Add Separate CMake Target for C++20 Modules (#4685)

* Add Separate CMake Target for C++20 Modules

In the same vein as there is the `fmt::fmt-header-only`, `fmt::fmt` and
`fmt::fmt_c` targets, I propose the addition of a new target
`fmt::fmt-module` which will be for the compilation of the FMT_MODULE
library option.

The new target will have the properties requried for Compiling,
Installing and using the C++20 functionality in CMake

The `add_module_library` function is marked as deprecated as its
functionality is superseded.

Updated the logic for setting the FMT_USE_CMAKE_MODULE flag to check the
versions for Ninja and MSVC according the CMAKE Documents and setting
the FMT_MODULE flag based on this

* Add Separate CMake Target for C++20 Modules

In the same vein as there is the `fmt::fmt-header-only`, `fmt::fmt` and
`fmt::fmt_c` targets, I propose the addition of a new target
`fmt::fmt-module` which will be for the compilation of the FMT_MODULE
library option.

The new target will have the properties requried for Compiling,
Installing and using the C++20 functionality in CMake

Updated the logic for setting the FMT_USE_CMAKE_MODULE flag to check the
versions for Ninja and MSVC according the CMAKE Documents and setting
the FMT_MODULE flag based on this

Fixed the test/CMakeLists.txt file which used the FMT_MODULE flag to
separate the module and non-module library testing, in particular
disableing the module version.

The module testing still needs to be fixed, but the expected behavior of
testing the non-modular version is working.

---------

Co-authored-by: Mathew Benson <mathew@benson.co.ke>
Co-authored-by: ClausKlein <claus.klein@arcormail.de>
This commit is contained in:
Mathew Benson 2026-03-02 20:11:31 +03:00 committed by GitHub
parent fca0445565
commit 4e1b170b44
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
4 changed files with 126 additions and 54 deletions

View File

@ -30,7 +30,7 @@ endfunction()
# DEPRECATED! Should be merged into add_module_library.
function(enable_module target)
if (MSVC)
if(NOT CMAKE_GENERATOR STREQUAL "Ninja")
if (NOT CMAKE_GENERATOR STREQUAL "Ninja")
set(BMI_DIR "${CMAKE_CURRENT_BINARY_DIR}")
file(TO_NATIVE_PATH "${BMI_DIR}/${target}.ifc" BMI)
target_compile_options(${target}
@ -38,31 +38,26 @@ function(enable_module target)
INTERFACE /reference fmt=${BMI})
set_target_properties(${target} PROPERTIES ADDITIONAL_CLEAN_FILES ${BMI})
set_source_files_properties(${BMI} PROPERTIES GENERATED ON)
endif()
endif ()
endif ()
endfunction()
set(FMT_USE_CMAKE_MODULES FALSE)
if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.28 AND
CMAKE_GENERATOR STREQUAL "Ninja")
set(FMT_USE_CMAKE_MODULES TRUE)
endif ()
# Adds a library compiled with C++20 module support.
# `enabled` is a CMake variables that specifies if modules are enabled.
# If modules are disabled `add_module_library` falls back to creating a
# non-modular library.
#
# Usage:
# add_module_library(<name> [sources...] FALLBACK [sources...] [IF enabled])
# add_module_library(<name> [sources...] FALLBACK [sources...] [IF_MODULE enabled]
# [USE_CMAKE_MODULES true])
function(add_module_library name)
cmake_parse_arguments(AML "" "IF" "FALLBACK" ${ARGN})
cmake_parse_arguments(AML "" "IF_MODULE;USE_CMAKE_MODULES" "FALLBACK" ${ARGN})
set(sources ${AML_UNPARSED_ARGUMENTS})
add_library(${name})
set_target_properties(${name} PROPERTIES LINKER_LANGUAGE CXX)
if (NOT ${${AML_IF}})
if (NOT ${AML_IF_MODULE})
# Create a non-modular library.
target_sources(${name} PRIVATE ${AML_FALLBACK})
set_target_properties(${name} PROPERTIES CXX_SCAN_FOR_MODULES OFF)
@ -71,14 +66,14 @@ function(add_module_library name)
# Modules require C++20.
target_compile_features(${name} PUBLIC cxx_std_20)
if (CMAKE_COMPILER_IS_GNUCXX)
target_compile_options(${name} PUBLIC -fmodules-ts)
endif ()
if (FMT_USE_CMAKE_MODULES)
target_sources(${name} PUBLIC FILE_SET fmt TYPE CXX_MODULES
if (${AML_USE_CMAKE_MODULES})
target_sources(${name} PUBLIC FILE_SET fmt_module TYPE CXX_MODULES
FILES ${sources})
else()
else ()
if (CMAKE_COMPILER_IS_GNUCXX)
target_compile_options(${name} PUBLIC -fmodules-ts)
endif ()
# `std` is affected by CMake options and may be higher than C++20.
get_target_property(std ${name} CXX_STANDARD)
@ -121,7 +116,7 @@ function(add_module_library name)
endforeach ()
endif ()
target_sources(${name} PRIVATE ${sources})
endif()
endif ()
endfunction()
include(CMakeParseArguments)
@ -153,6 +148,30 @@ if (FMT_MASTER_PROJECT AND NOT CMAKE_BUILD_TYPE)
endif ()
project(FMT CXX)
# Determine Support for the C++ Module Scanning Features
# Requires C++20, CMake>=3.28 and (Ninja >= 1.11 OR Visual Studio >=17.4)
# The project() CMake Function sets several variables including those
# needed for Compiler Versions
set(FMT_USE_CMAKE_MODULES FALSE)
if (CMAKE_VERSION VERSION_GREATER_EQUAL 3.28
AND CMAKE_CXX_STANDARD GREATER_EQUAL 20)
# Check Version of Ninja to determine CXX_MODULES support
if (CMAKE_GENERATOR STREQUAL "Ninja")
execute_process(COMMAND "${CMAKE_MAKE_PROGRAM}" "--version"
OUTPUT_VARIABLE NINJA_VERSION)
message(STATUS "Ninja Version: ${NINJA_VERSION}")
if (NINJA_VERSION VERSION_GREATER_EQUAL 1.11)
set(FMT_USE_CMAKE_MODULES TRUE)
message(STATUS "Using CXX Modules by Default with Ninja")
endif ()
elseif (CMAKE_GENERATOR MATCHES "^Visual Studio"
AND MSVC_VERSION GREATER_EQUAL 1934)
set(FMT_USE_CMAKE_MODULES TRUE)
message(STATUS "Using CXX Modules by Default with Visual Studio")
endif ()
endif ()
include(GNUInstallDirs)
set_verbose(FMT_INC_DIR ${CMAKE_INSTALL_INCLUDEDIR} CACHE STRING
"Installation directory for include files, a relative path that "
@ -169,14 +188,10 @@ option(FMT_TEST "Generate the test target." ${FMT_MASTER_PROJECT})
option(FMT_FUZZ "Generate the fuzz target." OFF)
option(FMT_CUDA_TEST "Generate the cuda-test target." OFF)
option(FMT_OS "Include OS-specific APIs." ON)
option(FMT_MODULE "Build a module instead of a traditional library." OFF)
option(FMT_MODULE "Build a module library in addition to the traditional library." ${FMT_USE_CMAKE_MODULES})
option(FMT_SYSTEM_HEADERS "Expose headers with marking them as system." OFF)
option(FMT_UNICODE "Enable Unicode support." ON)
if (FMT_TEST AND FMT_MODULE)
# The tests require {fmt} to be compiled as traditional library
message(STATUS "Testing is incompatible with build mode 'module'.")
endif ()
set(FMT_SYSTEM_HEADERS_ATTRIBUTE "")
if (FMT_SYSTEM_HEADERS)
set(FMT_SYSTEM_HEADERS_ATTRIBUTE SYSTEM)
@ -304,15 +319,15 @@ add_headers(FMT_HEADERS args.h base.h chrono.h color.h compile.h core.h format.h
xchar.h)
set(FMT_SOURCES src/format.cc)
add_module_library(fmt src/fmt.cc FALLBACK
${FMT_SOURCES} ${FMT_HEADERS} README.md ChangeLog.md
IF FMT_MODULE)
# add regular library by setting IF_MODULE=FALSE
add_module_library(fmt src/fmt.cc
FALLBACK ${FMT_SOURCES} ${FMT_HEADERS} README.md ChangeLog.md
IF_MODULE FALSE)
add_library(fmt::fmt ALIAS fmt)
if (FMT_MODULE)
enable_module(fmt)
elseif (FMT_OS)
if (FMT_OS)
target_sources(fmt PRIVATE src/os.cc)
else()
else ()
target_compile_definitions(fmt PRIVATE FMT_OS=0)
endif ()
@ -362,6 +377,39 @@ if (FMT_SAFE_DURATION_CAST)
target_compile_definitions(fmt PUBLIC FMT_SAFE_DURATION_CAST)
endif ()
if (FMT_MODULE)
add_module_library(fmt-module "src/fmt.cc"
IF_MODULE TRUE
USE_CMAKE_MODULES ${FMT_USE_CMAKE_MODULES})
add_library(fmt::fmt-module ALIAS fmt-module)
enable_module(fmt-module)
if (FMT_WERROR)
target_compile_options(fmt-module PRIVATE ${WERROR_FLAG})
endif ()
if (FMT_PEDANTIC)
target_compile_options(fmt-module PRIVATE ${PEDANTIC_COMPILE_FLAGS})
endif ()
if (FMT_USE_CMAKE_MODULES)
target_sources(fmt-module PRIVATE FILE_SET fmt_module_headers TYPE HEADERS
BASE_DIRS ${PROJECT_SOURCE_DIR}/include FILES ${FMT_HEADERS})
else ()
target_include_directories(fmt-module ${FMT_SYSTEM_HEADERS_ATTRIBUTE} BEFORE PUBLIC
$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:${FMT_INC_DIR}>)
endif ()
set(FMT_DEBUG_POSTFIX d CACHE STRING "Debug library postfix.")
set_target_properties(fmt-module PROPERTIES
VERSION ${FMT_VERSION}
SOVERSION ${CPACK_PACKAGE_VERSION_MAJOR}
DEBUG_POSTFIX "${FMT_DEBUG_POSTFIX}"
)
endif ()
add_library(fmt-header-only INTERFACE)
add_library(fmt::fmt-header-only ALIAS fmt-header-only)
@ -371,6 +419,9 @@ elseif (FMT_UNICODE)
# Unicode support requires compiling with /utf-8.
target_compile_options(fmt PUBLIC $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:MSVC>>:/utf-8>)
target_compile_options(fmt-header-only INTERFACE $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:MSVC>>:/utf-8>)
if (FMT_MODULE)
target_compile_options(fmt-module PUBLIC $<$<AND:$<COMPILE_LANGUAGE:CXX>,$<CXX_COMPILER_ID:MSVC>>:/utf-8>)
endif ()
else ()
target_compile_definitions(fmt PUBLIC FMT_UNICODE=0)
endif ()
@ -432,10 +483,18 @@ if (FMT_INSTALL)
set(INSTALL_TARGETS fmt fmt-header-only fmt-c)
if (FMT_MODULE)
list(APPEND INSTALL_TARGETS fmt-module)
endif ()
set(INSTALL_FILE_SET)
if (FMT_USE_CMAKE_MODULES)
set(INSTALL_FILE_SET FILE_SET fmt DESTINATION "${FMT_INC_DIR}/fmt")
endif()
if (${CMAKE_VERSION} VERSION_GREATER "3.22")
list(APPEND INSTALL_FILE_SET FILE_SET fmt DESTINATION "${FMT_INC_DIR}/fmt")
list(APPEND INSTALL_FILE_SET FILE_SET fmt_header_only DESTINATION "${FMT_INC_DIR}/fmt")
endif ()
if (FMT_MODULE AND FMT_USE_CMAKE_MODULES)
list(APPEND INSTALL_FILE_SET FILE_SET fmt_module DESTINATION "${FMT_INC_DIR}/fmt")
endif ()
# Install the library and headers.
install(TARGETS ${INSTALL_TARGETS}

View File

@ -20,6 +20,12 @@ The {fmt} library API consists of the following components:
All functions and types provided by the library reside in namespace `fmt`
and macros have prefix `FMT_`.
## C++ Modules API
With the new C++ Modules API, all the headers listed above do not need to
be explicitly #included. We can instead use the `import fmt;` statement instead.
All other functionality, listed below remains the same.
## Base API
`fmt/base.h` defines the base API which provides main formatting functions

View File

@ -8,9 +8,10 @@ with CMake, while the [Build Systems](#build-systems) section covers the rest.
## CMake
{fmt} provides two CMake targets: `fmt::fmt` for the compiled library and
`fmt::fmt-header-only` for the header-only library. It is recommended to use
the compiled library for improved build times.
{fmt} provides three CMake targets: `fmt::fmt` for the standard compiled library,
`fmt::fmt-module` for the C++ modules library and `fmt::fmt-header-only` for the
header-only library. It is recommended to use the compiled library or the module
library for improved build times.
There are three primary ways to use {fmt} with CMake:
@ -40,6 +41,12 @@ There are three primary ways to use {fmt} with CMake:
add_subdirectory(fmt)
target_link_libraries(<your-target> fmt::fmt)
### Alternative Targets
In order to use the header-only target or the module target, simply substitute the
`fmt::fmt` in the above steps with `fmt::fmt-header-only` or `fmt::fmt-module`
accordingly.
## Installation
### Debian/Ubuntu

View File

@ -41,10 +41,6 @@ function(add_fmt_test name)
add_test(NAME ${name} COMMAND ${name})
endfunction()
if (FMT_MODULE)
return ()
endif ()
add_fmt_test(args-test)
add_fmt_test(base-test)
add_fmt_test(assert-test)
@ -86,23 +82,27 @@ add_executable(perf-sanity perf-sanity.cc)
target_link_libraries(perf-sanity fmt::fmt)
if (FMT_MODULE)
# The module-test.cc needs some work and is not working yet.
# For now We simply just return
# so that the other tests are not affected.
return()
# The tests need {fmt} to be compiled as traditional library
# because of visibility of implementation details.
# If module support is present the module tests require a
# test-only module to be built from {fmt}
add_library(test-module OBJECT ${CMAKE_SOURCE_DIR}/src/fmt.cc)
target_compile_features(test-module PUBLIC cxx_std_11)
target_include_directories(test-module PUBLIC
$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>)
enable_module(test-module)
#add_library(test-module OBJECT ${CMAKE_SOURCE_DIR}/src/fmt.cc)
#target_compile_features(test-module PUBLIC cxx_std_11)
#target_include_directories(test-module PUBLIC
# $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>)
#enable_module(test-module)
add_fmt_test(module-test MODULE test-main.cc)
if (MSVC)
target_compile_options(test-module PRIVATE /utf-8 /Zc:__cplusplus
/Zc:externConstexpr /Zc:inline)
target_compile_options(module-test PRIVATE /utf-8 /Zc:__cplusplus
/Zc:externConstexpr /Zc:inline)
endif ()
#add_fmt_test(module-test MODULE test-main.cc)
#if (MSVC)
# target_compile_options(test-module PRIVATE /utf-8 /Zc:__cplusplus
# /Zc:externConstexpr /Zc:inline)
# target_compile_options(module-test PRIVATE /utf-8 /Zc:__cplusplus
# /Zc:externConstexpr /Zc:inline)
#endif ()
endif ()
if (NOT DEFINED MSVC_STATIC_RUNTIME AND MSVC)
@ -112,9 +112,9 @@ if (NOT DEFINED MSVC_STATIC_RUNTIME AND MSVC)
if (${flag_var} MATCHES "^(/|-)(MT|MTd)")
set(MSVC_STATIC_RUNTIME ON)
break()
endif()
endif ()
endforeach()
endif()
endif ()
if (NOT MSVC_STATIC_RUNTIME)
add_executable(posix-mock-test