C++ modules, xmake and compile_commands.json?

[Tomcat-42]

Xmake Version

v2.8.3

Operating System Version and Architecture

arch linux

Describe Bug

I am experimenting with C++ modules and Xmake. Building and running modularized code on xmake works flawlessly, however, clangd seems not to work with the exported compile_commands.json.

I have the latest llvm ecossystem instaled (clang 18.0.0 and the latest libc++) with the experimental clangd modules support applyed on top.

Expected Behavior

Is this a expected behavior? Does Xmake support generating a compile_commands.json compatible with c++ modules?

Project Configuration

My source code tree(basically the stl_headerunit example):

.
├── compile_commands.json
├── src
│  ├── hello.cpp
│  └── main.cpp
├── test.lua
└── xmake.lua

My xmake.lua:

add_rules("mode.release", "mode.debug")
set_languages("c++2b")
set_toolchains("clang")
add_cxxflags(
	"-fmodules",
	"-fimplicit-modules",
	"-fmodule-map-file=/usr/include/c++/v1/module.modulemap",
	"-std=c++2b",
	"-stdlib=libc++",
	"-nostdlib++",
	"-Wall",
	"-Wextra",
	"-Werror",
	"-Wpedantic",
	{ force = true }
)
add_ldflags("-lc++", "-lc++abi", "-lfmt", { force = true })

target("stl_headerunit")
set_kind("binary")
set_policy("build.c++.modules", true)
set_policy("build.c++.clang.stdmodules", true)
add_files("src/*.cpp")

Additional Information and Error Logs

The generation of my compile_commands.json

➜  xmake project -k compile_commands
[  0%]: generating.module.deps src/main.cpp
[  0%]: generating.module.deps src/hello.cpp
create ok!

The file

[
  {
    "directory": "/home/pablo/xmake/tests/projects/c++/modules/stl_headerunit",
    "arguments": [
      "/usr/bin/clang",
      "-Qunused-arguments",
      "-m64",
      "-fvisibility=hidden",
      "-fvisibility-inlines-hidden",
      "-O3",
      "-fmodules",
      "-fimplicit-modules",
      "-fmodule-map-file=/usr/include/c++/v1/module.modulemap",
      "-std=c++2b",
      "-stdlib=libc++",
      "-nostdlib++",
      "-Wall",
      "-Wextra",
      "-Werror",
      "-Wpedantic",
      "-DNDEBUG",
      "-fmodules-cache-path=build/.gens/stl_headerunit/linux/x86_64/release/rules/modules/cache",
      "-x",
      "c++-module",
      "--precompile",
      "-c",
      "src/hello.cpp",
      "-o",
      "build/.gens/stl_headerunit/linux/x86_64/release/rules/modules/cache/37b9dad1/hello.pcm"
    ],
    "file": "src/hello.cpp"
  },
  {
    "directory": "/home/pablo/xmake/tests/projects/c++/modules/stl_headerunit",
    "arguments": [
      "/usr/bin/clang",
      "-c",
      "-Qunused-arguments",
      "-m64",
      "-fvisibility=hidden",
      "-fvisibility-inlines-hidden",
      "-O3",
      "-fmodules",
      "-fimplicit-modules",
      "-fmodule-map-file=/usr/include/c++/v1/module.modulemap",
      "-std=c++2b",
      "-stdlib=libc++",
      "-nostdlib++",
      "-Wall",
      "-Wextra",
      "-Werror",
      "-Wpedantic",
      "-DNDEBUG",
      "-fmodule-file=hello=build/.gens/stl_headerunit/linux/x86_64/release/rules/modules/cache/37b9dad1/hello.pcm",
      "-o",
      "build/.objs/stl_headerunit/linux/x86_64/release/src/main.cpp.o",
      "src/main.cpp"
    ],
    "file": "src/main.cpp"
  },
  {
    "directory": "/home/pablo/xmake/tests/projects/c++/modules/stl_headerunit",
    "arguments": [
      "/usr/bin/clang",
      "-c",
      "-Qunused-arguments",
      "-m64",
      "-fvisibility=hidden",
      "-fvisibility-inlines-hidden",
      "-O3",
      "-fmodules",
      "-fimplicit-modules",
      "-fmodule-map-file=/usr/include/c++/v1/module.modulemap",
      "-std=c++2b",
      "-stdlib=libc++",
      "-nostdlib++",
      "-Wall",
      "-Wextra",
      "-Werror",
      "-Wpedantic",
      "-DNDEBUG",
      "-o",
      "build/.objs/stl_headerunit/linux/x86_64/release/src/hello.cpp.o",
      "src/hello.cpp"
    ],
    "file": "src/hello.cpp"
  }
]

[waruqi]

It should work for 2.8.3

see #4199

[mathstuf]

Note that I don't think compile_commands.json is suitable for module information. There is some effort in SG15 to define a file, similar to compile_commands.json, that does provide sufficient information.

[Tomcat-42]

Idk if the problem is in my setup or in clangd then, because I keep getting the error:

[waruqi]

You can check the generated compile_commands, if the generated flags don't have any problem, it should be an issue with clangd.

[Arthapz]

I'm working on a big refactor of module compilation so maybe somes of your issues Will be fixed
With the current implementation the compile_commands """work""" if your clangd is exactly the same version of the clang used for module compilation but it require full project compilation before linting and (and you need to rebuild your files before the lint get updatef)

[Tomcat-42]

I'm working on a big refactor of module compilation so maybe somes of your issues Will be fixed
With the current implementation the compile_commands """work""" if your clangd is exactly the same version of the clang used for module compilation but it require full project compilation before linting and (and you need to rebuild your files before the lint get updatef)

Yeah, my clangd and clang are both in version 18.0. Also, my stl header modules are generated using my system clang( I compiled libc++ from source), but despite of that I can't get it working.

Let me know when you progress with that. I can help too if you want.

[Arthapz]

I'm working on a big refactor of module compilation so maybe somes of your issues Will be fixed
With the current implementation the compile_commands """work""" if your clangd is exactly the same version of the clang used for module compilation but it require full project compilation before linting and (and you need to rebuild your files before the lint get updatef)

Yeah, my clangd and clang are both in version 18.0. Also, my stl header modules are generated using my system clang( I compiled libc++ from source), but despite of that I can't get it working.

Let me know when you progress with that. I can help too if you want.

No problem, i'll probably recompile my llvm with the clangd PR to try it

[waruqi]

Note that I don't think compile_commands.json is suitable for module information. There is some effort in SG15 to define a file, similar to compile_commands.json, that does provide sufficient information.

Does clangd support it now?

[Tomcat-42]

No, the support is incomplete: llvm/llvm-project#66462.

I think we can close this.

[Tomcat-42]

Note that, despite some intellisense working, I still got errors while importing std modules, like:

Could not build module std_iostream

[Arthapz]

Note that, despite some intellisense working, I still got errors while importing std modules, like:

Could not build module std_iostream

The only way i got the intellisense working is by using only modules (and not headerunits)
On Linux / macOS, and it work only after a full build of the project (and modification of a module interface is only updated after rebuild)