Implement initial version of C++20 module boost.lexical_cast

.github/workflows/ci.yml

@@ -37,6 +37,10 @@ jobs:
           - toolset: clang
             cxxstd: "11,14,17,20"
             os: macos-13
+          - 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
 
     runs-on: ${{matrix.os}}
 
@@ -70,6 +74,32 @@ jobs:
           python tools/boostdep/depinst/depinst.py --include benchmark --include example --include examples --include tools --git_args "--depth 10 --jobs 3" $LIBRARY
           ./bootstrap.sh
           ./b2 -j4 variant=debug tools/inspect
+      - name: Run modules tests wihtout 'import std;'
+
+
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/lexical_cast
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -GNinja -DCMAKE_CXX_COMPILER=clang++-19 ../test/cmake_subdir_test/
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
+
+      - name: Run modules tests
+        if: false
+        # if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/lexical_cast
+          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 ../test/cmake_subdir_test/
+          cmake --build .
+          ctest -V
+          cd ..
+          rm -rf build_module
 
       - name: Run CMake tests
         if: ${{matrix.toolset == 'gcc-14'}}
@@ -173,8 +203,35 @@ jobs:
           cmake -DBUILD_TESTING=1 -DBOOST_INCLUDE_LIBRARIES=lexical_cast ..
           cmake --build . --target tests --config Debug
           ctest --output-on-failure --no-tests=error -C Debug
-          cd ..
-          rm -rf __build
+
+      - 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/lexical_cast
+          rm -rf build_module
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DCMAKE_CXX_STANDARD=23 -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest --no-tests=error -V
+
+      - 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/lexical_cast
+          rm -rf build_module
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DCMAKE_CXX_STANDARD=20 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest --no-tests=error -V
 
       - name: Run tests
         shell: cmd

CMakeLists.txt

@@ -3,23 +3,43 @@
 # 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...4.0)
 
 project(boost_lexical_cast VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
-add_library(boost_lexical_cast INTERFACE)
-add_library(Boost::lexical_cast ALIAS boost_lexical_cast)
 
-target_include_directories(boost_lexical_cast INTERFACE include)
+if (BOOST_USE_MODULES)
+    add_library(boost_lexical_cast)
+    target_sources(boost_lexical_cast PUBLIC
+        FILE_SET modules_public TYPE CXX_MODULES FILES
+            ${CMAKE_CURRENT_LIST_DIR}/modules/boost_lexical_cast.cppm
+    )
+
+    target_compile_features(boost_lexical_cast PUBLIC cxx_std_20)
+    target_compile_definitions(boost_lexical_cast PUBLIC BOOST_USE_MODULES)
+    if (CMAKE_CXX_COMPILER_IMPORT_STD)
+        target_compile_definitions(boost_lexical_cast PRIVATE BOOST_LEXICAL_CAST_USE_STD_MODULE)
+        message(STATUS "Using `import std;`")
+    else()
+        message(STATUS "`import std;` is not awailable")
+    endif()
+    set(__scope PUBLIC)
+else()
+    add_library(boost_lexical_cast INTERFACE)
+    set(__scope INTERFACE)
+endif()
 
+target_include_directories(boost_lexical_cast ${__scope} include)
 target_link_libraries(boost_lexical_cast
-  INTERFACE
+  ${__scope}
     Boost::config
     Boost::container
     Boost::core
     Boost::throw_exception
 )
 
+add_library(Boost::lexical_cast ALIAS boost_lexical_cast)
+
 if(BUILD_TESTING)
   add_subdirectory(test)
 endif()

doc/lexical_cast.qbk

@@ -233,8 +233,45 @@ limitation of compiler options that you use.
 
 [endsect]
 
+[section C++20 module]
+
+[caution C++20 module support is on early stage, targets, flags and behavior may change in the future]
+
+If using modern CMake define CMake option `-DBOOST_USE_MODULES=1` to build a C++20 module and
+make the `Boost::lexical_cast` CMake target provide it. After that an explicit usage of C++20 module `boost.lexical_cast` is allowed:
+
+[import ../modules/usage_sample.cpp]
+[lexical_cast_module_example]
+
+The `Boost::lexical_cast` CMake target gives an ability to mix includes and imports of the library in different translation units. Moreover,
+if `BOOST_USE_MODULES` macro is defined then all the `boost/lexical_cast...` includes implicitly do `import boost.lexical_cast;` to give all the
+benefits of modules without changing the existing code.
+
+[note For better compile times make sure that `import std;` is available when building the `boost.lexical_cast` 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 `modules/boost_lexical_cast.cppm` file.
+
+For manual module build the following commands could be used for clang compiler:
+
+```
+cd lexical_cast/modules
+clang++ -I ../include -std=c++20 --precompile -x c++-module boost_lexical_cast.cppm
+```
+
+After that, the module could be used in the following way:
+
+```
+clang++ -std=c++20 -fmodule-file=boost_lexical_cast.pcm boost_lexical_cast.pcm usage_sample.cpp
+```
+
+[endsect]
+
 [section Changes]
 
+* [*boost 1.91.0 :]
+    * Added C++20 modules support.
+
 * [*boost 1.86.0 :]
 
     * Fixed conversion of `std::basic_string_view` and `boost::basic_string_view`

include/boost/lexical_cast.hpp

@@ -18,10 +18,16 @@
 #ifndef BOOST_LEXICAL_CAST_INCLUDED
 #define BOOST_LEXICAL_CAST_INCLUDED
 
+#include <boost/lexical_cast/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
+#ifndef BOOST_LEXICAL_CAST_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
 #endif
+#endif
 
 #if defined(BOOST_NO_STRINGSTREAM) || defined(BOOST_NO_STD_WSTRING)
 #define BOOST_LCAST_NO_WCHAR_T
@@ -34,6 +40,7 @@
 
 namespace boost
 {
+BOOST_LEXICAL_CAST_BEGIN_MODULE_EXPORT
     template <typename Target, typename Source>
     inline Target lexical_cast(const Source &arg)
     {
@@ -94,9 +101,12 @@ namespace boost
         );
     }
 
+BOOST_LEXICAL_CAST_END_MODULE_EXPORT
 } // namespace boost
 
 #undef BOOST_LCAST_NO_WCHAR_T
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
 #endif // BOOST_LEXICAL_CAST_INCLUDED
 

include/boost/lexical_cast/bad_lexical_cast.hpp

@@ -18,6 +18,11 @@
 #ifndef BOOST_LEXICAL_CAST_BAD_LEXICAL_CAST_HPP
 #define BOOST_LEXICAL_CAST_BAD_LEXICAL_CAST_HPP
 
+#include <boost/lexical_cast/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
+#ifndef BOOST_LEXICAL_CAST_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
@@ -26,9 +31,11 @@
 #include <exception>
 #include <typeinfo>
 #include <boost/throw_exception.hpp>
+#endif
 
 namespace boost
 {
+BOOST_LEXICAL_CAST_BEGIN_MODULE_EXPORT
     // exception used to indicate runtime lexical_cast failure
     class BOOST_SYMBOL_VISIBLE bad_lexical_cast :
     // workaround MSVC bug with std::bad_cast when _HAS_EXCEPTIONS == 0
@@ -80,6 +87,7 @@ namespace boost
         const type_info_t *target;
 #endif
     };
+BOOST_LEXICAL_CAST_END_MODULE_EXPORT
 
     namespace conversion { namespace detail {
 #ifdef BOOST_NO_TYPEID
@@ -97,4 +105,6 @@ namespace boost
 
 } // namespace boost
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
 #endif // BOOST_LEXICAL_CAST_BAD_LEXICAL_CAST_HPP

include/boost/lexical_cast/detail/buffer_view.hpp

@@ -7,12 +7,18 @@
 #ifndef BOOST_LEXICAL_CAST_DETAIL_BUFFER_VIEW_HPP
 #define BOOST_LEXICAL_CAST_DETAIL_BUFFER_VIEW_HPP
 
+#include <boost/lexical_cast/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
+#ifndef BOOST_LEXICAL_CAST_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
 #endif
 
 #include <iosfwd>
+#endif
 
 namespace boost { namespace conversion { namespace detail {
 
@@ -55,5 +61,7 @@ namespace boost { namespace conversion { namespace detail {
 
 }}}  // namespace boost::conversion::detail
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
 #endif // BOOST_LEXICAL_CAST_DETAIL_BUFFER_VIEW_HPP
 

include/boost/lexical_cast/detail/config.hpp

@@ -0,0 +1,22 @@
+// Copyright Antony Polukhin, 2021-2025.
+//
+// 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)
+
+#ifndef BOOST_LEXICAL_CAST_DETAIL_CONFIG_HPP
+#define BOOST_LEXICAL_CAST_DETAIL_CONFIG_HPP
+
+#ifdef BOOST_LEXICAL_CAST_INTERFACE_UNIT
+#   define BOOST_LEXICAL_CAST_BEGIN_MODULE_EXPORT export {
+#   define BOOST_LEXICAL_CAST_END_MODULE_EXPORT }
+#else
+#   define BOOST_LEXICAL_CAST_BEGIN_MODULE_EXPORT
+#   define BOOST_LEXICAL_CAST_END_MODULE_EXPORT
+#endif
+
+#if defined(BOOST_USE_MODULES) && !defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+import boost.lexical_cast;
+#endif
+
+#endif  // #ifndef BOOST_LEXICAL_CAST_DETAIL_CONFIG_HPP

include/boost/lexical_cast/detail/converter_lexical.hpp

@@ -18,6 +18,11 @@
 #ifndef BOOST_LEXICAL_CAST_DETAIL_CONVERTER_LEXICAL_HPP
 #define BOOST_LEXICAL_CAST_DETAIL_CONVERTER_LEXICAL_HPP
 
+#include <boost/lexical_cast/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
+#ifndef BOOST_LEXICAL_CAST_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
@@ -27,25 +32,26 @@
 #define BOOST_LCAST_NO_WCHAR_T
 #endif
 
+#include <array>
 #include <cstddef>
 #include <string>
 #include <type_traits>
 #include <boost/limits.hpp>
-#include <boost/detail/lcast_precision.hpp>
-
-#include <boost/lexical_cast/detail/widest_char.hpp>
-#include <boost/lexical_cast/detail/is_character.hpp>
-#include <boost/lexical_cast/detail/type_traits.hpp>
 
 #include <array>
 
 #ifndef BOOST_NO_CXX17_HDR_STRING_VIEW
 #include <string_view>
 #endif
 
-#include <boost/lexical_cast/detail/buffer_view.hpp>
 #include <boost/container/container_fwd.hpp>
 
+#endif  // #ifndef BOOST_LEXICAL_CAST_INTERFACE_UNIT
+
+#include <boost/lexical_cast/detail/lcast_precision.hpp>
+#include <boost/lexical_cast/detail/widest_char.hpp>
+#include <boost/lexical_cast/detail/is_character.hpp>
+#include <boost/lexical_cast/detail/buffer_view.hpp>
 #include <boost/lexical_cast/detail/converter_lexical_streams.hpp>
 
 namespace boost {
@@ -479,5 +485,7 @@ namespace boost {
 
 #undef BOOST_LCAST_NO_WCHAR_T
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_LEXICAL_CAST_INTERFACE_UNIT)
+
 #endif // BOOST_LEXICAL_CAST_DETAIL_CONVERTER_LEXICAL_HPP