As the xmake C++ module main contributor, i can affirm that xmake module support is ahead of cmake, i added support for gcc, clang and msvc, headerunits, import std, automatic reuse of bmi when flags are compatible,import module from an external package (like glm or vulkan_hpp) and i’m closely watching compilers repository to support new things before compiler release

for clangd i can't do much currently, there is a PR that add some support, i tried it, but doesn't require for now buildsystem intervention

For example:

  add_requires("vulkan-headers", {configs = {modules = true}})

  # xmake.lua
  target("test-vk")
    set_languages("c++latest")
    add_files("src/\*.cpp")
    set_policy("build.c++.modules", true)
    add_packages("vulkan-headers")

  // main.cpp
  import std;
  import vulkan_hpp;

  int main() {
    auto vk_context = vk::raii::Context();

    const auto exts =  vk_context.enumerateInstanceExtensionProperties();
    for(auto &&ext : exts)
        std::println("{}", std::string{ext.extensionName});

    return 0;
  }  

  // result
  > xmake f --toolchain=llvm --runtimes="c++_shared" --yes; xmake b
  checking for platform ... windows
  checking for architecture ... x64
  [  0%]: <test-vk> generating.module.deps src\main.cpp
  [  0%]: <test-vk> generating.module.deps F:\llvm\bin\..\lib\..\share\libc++\v1\std.cppm
  [  0%]: <test-vk> generating.module.deps F:\packages\xmake\v\vulkan-headers\1.3.275+0\ae359cf8d45b4d049acf1ae7350e6dc3\modules\b028617b\vulkan.cppm
  [ 12%]: <test-vk> compiling.module.release std
  [ 12%]: <test-vk> compiling.module.release vulkan_hpp
  [ 62%]: compiling.release src\main.cpp
  [ 75%]: linking.release test-vk.exe
  [100%]: build ok, spent 5.64s

  > xmake run
  VK_KHR_device_group_creation
  VK_KHR_external_fence_capabilities
  VK_KHR_external_memory_capabilities
  VK_KHR_external_semaphore_capabilities
  VK_KHR_get_physical_device_properties2
  VK_KHR_get_surface_capabilities2
  VK_KHR_surface
  VK_KHR_win32_surface
  VK_EXT_debug_report
  VK_EXT_debug_utils
  VK_EXT_swapchain_colorspace
  VK_KHR_portability_enumeration
  VK_LUNARG_direct_driver_loading