Implement initial version of C++20 module boost.any (#30)

`#include <boost/any...` is now implicitly does `import boost.any` if the modules are supported 
All the library internals now have unconditional module level linkage.

Significant differences from https://anarthal.github.io/cppblog/modules3:
* `BOOST_ANY_USE_STD_MODULE` macro switch for `import std;` / `includes` while building module. This allows to use module in C++20 and even without usable  `std` module.

Author: apolukhin

.github/workflows/ci.yml

@@ -27,6 +27,10 @@ jobs:
             compiler: clang++-14
             cxxstd: "03,11,14,17,2a"
             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
@@ -65,7 +69,32 @@ 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 -d0 headers
-          ./b2 -j4 variant=debug tools/inspect/build
+          ./b2 -j4 variant=debug tools/inspect
+
+      - name: Run modules tests wihtout 'import std;'
+        if: ${{matrix.toolset == 'clang-19'}}
+        run: |
+          cd ../boost-root/libs/any
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=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/any
+          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 tests
         run: |
@@ -114,6 +143,10 @@ jobs:
             cxxstd: "03,11,14,17,2a"
             addrmd: 64
             os: windows-2019
+          - toolset: msvc-14.3
+            cxxstd: "14,17,20,latest"
+            addrmd: 32,64
+            os: windows-2022
 
     runs-on: ${{matrix.os}}
 
@@ -142,6 +175,36 @@ jobs:
           cmd /c bootstrap
           b2 -d0 headers
 
+      - name: Run modules tests
+        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/any
+          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 ../test/cmake_subdir_test/
+          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/any
+          mkdir build_module
+          cd build_module
+          cmake -DBOOST_USE_MODULES=1 -DBUILD_TESTING=1 -DCMAKE_CXX_STANDARD=20 -G Ninja ../test/cmake_subdir_test/
+          cmake --build .
+          ctest --no-tests=error -V
+          cd ..
+          rm -rf build_module
+
       - name: Run tests
         shell: cmd
         run: |

CMakeLists.txt

@@ -2,17 +2,43 @@
 # 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...3.20 )
+cmake_minimum_required( VERSION 3.5...3.31 )
 project( boost_any VERSION "${BOOST_SUPERPROJECT_VERSION}" LANGUAGES CXX )
 
-add_library( boost_any INTERFACE )
-add_library( Boost::any ALIAS boost_any )
+if (BOOST_USE_MODULES)
+    add_library(boost_any)
+    target_sources(boost_any PUBLIC
+        FILE_SET modules_public TYPE CXX_MODULES FILES
+            ${CMAKE_CURRENT_LIST_DIR}/modules/boost_any.cppm
+    )
 
-target_include_directories( boost_any INTERFACE include )
+    target_compile_features(boost_any PUBLIC cxx_std_20)
+    target_compile_definitions(boost_any PUBLIC BOOST_USE_MODULES)
+    if (CMAKE_CXX_COMPILER_IMPORT_STD)
+        target_compile_definitions(boost_any PRIVATE BOOST_ANY_USE_STD_MODULE)
+        message(STATUS "Using `import std;`")
+    else()
+        message(STATUS "`import std;` is not awailable")
+    endif()
+    set(__scope PUBLIC)
+else()
+    add_library(boost_any INTERFACE)
+    set(__scope INTERFACE)
+endif()
 
+target_include_directories(boost_any ${__scope} include)
 target_link_libraries( boost_any
-    INTERFACE
+    ${__scope}
         Boost::config
         Boost::throw_exception
         Boost::type_index
 )
+
+add_library( Boost::any ALIAS boost_any )
+
+enable_testing()
+if(BUILD_TESTING AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/test/CMakeLists.txt")
+
+  add_subdirectory(test)
+
+endif()

doc/any.qbk

@@ -237,6 +237,40 @@ The specific requirements on value types to be used in an
 
 [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::any` CMake target provide it. After that an explicit usage of C++20 module `boost.any` is allowed:
+
+[import ../modules/usage_sample.cpp]
+[any_module_example]
+
+The `Boost::any` 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/any...` includes implicilty do `import boost.any;` to give all the
+benifits of modules without changing the existing code.
+
+[note For better compile times make sure that `import std;` is available when building the `boost.any` 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_any.cppm` file.
+
+For manual module build the following commands could be used for clang compiler:
+
+```
+cd any/modules
+clang++ -I ../include -std=c++20 --precompile -x c++-module boost_any.cppm
+```
+
+After that, the module could be used in the following way:
+
+```
+clang++ -std=c++20 -fmodule-file=boost_any.pcm boost_any.pcm usage_sample.cpp
+```
+
+[endsect]
+
 [xinclude autodoc_any.xml]
 
 [section Acknowledgements]

include/boost/any.hpp

@@ -3,13 +3,26 @@
 #ifndef BOOST_ANY_INCLUDED
 #define BOOST_ANY_INCLUDED
 
+#include <boost/any/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
+/// \file boost/any.hpp
+/// \brief \copybrief boost::any
+
+#ifndef BOOST_ANY_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
-/// \file boost/any.hpp
-/// \brief \copybrief boost::any
+#include <memory>  // for std::addressof
+#include <type_traits>
+
+#include <boost/throw_exception.hpp>
+#include <boost/type_index.hpp>
+
+#endif  // #ifndef BOOST_ANY_INTERFACE_UNIT
 
 // what:  variant type boost::any
 // who:   contributed by Kevlin Henney,
@@ -21,14 +34,11 @@
 #include <boost/any/bad_any_cast.hpp>
 #include <boost/any/fwd.hpp>
 #include <boost/any/detail/placeholder.hpp>
-#include <boost/throw_exception.hpp>
-#include <boost/type_index.hpp>
 
-#include <memory>  // for std::addressof
-#include <type_traits>
+namespace boost {
+
+BOOST_ANY_BEGIN_MODULE_EXPORT
 
-namespace boost
-{
     /// \brief A class whose instances can hold instances of any
     /// type that satisfies \forcedlink{ValueType} requirements.
     class any
@@ -355,6 +365,9 @@ namespace boost
         );
         return boost::any_cast<ValueType>(operand);
     }
+
+BOOST_ANY_END_MODULE_EXPORT
+
 }
 
 // Copyright Kevlin Henney, 2000, 2001, 2002. All rights reserved.
@@ -364,4 +377,6 @@ namespace boost
 // accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt)
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
 #endif

include/boost/any/bad_any_cast.hpp

@@ -9,6 +9,11 @@
 #ifndef BOOST_ANYS_BAD_ANY_CAST_HPP_INCLUDED
 #define BOOST_ANYS_BAD_ANY_CAST_HPP_INCLUDED
 
+#include <boost/any/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
+#ifndef BOOST_ANY_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 #   pragma once
@@ -19,9 +24,12 @@
 #endif
 
 #include <stdexcept>
+#endif  // #ifndef BOOST_ANY_INTERFACE_UNIT
 
 namespace boost {
 
+BOOST_ANY_BEGIN_MODULE_EXPORT
+
 /// The exception thrown in the event of a failed boost::any_cast of
 /// an boost::any, boost::anys::basic_any or boost::anys::unique_any value.
 class BOOST_SYMBOL_VISIBLE bad_any_cast :
@@ -39,7 +47,10 @@ class BOOST_SYMBOL_VISIBLE bad_any_cast :
     }
 };
 
+BOOST_ANY_END_MODULE_EXPORT
+
 } // namespace boost
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
 
 #endif // #ifndef BOOST_ANYS_BAD_ANY_CAST_HPP_INCLUDED

include/boost/any/basic_any.hpp

@@ -10,28 +10,36 @@
 #ifndef BOOST_ANYS_BASIC_ANY_HPP_INCLUDED
 #define BOOST_ANYS_BASIC_ANY_HPP_INCLUDED
 
+#include <boost/any/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
+/// \file boost/any/basic_any.hpp
+/// \brief \copybrief boost::anys::basic_any
+
+#ifndef BOOST_ANY_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
-/// \file boost/any/basic_any.hpp
-/// \brief \copybrief boost::anys::basic_any
+#include <memory>  // for std::addressof
+#include <type_traits>
 
-#include <boost/any/bad_any_cast.hpp>
-#include <boost/any/fwd.hpp>
 #include <boost/assert.hpp>
 #include <boost/type_index.hpp>
 #include <boost/throw_exception.hpp>
+#endif  // #ifndef BOOST_ANY_INTERFACE_UNIT
 
-#include <memory>  // for std::addressof
-#include <type_traits>
-
+#include <boost/any/bad_any_cast.hpp>
+#include <boost/any/fwd.hpp>
 
 namespace boost {
 
 namespace anys {
 
+BOOST_ANY_BEGIN_MODULE_EXPORT
+
     /// \brief A class with customizable Small Object Optimization whose
     /// instances can hold instances of any type that satisfies
     /// \forcedlink{ValueType} requirements. Use boost::any instead if not sure.
@@ -546,11 +554,19 @@ namespace anys {
     }
     /// @endcond
 
+BOOST_ANY_END_MODULE_EXPORT
+
 } // namespace anys
 
+BOOST_ANY_BEGIN_MODULE_EXPORT
+
 using boost::anys::any_cast;
 using boost::anys::unsafe_any_cast;
 
+BOOST_ANY_END_MODULE_EXPORT
+
 } // namespace boost
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
 #endif // #ifndef BOOST_ANYS_BASIC_ANY_HPP_INCLUDED

include/boost/any/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_ANY_ANYS_DETAIL_CONFIG_HPP
+#define BOOST_ANY_ANYS_DETAIL_CONFIG_HPP
+
+#ifdef BOOST_ANY_INTERFACE_UNIT
+#   define BOOST_ANY_BEGIN_MODULE_EXPORT export {
+#   define BOOST_ANY_END_MODULE_EXPORT }
+#else
+#   define BOOST_ANY_BEGIN_MODULE_EXPORT
+#   define BOOST_ANY_END_MODULE_EXPORT
+#endif
+
+#if defined(BOOST_USE_MODULES) && !defined(BOOST_ANY_INTERFACE_UNIT)
+import boost.any;
+#endif
+
+#endif  // #ifndef BOOST_ANY_ANYS_DETAIL_CONFIG_HPP

include/boost/any/detail/placeholder.hpp

@@ -7,12 +7,18 @@
 #ifndef BOOST_ANY_ANYS_DETAIL_PLACEHOLDER_HPP
 #define BOOST_ANY_ANYS_DETAIL_PLACEHOLDER_HPP
 
+#include <boost/any/detail/config.hpp>
+
+#if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
+#ifndef BOOST_ANY_INTERFACE_UNIT
 #include <boost/config.hpp>
 #ifdef BOOST_HAS_PRAGMA_ONCE
 # pragma once
 #endif
 
 #include <boost/type_index.hpp>
+#endif
 
 /// @cond
 namespace boost {
@@ -30,4 +36,6 @@ class BOOST_SYMBOL_VISIBLE placeholder {
 } // namespace boost
 /// @endcond
 
+#endif  // #if !defined(BOOST_USE_MODULES) || defined(BOOST_ANY_INTERFACE_UNIT)
+
 #endif  // #ifndef BOOST_ANY_ANYS_DETAIL_PLACEHOLDER_HPP