cpp20_modules_scan_dependency_demo

This repo show how to scan C++20 Modules dependencies with different compiler.

I prepare foo.cppm which provide a named module foo and an entry demo.cc which consume the module foo.

• foo.cppm

module;
#include <iostream>
export module foo;

export void hello() {
    std::cout << "Hello from C++20 Modules foo" << std::endl;
}

• demo.cc

import foo;

int main() {
    hello();
    return 0;
}

you can see the result from the CI (GitHub Action)

Clang

use clang-scan-deps -format=p1689 -- clang xxx

clang-scan-deps-17 -format=p1689 -- clang++-17 -c -std=c++20 -MD -MF demo.cc.d demo.cc -o demo.o
clang-scan-deps-17 -format=p1689 -- clang++-17 -c -std=c++20 -MD -MF foo.cppm.d foo.cppm -o foo.o

the result of scanning demo.cc

{
    "revision": 0,
    "rules": [
        {
            "primary-output": "demo.o",
            "requires": [
                {
                    "logical-name": "foo"
                }
            ]
        }
    ],
    "version": 1
}

the result of scanning foo.cppm

{
    "revision": 0,
    "rules": [
        {
            "primary-output": "foo.o",
            "provides": [
                {
                    "is-interface": true,
                    "logical-name": "foo",
                    "source-path": "foo.cppm"
                }
            ]
        }
    ],
    "version": 1
}

see also .github/workflows/clang.yml

MSVC

use cl /std:c++latest /scanDependencies- xxx

cl /std:c++latest /scanDependencies- demo.cc /Fodemo.obj
cl /std:c++latest /scanDependencies- /TP foo.cppm /ifcOutput foo.pcm /Fofoo.obj

the result of scanning demo.cc

{
    "version": 1,
    "revision": 0,
    "rules": [
        {
            "primary-output": "demo.obj",
            "outputs": [
                "-"
            ],
            "requires": [
                {
                    "logical-name": "foo"
                }
            ]
        }
    ]
}

the result of scanning foo.cppm

{
    "version": 1,
    "revision": 0,
    "rules": [
        {
            "primary-output": "foo.obj",
            "outputs": [
                "-",
                "foo.pcm"
            ],
            "provides": [
                {
                    "logical-name": "foo",
                    "source-path": "d:\\a\\cpp20_modules_scan_dependency_demo\\cpp20_modules_scan_dependency_demo\\foo.cppm",
                    "is-interface": true
                }
            ],
            "requires": []
        }
    ]
}

see also .github/workflows/msvc.yml

GCC

only test with GCC 14

use gcc-14 -E -MD -MF <path/to/dotd_file> -fdeps-file=<path/to/ddi_file> -fdeps-format=p1689r5 xxx

note -MD -MF <path/to/dotd_file> is required.

the result of scanning demo.cc

gcc-14 -E -x c++ -fmodules-ts -MD -MF demo.d -fdeps-file=/dev/stdout -fdeps-format=p1689r5 demo.cc -o demo.cc.i

the output

{
"rules": [
{
"primary-output": "demo.cc.o",
"requires": [
{
"logical-name": "foo"
}
]
}
],
"version": 0,
"revision": 0
}

the result of scanning foo.cppm

gcc-14 -E -x c++ -fmodules-ts -MD -MF foo.d -fdeps-file=/dev/stdout -fdeps-format=p1689r5 foo.cppm -o foo.cppm.i

the output

{
"rules": [
{
"primary-output": "foo.cppm.o",
"provides": [
{
"logical-name": "foo",
"is-interface": true
}
],
"requires": [
]
}
],
"version": 0,
"revision": 0
}

see also .github/workflows/gcc.yml

References

• Clang Standard C++ Modules
• MSVC Using C++ Modules in MSVC from the Command Line Part 1: Primary Module Interfaces
• GCC C++ Modules
• import CMake; C++20 Modules