xmake-cxx-modules

Building C++20 Modules with Xmake

Xmake has first-class C++20 modules support across GCC, Clang, and MSVC. It handles the BMI (Built Module Interface) cache, dependency scanning, and per-compiler flag differences automatically — you mostly just point it at the files and enable the policy.

1. Prerequisites

• C++20 language version.
• A new-ish compiler: GCC 14+, Clang 16+ (better: 17+), MSVC 19.34+ (VS 2022 17.4+).
• build.c++.modules policy enabled.

2. Minimal executable with modules

Project layout:

myapp/
├── xmake.lua
└── src/
    ├── main.cpp             # importer (regular .cpp)
    └── math.mpp             # module interface

// src/math.mpp
export module math;

export int add(int a, int b) {
    return a + b;
}

// src/main.cpp
import math;
#include <iostream>

int main() {
    std::cout << add(2, 3) << "\n";
    return 0;
}

-- xmake.lua
add_rules("mode.debug", "mode.release")

target("myapp")
    set_kind("binary")
    set_languages("c++20")
    set_policy("build.c++.modules", true)
    add_files("src/main.cpp", "src/math.mpp")

Build + run:

xmake f -m release
xmake
xmake run myapp

That's it — xmake scans the .mpp, builds the BMI, and links.

3. File extension conventions

Xmake recognizes all common module interface extensions:

Extension	Used by	Notes
.mpp	xmake convention	Recommended — cross-compiler
.cppm	Clang convention	Works everywhere with xmake
.ixx	MSVC convention	Works everywhere with xmake
.mxx	Alternative	Also recognized
.cpp	Regular source	Only a module if it starts with module; or export module

Use whichever you prefer; xmake treats them uniformly. .mpp is the xmake default in examples.

4. Module target kinds

Binary (executable)

target("app")
    set_kind("binary")
    set_languages("c++20")
    set_policy("build.c++.modules", true)
    add_files("src/*.cpp", "src/*.mpp")