Allow tomlplusplus to be built by C++20 modules (#266)

CMakeLists.txt

@@ -30,11 +30,26 @@ target_include_directories(
 
 target_compile_features(tomlplusplus_tomlplusplus INTERFACE cxx_std_17)
 
-# ---- Install rules, examples, and fuzzing ----
+# ---- Install rules ----
 if (tomlplusplus_INSTALL)
   include(cmake/install-rules.cmake)
 endif()
 
+# ---- C++ Modules Support (optional) ----
+option(TOMLPLUSPLUS_BUILD_MODULES "Build C++ modules support" OFF)
+
+if(TOMLPLUSPLUS_BUILD_MODULES)
+  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.28)
+    message(STATUS "Building C++ modules (CMake ${CMAKE_VERSION} supports modules)")
+    add_subdirectory(src/modules)
+  else()
+    message(WARNING "Skipping C++ modules (requires CMake 3.28+, found ${CMAKE_VERSION})")
+  endif()
+else()
+  message(STATUS "C++ modules support is disabled. Enable with -DTOMLPLUSPLUS_BUILD_MODULES=ON")
+endif()
+
+# ---- Examples and fuzzing ----
 if(PROJECT_IS_TOP_LEVEL)
   option(BUILD_EXAMPLES "Build examples tree." OFF)
   option(BUILD_FUZZER "Build fuzzer." OFF)

README.md

@@ -20,6 +20,7 @@
 ## Library features
 
 -   Header-only (optional!)
+-   Module support
 -   Supports the latest [TOML] release ([v1.0.0]), plus optional support for some unreleased TOML features
 -   Passes all tests in the [toml-test](https://github.com/toml-lang/toml-test) suite
 -   Supports serializing to JSON and YAML
@@ -110,8 +111,8 @@ You'll find some more code examples in the `examples` directory, and plenty more
 ### 🍨️ Regular flavour
 
 1. Clone the repository
-2. Add `tomlplusplus/include` to your include paths
-3. `#include <toml++/toml.hpp>`
+2. Add `tomlplusplus/include` to your include paths, or for optional module support add `tomlplusplus/modules` as well and enable `TOMLPLUSPLUS_BUILD_MODULES`
+3. `#include <toml++/toml.hpp>` (or `import tomlplusplus;`)
 
 ### Conan
 
@@ -281,13 +282,16 @@ UTF-8 decoding is performed using a state machine based on Bjoern Hoehrmann's '[
 
 ### With thanks to:
 
+-   **[@a-is](https://github.com/a-is)** - Fixed a bug
 -   **[@beastle9end](https://github.com/beastle9end)** - Made Windows.h include bypass
 -   **[@bjadamson](https://github.com/bjadamson)** - Reported some bugs and helped design a new feature
 -   **[@bobfang1992](https://github.com/bobfang1992)** - Reported a bug and created a [wrapper in python](https://github.com/bobfang1992/pytomlpp)
+-   **[@capuanob](https://github.com/capuanob)** - Integrated this project into OSSFuzz
 -   **[@GiulioRomualdi](https://github.com/GiulioRomualdi)** - Added cmake+meson support
 -   **[@jonestristand](https://github.com/jonestristand)** - Designed and implemented the `toml::path`s feature
 -   **[@kcsaul](https://github.com/kcsaul)** - Fixed a bug
 -   **[@levicki](https://github.com/levicki)** - Helped design some new features
+-   **[@mikomikotaishi](https://github.com/mikomikotaishi)** - Added support for C++20 modules
 -   **[@moorereason](https://github.com/moorereason)** - Reported a whole bunch of bugs
 -   **[@mosra](https://github.com/mosra)** - Created the awesome [m.css] used to generate the API docs
 -   **[@N-Dekker](https://github.com/N-Dekker)** - Added a workaround for the legacy lambda processor of MSVC 2019/2022, added `get_line`
@@ -304,11 +308,9 @@ UTF-8 decoding is performed using a state machine based on Bjoern Hoehrmann's '[
 -   **[@std-any-emplace](https://github.com/std-any-emplace)** - Reported some bugs
 -   **[@Tachi107](https://github.com/Tachi107)** - Made some tweaks to meson.build, added compile_library build option
 -   **[@traversaro](https://github.com/traversaro)** - Added vcpkg support and reported a bunch of bugs
+-   **[@tyler92](https://github.com/tyler92)** - Fixed stack overflow that occurred during fuzzing tests
 -   **[@whiterabbit963](https://github.com/whiterabbit963)** - Fixed a bug with value_or conversions
 -   **[@ximion](https://github.com/ximion)** - Added support for installation with meson
--   **[@a-is](https://github.com/a-is)** - Fixed a bug
--   **[@capuanob](https://github.com/capuanob)** - Integrated this project into OSSFuzz
--   **[@tyler92](https://github.com/tyler92)** - Fixed stack overflow that occurred during fuzzing tests
 <br>
 
 ## Contact

docs/pages/main_page.md

@@ -7,6 +7,7 @@
 @section mainpage-features Features
 
 -   Header-only (optional!)
+-   Module support
 -   Supports the latest [TOML](https://toml.io/) release ([v1.0.0](https://toml.io/en/v1.0.0)), plus
     optional support for some unreleased TOML features
 -   Passes all tests in the [toml-test](https://github.com/BurntSushi/toml-test) suite
@@ -37,6 +38,8 @@ Call toml::parse_file() and work with the toml::table you get back, or handle an
 @cpp
 #include <iostream>
 #include <toml++/toml.hpp>
+// or alternatively:
+import tomlplusplus; // if C++20 or later
 
 int main(int argc, char\*\* argv)
 {
@@ -460,8 +463,8 @@ and [emoji sundae] Regular. The API is the same for both.
 
 <h3>[emoji sundae] Regular flavour</h3>
 1. Clone \github{marzer/tomlplusplus, the repository} from GitHub
-2. Add `tomlplusplus/include` to your include paths
-3. `#include <toml++/toml.hpp>`
+2. Add `tomlplusplus/include` to your include paths, or for optional module support add `tomlplusplus/modules` as well and enable `TOMLPLUSPLUS_BUILD_MODULES`
+3. `#include <toml++/toml.hpp>` (or `import tomlplusplus;`)
 
 <!-- --------------------------------------------------------------------------------------------------------------- -->
 

src/modules/CMakeLists.txt

@@ -0,0 +1,39 @@
+file(GLOB_RECURSE TOMLPLUSPLUS_MODULES *.cppm)
+
+add_library(tomlplusplus_modules)
+
+cmake_minimum_required(VERSION 3.28)
+
+if(NOT COMMAND configure_cpp_module_target)
+  function(configure_cpp_module_target target)
+    if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.28)
+      target_sources(${target} PUBLIC FILE_SET CXX_MODULES FILES ${TOMLPLUSPLUS_MODULES})
+    else()
+      message(WARNING "C++ modules require CMake 3.28+. Using standard compilation.")
+      target_sources(${target} PRIVATE ${TOMLPLUSPLUS_MODULES})
+    endif()
+  endfunction()
+endif()
+
+configure_cpp_module_target(tomlplusplus_modules)
+
+target_link_libraries(tomlplusplus_modules
+  PUBLIC
+    tomlplusplus::tomlplusplus
+)
+
+target_include_directories(tomlplusplus_modules
+  PRIVATE
+    ${tomlplusplus_SOURCE_DIR}/include
+)
+
+target_compile_features(tomlplusplus_modules PUBLIC cxx_std_20)
+
+if(TOMLPLUSPLUS_ENABLE_INSTALL)
+  install(TARGETS tomlplusplus_modules
+    EXPORT tomlplusplus-targets
+    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    FILE_SET CXX_MODULES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/tomlplusplus/modules
+  )
+endif()

src/modules/tomlpp.cppm

@@ -0,0 +1,67 @@
+/**
+ * @file tomlpp.cppm
+ * @brief File containing the module declaration for toml++.
+ */
+
+module;
+
+#include <toml++/toml.hpp>
+
+export module tomlplusplus;
+
+/**
+ * @namespace toml
+ * @brief The toml++ namespace toml:: 
+ */
+export namespace toml {
+    /**
+     * @namespace literals
+     * @brief The toml++ namespace toml::literals::
+     */
+    inline namespace literals {
+        using toml::literals::operator""_toml;
+        using toml::literals::operator""_tpath;
+    }
+
+    using toml::array;
+    using toml::date;
+    using toml::date_time;
+    using toml::inserter;
+    using toml::json_formatter;
+    using toml::key;
+    using toml::node;
+    using toml::node_view;
+    using toml::parse_error;
+    using toml::parse_result;
+    using toml::path;
+    using toml::path_component;
+    using toml::source_position;
+    using toml::source_region;
+    using toml::table;
+    using toml::time;
+    using toml::time_offset;
+    using toml::toml_formatter;
+    using toml::value;
+    using toml::yaml_formatter;
+    using toml::format_flags;
+    using toml::node_type;
+    using toml::path_component_type;
+    using toml::value_flags;
+    using toml::array_iterator;
+    using toml::const_array_iterator;
+    using toml::const_table_iterator;
+    using toml::default_formatter;
+    using toml::inserted_type_of;
+    using toml::optional;
+    using toml::source_index;
+    using toml::source_path_ptr;
+    using toml::table_iterator;
+
+    using toml::at_path;
+    using toml::get_line;
+    using toml::operator""_toml;
+    using toml::operator""_tpath;
+    using toml::operator<<;
+    using toml::parse;
+    using toml::parse_file;
+}