initial

.github/workflows/cmake.yml

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+name: cmake
+
+on:
+  push:
+    paths:
+      - "**.cpp"
+      - "**.ixx"
+      - "**.cmake"
+      - "**/CMakeLists.txt"
+      - ".github/workflows/cmake.yml"
+
+env:
+  CTEST_NO_TESTS_ACTION: error
+  CTEST_PARALLEL_LEVEL: 4
+
+
+jobs:
+
+  windows-msvc:
+    runs-on: windows-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - run: cmake --workflow --preset debug

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.28...3.30)
+
+project(CppModules LANGUAGES CXX)
+
+enable_testing()
+
+include(CheckCXXSymbolExists)
+
+
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 23)
+endif()
+
+include(cmake/compilers.cmake)
+
+add_subdirectory(src)
+
+file(GENERATE OUTPUT .gitignore CONTENT "*")

CMakePresets.json

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+{
+  "version": 6,
+
+"configurePresets": [
+{
+  "name": "default",
+  "binaryDir": "${sourceDir}/build",
+  "cacheVariables": {
+    "CMAKE_COMPILE_WARNING_AS_ERROR": true
+  }
+},
+{
+  "name": "multi", "inherits": "default",
+  "displayName": "Ninja Multi-Config",
+  "generator": "Ninja Multi-Config"
+},
+{
+  "name": "msvc", "inherits": "default",
+  "generator": "Visual Studio 17 2022",
+  "cacheVariables": {
+    "CMAKE_COMPILE_WARNING_AS_ERROR": false
+  }
+}
+],
+"buildPresets": [
+  {
+    "name": "default",
+    "configurePreset": "default"
+  },
+  {
+    "name": "release",
+    "configurePreset": "multi",
+    "configuration": "Release"
+  },
+  {
+    "name": "debug",
+    "configurePreset": "multi",
+    "configuration": "Debug"
+  },
+  {
+    "name": "msvc-debug",
+    "configurePreset": "msvc",
+    "configuration": "Debug"
+  }
+],
+"testPresets": [
+{
+  "name": "default",
+  "configurePreset": "default",
+  "output": {
+    "outputOnFailure": true,
+    "verbosity": "verbose"
+  },
+  "execution": {
+    "noTestsAction": "error",
+    "scheduleRandom": true,
+    "stopOnFailure": false,
+    "timeout": 60
+  }
+},
+{
+  "name": "release", "inherits": "default",
+  "configurePreset": "multi",
+  "configuration": "Release"
+},
+{
+  "name": "debug", "inherits": "default",
+  "configurePreset": "multi",
+  "configuration": "Debug"
+},
+{
+  "name": "msvc-debug", "inherits": "default",
+  "configurePreset": "msvc",
+  "configuration": "Debug"
+}
+],
+"workflowPresets": [
+  {
+    "name": "default",
+    "steps": [
+      {
+        "type": "configure",
+        "name": "default"
+      },
+      {
+        "type": "build",
+        "name": "default"
+      },
+      {
+        "type": "test",
+        "name": "default"
+      }
+    ]
+  },
+  {
+    "name": "debug",
+    "steps": [
+      {
+        "type": "configure",
+        "name": "multi"
+      },
+      {
+        "type": "build",
+        "name": "debug"
+      },
+      {
+        "type": "test",
+        "name": "debug"
+      }
+    ]
+  },
+  {
+    "name": "release",
+    "steps": [
+      {
+        "type": "configure",
+        "name": "multi"
+      },
+      {
+        "type": "build",
+        "name": "release"
+      },
+      {
+        "type": "test",
+        "name": "release"
+      }
+    ]
+  },
+  {
+    "name": "msvc",
+    "steps": [
+      {
+        "type": "configure",
+        "name": "msvc"
+      },
+      {
+        "type": "build",
+        "name": "msvc-debug"
+      },
+      {
+        "type": "test",
+        "name": "msvc-debug"
+      }
+    ]
+  }
+]
+}

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2024 scivision
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Readme.md

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+# C++ modules with CMake
+
+[![cmake](https://github.com/scivision/CppModules/actions/workflows/cmake.yml/badge.svg)](https://github.com/scivision/CppModules/actions/workflows/cmake.yml)
+
+C++ modules require recent C++ compilers such as:
+
+* Visual Studio ≥ [16.8](https://devblogs.microsoft.com/cppblog/standard-c20-modules-support-with-msvc-in-visual-studio-2019-version-16-8/)
+* GCC ≥ 14
+* Clang ≥ 16
+
+The Ninja generator is required for C++ modules with CMake.
+
+## Reference
+
+A fully working
+[ball pit simulation](https://github.com/cdacamar/ball_pit)
+shows more advanced use of C++ modules.
+
+https://www.kitware.com/import-cmake-c20-modules/
+
+https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html

cmake/compilers.cmake

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+if(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
+# /std:c++20 or newer implicitly enables modules
+# https://learn.microsoft.com/en-us/cpp/build/reference/experimental-module
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 14.1)
+  add_compile_options(-fmodules-ts)
+elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 17)
+# -std=c++20 or higher implicitly enables modules
+# https://releases.llvm.org/17.0.1/tools/clang/docs/StandardCPlusPlusModules.html#how-to-enable-standard-c-modules
+endif()
+
+check_cxx_symbol_exists(__cpp_modules "" HAVE_CXX_MODULES)
+# Clang 19 didn't have __cpp_modules
+if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND NOT HAVE_CXX_MODULES)
+  message(FATAL_ERROR "${CMAKE_CXX_COMPILER_ID} ${CMAKE_CXX_COMPILER_VERSION} does not support C++20 modules")
+endif()
+
+check_cxx_symbol_exists(__cpp_lib_modules "version" HAVE_STD_MODULES)

src/CMakeLists.txt

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+if(MSVC AND HAVE_STD_MODULES)
+  find_file(msvc_std_src NAMES std.ixx
+  PATHS $ENV{VCToolsInstallDir}/modules
+  NO_DEFAULT_PATH)
+
+  if(msvc_std_src)
+
+  set(msvc_std_ifc ${CMAKE_CURRENT_BINARY_DIR}/std.ifc)
+
+  add_custom_target(msvc_std
+    COMMAND ${CMAKE_CXX_COMPILER} /std:c++latest /EHsc /nologo /c ${msvc_std_src}
+    VERBATIM
+    BYPRODUCTS ${msvc_std_ifc}
+  )
+
+  cmake_path(CONVERT ${msvc_std_ifc} TO_NATIVE_PATH_LIST msvc_std_ifc)
+
+
+  add_executable(msvc_core msvc_core.cpp)
+  target_compile_options(msvc_core PRIVATE /reference ${msvc_std_ifc})
+  add_dependencies(msvc_core msvc_std)
+
+  add_test(NAME msvc_core COMMAND msvc_core)
+
+  else()
+    message(WARNING "Cannot find MSVC std.ixx, skipping import std example")
+  endif()
+endif()
+
+add_executable(math_mod math.cpp)
+# https://cmake.org/cmake/help/latest/command/target_sources.html#file-sets
+target_sources(math_mod PUBLIC
+FILE_SET my_math
+TYPE CXX_MODULES
+FILES math.ixx
+)
+
+add_test(NAME MathModule COMMAND math_mod)

src/math.cpp

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+#include <iostream>
+#include <cassert>
+
+import math;
+
+int main(){
+   int a=1;
+   int b=2;
+
+   int absum = add(a, b);
+   int abdif = subtract(a, b);
+
+   assert(a + b == absum);
+   assert(a - b == abdif);
+
+   std::cout << "OK: Modules demo" << std::endl;
+
+   return EXIT_SUCCESS;
+}

src/math.ixx

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+export module math;
+
+export int add(int a, int b){
+    return a + b;
+}
+
+export int subtract(int a, int b){
+    return a - b;
+}

src/msvc_core.cpp

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+// https://docs.microsoft.com/en-us/cpp/cpp/modules-cpp?view=msvc-170#consume-the-c-standard-library-as-modules
+
+import std;
+
+int main(){
+
+  std::cout << "hello" << std::endl;
+  return 0;
+
+}