feat: Add C++ modules support

CMakeLists.txt

@@ -74,6 +74,7 @@ option(JSONCPP_WITH_PKGCONFIG_SUPPORT "Generate and install .pc files" ON)
 option(JSONCPP_WITH_CMAKE_PACKAGE "Generate and install cmake package files" ON)
 option(JSONCPP_WITH_EXAMPLE "Compile JsonCpp example" OFF)
 option(JSONCPP_WITH_INSTALL "Include JsonCpp header and binaries in the install target" ON)
+option(JSONCPP_WITH_MODULE "Compile JsonCpp module" OFF)
 option(JSONCPP_STATIC_WINDOWS_RUNTIME "Use static (MT/MTd) Windows runtime" OFF)
 option(BUILD_SHARED_LIBS "Build jsoncpp_lib as a shared library." ON)
 option(BUILD_STATIC_LIBS "Build jsoncpp_lib as a static library." ON)

jsoncpp-namespaced-targets.cmake

@@ -7,3 +7,7 @@ if (NOT TARGET JsonCpp::JsonCpp)
         set_target_properties(JsonCpp::JsonCpp PROPERTIES INTERFACE_LINK_LIBRARIES "jsoncpp_lib")
     endif ()
 endif ()
+
+if (TARGET jsoncpp_module AND NOT TARGET jsoncpp::module)
+    add_library(jsoncpp::module ALIAS jsoncpp_module)
+endif ()

src/CMakeLists.txt

@@ -3,3 +3,8 @@ if(JSONCPP_WITH_TESTS)
     add_subdirectory(jsontestrunner)
     add_subdirectory(test_lib_json)
 endif()
+
+#install the example
+if(JSONCPP_WITH_MODULE)
+    add_subdirectory(modules)
+endif()

src/modules/CMakeLists.txt

@@ -0,0 +1,41 @@
+cmake_minimum_required(VERSION 3.28)
+
+add_library(jsoncpp_module)
+
+target_sources(jsoncpp_module
+    PUBLIC
+        FILE_SET CXX_MODULES FILES
+            jsoncpp.cppm
+)
+
+target_compile_features(jsoncpp_module PUBLIC cxx_std_20)
+
+if(BUILD_SHARED_LIBS)
+    target_link_libraries(jsoncpp_module PUBLIC jsoncpp_lib)
+elseif(BUILD_STATIC_LIBS)
+    target_link_libraries(jsoncpp_module PUBLIC jsoncpp_static)
+endif()
+
+target_include_directories(jsoncpp_module PUBLIC
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:include>
+)
+
+add_library(jsoncpp::module ALIAS jsoncpp_module)
+
+# Installation
+if(JSONCPP_WITH_CMAKE_PACKAGE)
+    set(MODULE_INSTALL_EXPORT EXPORT jsoncpp)
+else()
+    set(MODULE_INSTALL_EXPORT)
+endif()
+
+if(JSONCPP_WITH_INSTALL)
+    install(TARGETS jsoncpp_module
+        ${MODULE_INSTALL_EXPORT}
+        LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+        RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
+        FILE_SET CXX_MODULES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/jsoncpp/modules
+    )
+endif()

src/modules/jsoncpp.cppm

@@ -0,0 +1,95 @@
+// Copyright 2007-2010 Baptiste Lepilleur and The JsonCpp Authors
+// Distributed under MIT license, or public domain if desired and
+// recognized in your jurisdiction.
+// See file LICENSE for detail or copy at http://jsoncpp.sourceforge.net/LICENSE
+
+module;
+
+#include <json/json.h>
+
+export module jsoncpp;
+
+export namespace Json {
+    // writer.h
+    using Json::StreamWriter;
+    using Json::StreamWriterBuilder;
+    using Json::Writer;
+    using Json::FastWriter;
+    using Json::StyledWriter;
+    using Json::StyledStreamWriter;
+    using Json::valueToString;
+    using Json::valueToQuotedString;
+    using Json::operator<<;
+
+    // reader.h
+    using Json::Reader;
+    using Json::CharReader;
+    using Json::CharReaderBuilder;
+    using Json::parseFromStream;
+    using Json::operator>>;
+
+    // json_features.h
+    using Json::Features;
+
+    // value.h
+    using Json::ArrayIndex;
+    using Json::StaticString;
+    using Json::Path;
+    using Json::PathArgument;
+    using Json::Value;
+    using Json::ValueIteratorBase;
+    using Json::ValueIterator;
+    using Json::ValueConstIterator;
+    using Json::ValueMembersView;
+    using Json::ValueConstMembersView;
+
+    // config.h
+    using Json::version;
+    using Json::Int;
+    using Json::UInt;
+    #ifdef JSON_HAS_INT64
+    using Json::Int64;
+    using Json::UInt64;
+    #endif
+    using Json::LargestInt;
+    using Json::LargestUInt;
+    using Json::Allocator;
+    using Json::String;
+    using Json::IStringStream;
+    using Json::OStringStream;
+    using Json::IStream;
+    using Json::OStream;
+
+    // allocator.h
+    using Json::SecureAllocator;
+    using Json::operator==;
+    using Json::operator!=;
+
+    // value.h
+    #if JSON_USE_EXCEPTION
+    using Json::Exception;
+    using Json::RuntimeError;
+    using Json::LogicError;
+    #endif
+    using Json::ValueType;
+    using Json::CommentPlacement;
+    using Json::PrecisionType;
+    using Json::MemberProxy;
+    using Json::ConstMemberProxy;
+    using Json::nullValue;
+    using Json::intValue;
+    using Json::uintValue;
+    using Json::realValue;
+    using Json::stringValue;
+    using Json::booleanValue;
+    using Json::arrayValue;
+    using Json::objectValue;
+    using Json::commentBefore;
+    using Json::commentAfterOnSameLine;
+    using Json::commentAfter;
+    using Json::numberOfCommentPlacement;
+    using Json::significantDigits;
+    using Json::decimalPlaces;
+    using Json::swap;
+    using Json::writeString;
+} // namespace Json