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Rework Modules CMake to be (more) idiomatic. #84936

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Mar 15, 2024
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29 changes: 2 additions & 27 deletions libcxx/docs/Modules.rst
Original file line number Diff line number Diff line change
Expand Up @@ -178,34 +178,13 @@ This is a small sample program that uses the module ``std``. It consists of a
)
FetchContent_MakeAvailable(std)

#
# Adjust project compiler flags
#

add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fprebuilt-module-path=${std_BINARY_DIR}/CMakeFiles/std.dir/>)
add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fprebuilt-module-path=${std_BINARY_DIR}/CMakeFiles/std.compat.dir/>)
add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-nostdinc++>)
# The include path needs to be set to be able to use macros from headers.
# For example from, the headers <cassert> and <version>.
add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-isystem>)
add_compile_options($<$<COMPILE_LANGUAGE:CXX>:${LIBCXX_BUILD}/include/c++/v1>)

#
# Adjust project linker flags
#

add_link_options($<$<COMPILE_LANGUAGE:CXX>:-nostdlib++>)
add_link_options($<$<COMPILE_LANGUAGE:CXX>:-L${LIBCXX_BUILD}/lib>)
add_link_options($<$<COMPILE_LANGUAGE:CXX>:-Wl,-rpath,${LIBCXX_BUILD}/lib>)
# Linking against the standard c++ library is required for CMake to get the proper dependencies.
link_libraries(std c++)
link_libraries(std.compat c++)

#
# Add the project
#

add_executable(main)
add_dependencies(main std.compat)
target_link_libraries(main std.compat)
target_sources(main
PRIVATE
main.cpp
Expand All @@ -218,13 +197,9 @@ Building this project is done with the following steps, assuming the files

$ mkdir build
$ cmake -G Ninja -S . -B build -DCMAKE_CXX_COMPILER=<path-to-compiler> -DLIBCXX_BUILD=<build>
$ ninja -j1 std -C build
$ ninja -C build
$ build/main

.. note:: The ``std`` dependencies of ``std.compat`` is not always resolved when
building the ``std`` target using multiple jobs.

.. warning:: ``<path-to-compiler>`` should point point to the real binary and
not to a symlink.

Expand Down
16 changes: 12 additions & 4 deletions libcxx/modules/CMakeLists.txt.in
Original file line number Diff line number Diff line change
Expand Up @@ -50,10 +50,15 @@ endif()
target_compile_options(std
PUBLIC
-nostdinc++
@LIBCXX_COMPILE_FLAGS@
)
target_compile_options(std
PRIVATE
-Wno-reserved-module-identifier
-Wno-reserved-user-defined-literal
@LIBCXX_COMPILE_FLAGS@
)
target_link_options(std PUBLIC -nostdlib++ -Wl,-rpath,@LIBCXX_LIBRARY_DIR@ -L@LIBCXX_LIBRARY_DIR@)
target_link_libraries(std c++)
set_target_properties(std
PROPERTIES
OUTPUT_NAME "c++std"
Expand All @@ -67,7 +72,7 @@ target_sources(std.compat
std.compat.cppm
)

target_include_directories(std.compat SYSTEM PRIVATE @LIBCXX_CONFIGURED_INCLUDE_DIRS@)
target_include_directories(std.compat SYSTEM PUBLIC @LIBCXX_CONFIGURED_INCLUDE_DIRS@)

if (NOT @LIBCXX_ENABLE_EXCEPTIONS@)
target_compile_options(std.compat PUBLIC -fno-exceptions)
Expand All @@ -76,13 +81,16 @@ endif()
target_compile_options(std.compat
PUBLIC
-nostdinc++
@LIBCXX_COMPILE_FLAGS@
)
target_compile_options(std.compat
PRIVATE
-Wno-reserved-module-identifier
-Wno-reserved-user-defined-literal
-fmodule-file=std=${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/std.dir/std.pcm
@LIBCXX_COMPILE_FLAGS@
)
set_target_properties(std.compat
PROPERTIES
OUTPUT_NAME "c++std.compat"
)
add_dependencies(std.compat std)
target_link_libraries(std.compat PUBLIC std c++)