_core_module_if nor HPXInternal::hpx_core_module_if exists"
)
endif()

if(TARGET hpx_full_module_if)
hpx_configure_module_consumer(${target} hpx_full_module_if)
elseif(TARGET HPXInternal::hpx_full_module_if)
hpx_configure_module_consumer(${target} HPXInternal::hpx_full_module_if)
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endif()
else()
hpx_debug("setup_target.${target} SCAN_FOR_MODULES: OFF")
Expand All @@ -247,8 +267,8 @@ function(hpx_setup_target target)

# If modules are enabled, Clang emits DWARF v5, which requires using lld
# instead of ld.
if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" OR CMAKE_CXX_COMPILER_ID MATCHES
"AppleClang"
if((NOT MSVC) AND (CMAKE_CXX_COMPILER_ID MATCHES "Clang"
OR CMAKE_CXX_COMPILER_ID MATCHES "AppleClang")
)
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get_target_property(_type ${target} TYPE)
if((_type STREQUAL "SHARED_LIBRARY") OR (_type STREQUAL "EXECUTABLE"))
Expand Down
22 changes: 21 additions & 1 deletion examples/gtest_emulation/CMakeLists.txt
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Expand Up @@ -14,10 +14,23 @@ if(EXISTS "${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
add_library(static_main_lib STATIC static_main.cpp)
set_target_properties(
static_main_lib PROPERTIES CXX_STANDARD ${HPX_CXX_STANDARD}
)

# /!\ This helper interface is needed to keep the right linking order
add_library(hpx_helper_interface INTERFACE)
Expand All @@ -27,7 +40,14 @@ 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}
)
set_target_properties(
hpx_main_ext_main PROPERTIES CXX_STANDARD ${HPX_CXX_STANDARD}
)

enable_testing()
add_test(hello_world_test hpx_main_ext_main)
Expand Down
39 changes: 32 additions & 7 deletions examples/hello_world_component/CMakeLists.txt
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Expand Up @@ -11,12 +11,22 @@ project(hello_world_client CXX)
if(EXISTS "${HPX_DIR}")
find_package(HPX REQUIRED)

if(HPX_WITH_DISTRIBUTED_RUNTIME)
add_library(hello_world_component SHARED hello_world_component.cpp)
endif()

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()

if(HPX_WITH_DISTRIBUTED_RUNTIME)
add_library(hello_world_component SHARED hello_world_component.cpp)
endif()

add_executable(hello_world_client hello_world_client.cpp)
Expand All @@ -26,11 +36,15 @@ 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
Expand All @@ -44,6 +58,7 @@ 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")
Expand All @@ -53,10 +68,20 @@ if(EXISTS "${HPX_DIR}")
COMPONENT_DEPENDENCIES iostreams
DEPENDENCIES HPX::wrap_main
TYPE COMPONENT
SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES} CXX_STANDARD
${HPX_CXX_STANDARD}
)
hpx_setup_target(
hello_world_client
DEPENDENCIES hello_world_component
SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES} CXX_STANDARD
${HPX_CXX_STANDARD}
)
hpx_setup_target(hello_world_client DEPENDENCIES hello_world_component)
else()
hpx_setup_target(hello_world_client)
hpx_setup_target(
hello_world_client SCAN_FOR_MODULES ${HPX_WITH_CXX_MODULES}
CXX_STANDARD ${HPX_CXX_STANDARD}
)
endif()
else()
message(FATAL_ERROR "Unknown SETUP_TYPE=\"${SETUP_TYPE}\"")
Expand Down
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