Rewrite modules following the new recommended Boost practice

.github/workflows/ci.yml

@@ -47,6 +47,10 @@ jobs:
           - toolset: clang-15
             cxxstd: "03,11,14,17,20"
             os: ubuntu-22.04
+          - toolset: clang-19
+            cxxstd: "20,23"
+            os: ubuntu-24.04
+            install: clang-19 llvm-19 libclang-rt-19-dev libc++-19-dev libc++abi-19-dev clang-tools-19
           # - toolset: clang
           #   cxxstd: "03,11,14,17,2a"
           #   os: macos-10.15
@@ -87,6 +91,31 @@ jobs:
           ./b2 -d0 headers
           ./b2 variant=debug tools/inspect/build
 
+      - name: Run modules tests
+        if: false
+        # if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/pfr
+          mkdir build_module
+          cd build_module
+          cmake -DBUILD_TESTING=1 -DBOOST_USE_MODULES=1 -DCMAKE_CXX_COMPILER=clang++-19 -DCMAKE_CXX_FLAGS=-stdlib=libc++ -DCMAKE_EXE_LINKER_FLAGS=-stdlib=libc++ -DCMAKE_CXX_STANDARD=23 -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 -G Ninja ..
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
+
+      - name: Run modules tests wihtout 'import std;'
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/pfr
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -GNinja -DCMAKE_CXX_COMPILER=clang++-19 ..
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
+
       - name: Run tests
         run: |
           cd ../boost-root
@@ -177,6 +206,37 @@ jobs:
           cmd /c bootstrap
           b2 -d0 headers
 
+      - name: Run modules tests
+        if: false
+        # if: ${{matrix.toolset == 'msvc-14.3'}}
+        shell: cmd
+        run: |
+          choco install --no-progress ninja
+          call "C:/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Auxiliary/Build/vcvarsall.bat" x64
+          cd ../boost-root/libs/pfr
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -DCMAKE_CXX_STANDARD=23 -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 -G Ninja ..
+          cmake --build .
+          ctest --no-tests=error -V
+          cd ..
+          rm -rf build_module
+
+      - name: Run modules tests wihtout 'import std;'
+        if: ${{matrix.toolset == 'msvc-14.3'}}
+        shell: cmd
+        run: |
+          choco install --no-progress ninja
+          call "C:/Program Files/Microsoft Visual Studio/2022/Enterprise/VC/Auxiliary/Build/vcvarsall.bat" x64
+          cd ../boost-root/libs/pfr
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -DCMAKE_CXX_STANDARD=20 -G Ninja ..
+          cmake --build .
+          ctest --no-tests=error -V
+          cd ..
+          rm -rf build_module
+
       - name: Run tests
         shell: cmd
         run: |

CMakeLists.txt

@@ -4,20 +4,46 @@
 # Distributed under the Boost Software License, Version 1.0.
 # https://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required(VERSION 3.5...3.16)
+cmake_minimum_required(VERSION 3.5...3.31)
 
 project(boost_pfr VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
-add_library(boost_pfr INTERFACE)
-add_library(Boost::pfr ALIAS boost_pfr)
-
-target_include_directories(boost_pfr INTERFACE include)
+if (BOOST_USE_MODULES)
+    add_library(boost_pfr)
+    target_sources(boost_pfr PUBLIC
+        FILE_SET modules_public TYPE CXX_MODULES FILES
+            ${CMAKE_CURRENT_LIST_DIR}/modules/pfr.cppm
+    )
 
-if (CMAKE_VERSION VERSION_GREATER_EQUAL "3.28.0" AND BUILD_MODULE)
-    add_subdirectory(module)
+    target_compile_features(boost_pfr PUBLIC cxx_std_20)
+    target_compile_definitions(boost_pfr PUBLIC BOOST_USE_MODULES)
+    if (CMAKE_CXX_COMPILER_IMPORT_STD)
+        target_compile_definitions(boost_pfr PRIVATE BOOST_PFR_USE_STD_MODULE)
+        message(STATUS "Using `import std;`")
+    else()
+        message(STATUS "`import std;` is not awailable")
+    endif()
+    target_include_directories(boost_pfr PUBLIC include)
+else()
+    add_library(boost_pfr INTERFACE)
+    target_include_directories(boost_pfr INTERFACE include)
 endif()
 
+add_library(Boost::pfr ALIAS boost_pfr)
+
+enable_testing()
 if (BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
-  add_subdirectory(test)
+    add_subdirectory(test)
+endif()
+
+if (BOOST_USE_MODULES AND BUILD_TESTING)
+    add_executable(boost_pfr_module_usage modules/usage_sample.cpp)
+    target_link_libraries(boost_pfr_module_usage PRIVATE Boost::pfr)
+    add_test(NAME boost_pfr_module_usage COMMAND boost_pfr_module_usage)
+
+    # Make sure that mixing includes and imports is fine for different TU
+    add_executable(boost_pfr_module_usage_mu modules/usage_test_mu1.cpp modules/usage_test_mu2.cpp)
+    target_link_libraries(boost_pfr_module_usage_mu PRIVATE Boost::pfr)
+    add_test(NAME boost_pfr_module_usage_mu COMMAND boost_pfr_module_usage_mu)
 endif()
 

doc/pfr.qbk

@@ -554,22 +554,22 @@ parameters provided to `BOOST_PFR_CORE_NAME_PARSING` macro [*and] the initial ou
 
 [section PFR as a C++20 module]
 
-[caution C++20 PFR module support is on early stage, targets and flags may change in the future]
+[caution C++20 PFR module support is on early stage, targets, flags and behavior may change in the future]
 
-If using CMake of version 3.28.0 or higher define CMake option `-DBUILD_MODULE=1`
-to make the `Boost::pfr_module` and `Boost::pfr_module_migration` libraries
-available. With `Boost::pfr_module` C++20 module Boost.PFR could be used:
+If using modern CMake define CMake option `-DBOOST_USE_MODULES=1` to build a C++20 module and
+make the `Boost::pfr` CMake target provide it. After that an explicit usage of C++20 module `boost.pfr` is allowed:
 
 [import ../module/usage_sample.cpp]
 [pfr_module_example]
 
-The `Boost::pfr_module_migration` CMake target gives an ability to
-mix includes and imports of the PFR library in different translation units.
+The `Boost::pfr` CMake target gives an ability to mix includes and imports of the PFR library in different translation units. Moreover,
+if `BOOST_USE_MODULES` macro is defined then all the `boost/pfr/...` includes implicilty do `import boost.pfr;` to give all the
+benifits of modules without changing the existing code.
 
-If not using CMake, then the module could be build manually from the
-`module/pfr.cppm` file. If mixing of includes in imports is desired, additionally
-define `BOOST_PFR_ATTACH_TO_GLOBAL_MODULE` preprocessor macro to attach all the
-module entities to a global module and avoid ODR issues.
+[note For better compile times make sure that `import std;` is available when building the `boost.pfr` module (in CMake logs there should be
+      a 'Using `import std;`' message). ]
+
+If not using CMake, then the module could be build manually from the `module/pfr.cppm` file.
 
 For manual module build the following commands could be used for clang compiler:
 

include/boost/pfr/config.hpp

@@ -8,8 +8,10 @@
 #define BOOST_PFR_CONFIG_HPP
 #pragma once
 
-#if __cplusplus >= 201402L || (defined(_MSC_VER) && defined(_MSVC_LANG) && _MSC_VER > 1900)
+#if !defined(BOOST_USE_MODULES) && (__cplusplus >= 201402L || (defined(_MSC_VER) && defined(_MSVC_LANG) && _MSC_VER > 1900))
 #include <type_traits> // to get non standard platform macro definitions (__GLIBCXX__ for example)
+#elif defined(BOOST_USE_MODULES)
+#include <version>
 #endif
 
 /// \file boost/pfr/config.hpp
@@ -70,8 +72,10 @@
 #endif
 
 #ifndef BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE
+#   if defined(BOOST_USE_MODULES)
+#       define BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE 1
 // Assume that libstdc++ since GCC-7.3 does not have linear instantiation depth in std::make_integral_sequence
-#   if defined( __GLIBCXX__) && __GLIBCXX__ >= 20180101
+#   elif defined( __GLIBCXX__) && __GLIBCXX__ >= 20180101
 #       define BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE 1
 #   elif defined(_MSC_VER)
 #       define BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE 1
@@ -145,12 +149,16 @@
 
 #undef BOOST_PFR_NOT_SUPPORTED
 
-#ifndef BOOST_PFR_BEGIN_MODULE_EXPORT
+#ifdef BOOST_PFR_INTERFACE_UNIT
+#   define BOOST_PFR_BEGIN_MODULE_EXPORT export {
+#   define BOOST_PFR_END_MODULE_EXPORT }
+#else
 #   define BOOST_PFR_BEGIN_MODULE_EXPORT
+#   define BOOST_PFR_END_MODULE_EXPORT
 #endif
 
-#ifndef BOOST_PFR_END_MODULE_EXPORT
-#   define BOOST_PFR_END_MODULE_EXPORT
+#if defined(BOOST_USE_MODULES) && !defined(BOOST_PFR_INTERFACE_UNIT)
+import boost.pfr;
 #endif
 
 #endif // BOOST_PFR_CONFIG_HPP

include/boost/pfr/core.hpp

@@ -9,6 +9,8 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
 #include <boost/pfr/detail/core.hpp>
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
@@ -17,10 +19,12 @@
 #include <boost/pfr/detail/make_integer_sequence.hpp>
 #include <boost/pfr/detail/tie_from_structure_tuple.hpp>
 
+#include <boost/pfr/tuple_size.hpp>
+
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
 #include <type_traits>
 #include <utility>      // metaprogramming stuff
-
-#include <boost/pfr/tuple_size.hpp>
+#endif
 
 /// \file boost/pfr/core.hpp
 /// Contains all the basic tuple-like interfaces \forcedlink{get}, \forcedlink{tuple_size}, \forcedlink{tuple_element_t}, and others.
@@ -249,4 +253,6 @@ BOOST_PFR_END_MODULE_EXPORT
 
 }} // namespace boost::pfr
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
 #endif // BOOST_PFR_CORE_HPP

include/boost/pfr/core_name.hpp

@@ -14,16 +14,20 @@
 
 #include <boost/pfr/detail/config.hpp>
 
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
 #include <boost/pfr/detail/core_name.hpp>
 
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/stdarray.hpp>
 #include <boost/pfr/detail/make_integer_sequence.hpp>
 
-#include <cstddef> // for std::size_t
-
 #include <boost/pfr/tuple_size.hpp>
 
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <cstddef> // for std::size_t
+#endif
+
 /// \file boost/pfr/core_name.hpp
 /// Contains functions \forcedlink{get_name} and \forcedlink{names_as_array} to know which names each field of any \aggregate has.
 ///
@@ -110,4 +114,6 @@ BOOST_PFR_END_MODULE_EXPORT
 
 }} // namespace boost::pfr
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_PFR_INTERFACE_UNIT)
+
 #endif // BOOST_PFR_CORE_NAME_HPP

include/boost/pfr/detail/core14_classic.hpp

@@ -9,13 +9,6 @@
 
 #include <boost/pfr/detail/config.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
-#include <type_traits>
-#include <utility>      // metaprogramming stuff
-#endif
-
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/offset_based_getter.hpp>
 #include <boost/pfr/detail/fields_count.hpp>
@@ -25,6 +18,11 @@ import std;
 #include <boost/pfr/detail/size_t_.hpp>
 #include <boost/pfr/detail/rvalue_t.hpp>
 
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <type_traits>
+#include <utility>      // metaprogramming stuff
+#endif
+
 #ifdef __clang__
 #   pragma clang diagnostic push
 #   pragma clang diagnostic ignored "-Wmissing-braces"

include/boost/pfr/detail/core14_loophole.hpp

@@ -24,13 +24,6 @@
 
 #include <boost/pfr/detail/config.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
-#include <type_traits>
-#include <utility>
-#endif
-
 #include <boost/pfr/detail/offset_based_getter.hpp>
 #include <boost/pfr/detail/fields_count.hpp>
 #include <boost/pfr/detail/make_flat_tuple_of_references.hpp>
@@ -39,6 +32,9 @@ import std;
 #include <boost/pfr/detail/rvalue_t.hpp>
 #include <boost/pfr/detail/unsafe_declval.hpp>
 
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <utility>
+#endif
 
 #ifdef __clang__
 #   pragma clang diagnostic push

include/boost/pfr/detail/core17_generated.hpp

@@ -22,9 +22,7 @@
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/size_t_.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
 #include <type_traits> // for std::conditional_t, std::is_reference
 #endif
 

include/boost/pfr/detail/core_name20_static.hpp

@@ -22,9 +22,7 @@
 #include <boost/pfr/detail/sequence_tuple.hpp>
 #include <boost/pfr/detail/stdarray.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
 #include <type_traits>
 #include <string_view>
 #include <array>

include/boost/pfr/detail/detectors.hpp

@@ -9,9 +9,7 @@
 
 #include <boost/pfr/detail/config.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
 #include <functional>
 #include <type_traits>
 #endif

include/boost/pfr/detail/fields_count.hpp

@@ -12,11 +12,8 @@
 #include <boost/pfr/detail/size_t_.hpp>
 #include <boost/pfr/detail/unsafe_declval.hpp>
 
-#ifdef BOOST_PFR_HAS_STD_MODULE
-import std;
-#else
-#include <climits>      // CHAR_BIT
-#include <cstdint>      // SIZE_MAX
+#if !defined(BOOST_PFR_INTERFACE_UNIT)
+#include <limits>
 #include <type_traits>
 #include <utility>      // metaprogramming stuff
 #endif
@@ -218,13 +215,13 @@ constexpr std::size_t fields_count_compiler_limitation_next(std::size_t n) noexc
 #else
     static_cast<void>(n);
 #endif
-    return SIZE_MAX;
+    return (std::numeric_limits<std::size_t>::max)();
 }
 
 ///////////////////// Fields count upper bound based on sizeof(T)
 template <class T>
 constexpr std::size_t fields_count_upper_bound_loose() noexcept {
-    return sizeof(T) * CHAR_BIT;
+    return sizeof(T) * std::numeric_limits<unsigned char>::digits;
 }
 
 ///////////////////// Fields count binary search.