feat boost.conversion: initial boost.conversion C++20 modules support

.github/workflows/ci.yml

@@ -18,18 +18,52 @@ jobs:
       matrix:
         include:
           - toolset: gcc-14  # Do not remove! It is the only toolset that tests CMake tests down below
+            compiler: g++-14
             cxxstd: "03,11,14,17,20"
             os: ubuntu-24.04
           - toolset: gcc-12
+            compiler: g++-12
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-22.04
             cxxflags: "cxxflags=--coverage -fsanitize=address,leak,undefined -fno-sanitize-recover=undefined"
             linkflags: "linkflags=--coverage -lasan -lubsan"
             gcov_tool: "gcov-12"
-          - toolset: clang
+          - toolset: clang-14
             compiler: clang++-14
             cxxstd: "03,11,14,17,2a"
             os: ubuntu-22.04
+          - toolset: clang-19
+            compiler: clang++-19
+            cxxstd: "20"
+            cmake_cxx_standard: ""
+            os: ubuntu-24.04
+            install: &cxx19
+              - clang-19
+              - llvm-19
+              - libclang-rt-19-dev
+              - libc++-19-dev
+              - libc++abi-19-dev
+              - clang-tools-19
+          - toolset: clang-19
+            compiler: clang++-19
+            cxxstd: "20"
+            cmake_cxx_standard: 20
+            os: ubuntu-24.04
+            install: *cxx19
+          - toolset: clang-19
+            compiler: clang++-19
+            cxxstd: "23"
+            cmake_cxx_standard: 23
+            os: ubuntu-24.04
+            install: *cxx19
+          - toolset: clang-19
+            compiler: clang++-19
+            cxxstd: "26"
+            cmake_cxx_standard: 26
+            os: ubuntu-24.04
+            install: *cxx19
+
+    name: ${{matrix.os}}, ${{matrix.toolset}}, ${{matrix.cxxstd}}
 
     runs-on: ${{matrix.os}}
 
@@ -38,7 +72,7 @@ jobs:
 
       - name: Install packages
         if: matrix.install
-        run: sudo apt install ${{matrix.install}}
+        run: sudo apt install -y ${{join(matrix.install, ' ')}}
 
       - name: Setup Boost
         run: |
@@ -65,16 +99,50 @@ jobs:
           ./b2 -j4 variant=debug tools/inspect
 
       - name: Run CMake tests
-        if: ${{matrix.toolset == 'gcc-14'}}
+        if: ${{matrix.toolset == 'gcc-14' || matrix.toolset == 'clang-19'}}
         run: |
           cd ../boost-root/
-          mkdir __build
-          cd __build
-          cmake -DBUILD_TESTING=1 -DBOOST_INCLUDE_LIBRARIES=conversion -DCMAKE_CXX_COMPILER=g++-14 -DCMAKE_C_COMPILER=gcc-14 ..
-          cmake --build . --target tests
-          ctest --output-on-failure --no-tests=error
-          cd ..
+          cmake -S . -B __build \
+                -DBUILD_TESTING=1 \
+                -DBOOST_INCLUDE_LIBRARIES=conversion \
+                -DCMAKE_CXX_COMPILER=${{matrix.compiler}} \
+                ${{ matrix.cmake_cxx_standard != '' && format('-DCMAKE_CXX_STANDARD={0}', matrix.cmake_cxx_standard) || '' }}
+          cmake --build __build --target tests
+          ctest --test-dir __build --output-on-failure --no-tests=error
           rm -rf __build
+
+      - name: Run modules tests
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/$LIBRARY
+          cmake -S test/cmake_subdir_test \
+                -B build_module \
+                -GNinja \
+                -DBOOST_USE_MODULES=1 \
+                -DBUILD_TESTING=1 \
+                ${{ matrix.cmake_cxx_standard != '' && format('-DCMAKE_CXX_STANDARD={0}', matrix.cmake_cxx_standard) || '' }} \
+                -DCMAKE_CXX_COMPILER=${{matrix.compiler}} \
+                -DCMAKE_CXX_MODULE_STD=ON \
+                -DCMAKE_EXPERIMENTAL_CXX_IMPORT_STD=0e5b6991-d74f-4b3d-a41c-cf096e0b2508 \
+                -DCMAKE_CXX_FLAGS=-stdlib=libc++
+          cmake --build build_module
+          ctest --test-dir build_module -VV
+          rm -rf build_module
+
+      - name: Run modules tests without 'import std;'
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/$LIBRARY
+          cmake -S test/cmake_subdir_test \
+                -B build_module \
+                -GNinja \
+                -DBOOST_USE_MODULES=1 \
+                -DBUILD_TESTING=1 \
+                ${{ matrix.cmake_cxx_standard != '' && format('-DCMAKE_CXX_STANDARD={0}', matrix.cmake_cxx_standard) || '' }} \
+                -DCMAKE_CXX_COMPILER=${{matrix.compiler}}
+          cmake --build build_module
+          ctest --test-dir build_module -VV
+          rm -rf build_module
 
       - name: Run tests
         run: |
@@ -95,7 +163,7 @@ jobs:
 
           echo "$LCOV --directory ../boost-root/bin.v2/libs/$LIBRARY/ --base-directory `pwd`/libs/$LIBRARY/test --capture --output-file $GITHUB_WORKSPACE/coveralls/coverage.info"
           $LCOV --directory ../boost-root/bin.v2/libs/$LIBRARY/ --base-directory ../boost-root/ --capture --output-file $GITHUB_WORKSPACE/coveralls/coverage.info
-          $LCOV --remove $GITHUB_WORKSPACE/coveralls/coverage.info "/usr*" "*/$LIBRARY/test/*" ${{matrix.ignore_coverage}} "*/$LIBRARY/tests/*" "*/$LIBRARY/examples/*" "*/$LIBRARY/example/*" -o $GITHUB_WORKSPACE/coveralls/coverage.info
+          $LCOV --remove $GITHUB_WORKSPACE/coveralls/coverage.info "/usr*" "*/$LIBRARY/test/*" "*/$LIBRARY/tests/*" "*/$LIBRARY/examples/*" "*/$LIBRARY/example/*" -o $GITHUB_WORKSPACE/coveralls/coverage.info
 
           cd ../boost-root
           OTHER_LIBS=`grep "submodule .*" .gitmodules | sed 's/\[submodule\ "\(.*\)"\]/"\*\/boost\/\1\.hpp" "\*\/boost\/\1\/\*"/g'| sed "/\"\*\/boost\/$LIBRARY\/\*\"/d" | sed ':a;N;$!ba;s/\n/ /g'`

CMakeLists.txt

@@ -1,20 +1,47 @@
-# Copyright 2019 Mike Dev
+# Copyright (c) 2019 Mike Dev
+# Copyright (c) 2025-2026 Fedor Osetrov
+#
 # Distributed under the Boost Software License, Version 1.0.
 # See accompanying file LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
 
-cmake_minimum_required( VERSION 3.5...4.20 )
-project( boost_conversion VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX )
+cmake_minimum_required(VERSION 3.5...4.20)
+project(boost_conversion VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX)
 
-add_library( boost_conversion INTERFACE )
-add_library( Boost::conversion ALIAS boost_conversion )
+if (BOOST_USE_MODULES)
+  add_library(boost_conversion)
+  target_sources(boost_conversion PUBLIC
+    FILE_SET modules_public
+    TYPE CXX_MODULES
+    BASE_DIRS modules
+    FILES ${CMAKE_CURRENT_LIST_DIR}/modules/boost_conversion.cppm
+  )
 
-target_include_directories( boost_conversion INTERFACE include )
+  target_compile_definitions(boost_conversion PUBLIC BOOST_USE_MODULES)
+  get_property(__standard TARGET boost_conversion PROPERTY CXX_STANDARD)
+  if (__standard IN_LIST CMAKE_CXX_COMPILER_IMPORT_STD AND CMAKE_CXX_MODULE_STD)
+    target_compile_features(boost_conversion PUBLIC cxx_std_23)
+    target_compile_definitions(boost_conversion PRIVATE BOOST_CONVERSION_USE_STD_MODULE)
+    message(STATUS "Using `import std;`")
+  else()
+    target_compile_features(boost_conversion PUBLIC cxx_std_20)
+    message(STATUS "`import std;` is not available")
+  endif()
+  unset(__standard)
+  set(__scope PUBLIC)
+else()
+  add_library(boost_conversion INTERFACE)
+  set(__scope INTERFACE)
+endif()
+
+target_include_directories(boost_conversion ${__scope} include)
+add_library(Boost::conversion ALIAS boost_conversion)
 
-target_link_libraries( boost_conversion
-    INTERFACE
+target_link_libraries(boost_conversion
+    ${__scope}
         Boost::assert
         Boost::config
         Boost::throw_exception
+        Boost::smart_ptr
 )
 
 if(BUILD_TESTING)

include/boost/conversion/detail/config.hpp

@@ -0,0 +1,29 @@
+// Copyright (c) 2025-2026 Antony Polukhin
+// Copyright (c) 2025-2026 Fedor Osetrov
+//
+// 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_CONVERSION_DETAIL_CONFIG_HPP
+#define BOOST_CONVERSION_DETAIL_CONFIG_HPP
+
+#if !defined(BOOST_CONVERSION_INTERFACE_UNIT)
+# include <boost/config.hpp>
+# ifdef BOOST_HAS_PRAGMA_ONCE
+# pragma once
+# endif
+#endif
+
+#ifdef BOOST_CONVERSION_INTERFACE_UNIT
+# define BOOST_CONVERSION_BEGIN_MODULE_EXPORT export {
+# define BOOST_CONVERSION_END_MODULE_EXPORT }
+#else
+# define BOOST_CONVERSION_BEGIN_MODULE_EXPORT
+# define BOOST_CONVERSION_END_MODULE_EXPORT
+#endif
+
+#if defined(BOOST_USE_MODULES) && !defined(BOOST_CONVERSION_INTERFACE_UNIT)
+import boost.conversion;
+#endif
+
+#endif

include/boost/implicit_cast.hpp

@@ -1,12 +1,18 @@
-// Copyright David Abrahams 2003.
+//  boost implicit_cast.hpp header file  ----------------------------------------------//
+//  (C) Copyright David Abrahams, 2003.
+//  (C) Copyright Fedor Osetrov, 2025-2026.
+//
 // 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_IMPLICIT_CAST_DWA200356_HPP
 #define BOOST_IMPLICIT_CAST_DWA200356_HPP
 
-#include <boost/config.hpp>
+#include <boost/conversion/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
@@ -22,6 +28,8 @@ template<class T> struct icast_identity
 
 } // namespace detail
 
+BOOST_CONVERSION_BEGIN_MODULE_EXPORT
+
 // implementation originally suggested by C. Green in
 // http://lists.boost.org/MailArchives/boost/msg00886.php
 
@@ -32,7 +40,10 @@ constexpr T implicit_cast (typename boost::detail::icast_identity<T>::type x) {
     return x;
 }
 
+BOOST_CONVERSION_END_MODULE_EXPORT
+
 } // namespace boost
 
+#endif // !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
 
 #endif // BOOST_IMPLICIT_CAST_DWA200356_HPP

include/boost/polymorphic_cast.hpp

@@ -1,14 +1,15 @@
 //  boost polymorphic_cast.hpp header file  ----------------------------------------------//
-
-//  (C) Copyright Kevlin Henney and Dave Abrahams 1999.
-//  (C) Copyright Boris Rasin 2014.
+//  (C) Copyright Kevlin Henney and Dave Abrahams, 1999.
+//  (C) Copyright Boris Rasin, 2014.
+//  (C) Copyright Fedor Osetrov, 2025-2026.
 //  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)
 
 //  See http://www.boost.org/libs/conversion for Documentation.
 
 //  Revision History
+//  08 Fed 26  introduced C++20 modules support
 //  10 Nov 14  polymorphic_pointer_downcast moved to a separate header,
 //             minor improvements to stisfy latest Boost coding style
 //  08 Nov 14  Add polymorphic_pointer_downcast (Boris Rasin)
@@ -49,25 +50,31 @@
 #ifndef BOOST_POLYMORPHIC_CAST_HPP
 #define BOOST_POLYMORPHIC_CAST_HPP
 
-#include <boost/config.hpp>
+#include <boost/conversion/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
 
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
 #endif
 
+#if !defined(BOOST_CONVERSION_INTERFACE_UNIT)
 # include <boost/assert.hpp>
 # include <boost/throw_exception.hpp>
 
 # include <memory>  // std::addressof
 # include <typeinfo>
 # include <type_traits>
+#endif
 
 #if defined(__cpp_constexpr) && __cpp_constexpr >= 201907L
 #define BOOST_CONVERSION_IMPL_CONSTEXPR_DYN_CAST constexpr
 #else
 #define BOOST_CONVERSION_IMPL_CONSTEXPR_DYN_CAST inline
 #endif
 
+BOOST_CONVERSION_BEGIN_MODULE_EXPORT
+
 namespace boost
 {
 //  See the documentation for descriptions of how to choose between
@@ -125,8 +132,12 @@ namespace boost
         );
     }
 
+BOOST_CONVERSION_END_MODULE_EXPORT
+
 } // namespace boost
 
 #undef BOOST_CONVERSION_IMPL_CONSTEXPR_DYN_CAST
 
+#endif // !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
+
 #endif  // BOOST_POLYMORPHIC_CAST_HPP

include/boost/polymorphic_pointer_cast.hpp

@@ -1,6 +1,7 @@
 //  boost polymorphic_pointer_cast.hpp header file  ----------------------------------------------//
 //  (C) Copyright Boris Rasin, 2014-2021.
 //  (C) Copyright Antony Polukhin, 2014-2026.
+//  (C) Copyright Fedor Osetrov, 2025-2026.
 //  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)
@@ -10,16 +11,21 @@
 #ifndef BOOST_CONVERSION_POLYMORPHIC_POINTER_CAST_HPP
 #define BOOST_CONVERSION_POLYMORPHIC_POINTER_CAST_HPP
 
-#include <boost/config.hpp>
+#include <boost/conversion/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
+
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
 #endif
 
+#if !defined(BOOST_CONVERSION_INTERFACE_UNIT)
 # include <boost/assert.hpp>
 # include <boost/pointer_cast.hpp>
 # include <boost/throw_exception.hpp>
+#endif
 
-
+BOOST_CONVERSION_BEGIN_MODULE_EXPORT
 namespace boost
 {
 //  See the documentation for descriptions of how to choose between
@@ -56,5 +62,8 @@ namespace boost
     }
 
 } // namespace boost
+BOOST_CONVERSION_END_MODULE_EXPORT
+
+#endif // !defined(BOOST_USE_MODULES) || defined(BOOST_CONVERSION_INTERFACE_UNIT)
 
 #endif  // BOOST_CONVERSION_POLYMORPHIC_POINTER_CAST_HPP

modules/boost_conversion.cppm

@@ -0,0 +1,34 @@
+// Copyright (c) 2025-2026 Antony Polukhin
+// Copyright (c) 2025-2026 Fedor Osetrov
+//
+// 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)
+
+module;
+
+#include <boost/config.hpp>
+#include <boost/throw_exception.hpp>
+#include <boost/assert.hpp>
+#include <boost/pointer_cast.hpp>
+
+#ifndef BOOST_CONVERSION_USE_STD_MODULE
+#include <memory>
+#include <typeinfo>
+#include <type_traits>
+#endif
+
+#define BOOST_CONVERSION_INTERFACE_UNIT
+
+export module boost.conversion;
+
+#ifdef BOOST_CONVERSION_USE_STD_MODULE
+import std;
+#endif
+
+#ifdef __clang__
+#   pragma clang diagnostic ignored "-Winclude-angled-in-module-purview"
+#endif
+
+#include <boost/implicit_cast.hpp>
+#include <boost/polymorphic_cast.hpp>
+#include <boost/polymorphic_pointer_cast.hpp>