C++Module: Fixing import std on enum header and using export import std when appropriate (KhronosGroup#2283)

* fix std import on enum header

* remove duplicate contents in cppm

* moved dynamic enabling of std module into macro header

* do not automatically enable import std

* automatic opt-out approach for export import std

* added opt-out option VULKAN_HPP_NO_STD_MODULE

* add VULKAN_HPP_NO_STD_MODULE to CI workflows

* added VULKAN_HPP_NO_STD_MODULE flag to the readme

* set VULKAN_HPP_NO_STD_MODULE to OFF by default

* added import_std exclusion to ubuntu-ext CI

Author: M2-TE

.github/workflows/ci-macos.yml

@@ -112,6 +112,7 @@ jobs:
               -D VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=ON        \
               -D VULKAN_HPP_BUILD_WITH_LOCAL_VULKAN_HPP=ON    \
               -D VULKAN_HPP_PRECOMPILE=OFF                    \
+              -D VULKAN_HPP_NO_STD_MODULE=ON                  \
               -D CMAKE_CXX_COMPILER=${{matrix.compiler}}      \
               -D CMAKE_CXX_STANDARD=$CXX_STANDARD             \
               -D CMAKE_BUILD_TYPE=$BUILD_TYPE

.github/workflows/ci-ubuntu-22.yml

@@ -120,6 +120,7 @@ jobs:
               -D VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=ON     \
               -D VULKAN_HPP_BUILD_WITH_LOCAL_VULKAN_HPP=ON \
               -D VULKAN_HPP_PRECOMPILE=OFF                 \
+              -D VULKAN_HPP_NO_STD_MODULE=ON               \
               -D CMAKE_CXX_COMPILER=${{matrix.compiler}}   \
               -D CMAKE_CXX_STANDARD=$CXX_STANDARD          \
               -D CMAKE_BUILD_TYPE=$BUILD_TYPE

.github/workflows/ci-ubuntu-24.yml

@@ -125,6 +125,7 @@ jobs:
               -D VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=ON        \
               -D VULKAN_HPP_BUILD_WITH_LOCAL_VULKAN_HPP=ON    \
               -D VULKAN_HPP_PRECOMPILE=OFF                    \
+              -D VULKAN_HPP_NO_STD_MODULE=ON                  \
               -D CMAKE_CXX_COMPILER=${{matrix.compiler}}      \
               -D CMAKE_CXX_STANDARD=$CXX_STANDARD             \
               -D CMAKE_BUILD_TYPE=$BUILD_TYPE

.github/workflows/ci-ubuntu-ext.yml

@@ -131,6 +131,7 @@ jobs:
               -D VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=ON                \
               -D VULKAN_HPP_BUILD_WITH_LOCAL_VULKAN_HPP=ON            \
               -D VULKAN_HPP_PRECOMPILE=OFF                            \
+              -D VULKAN_HPP_NO_STD_MODULE=ON                          \
               -D CMAKE_CXX_COMPILER=clang++-${{matrix.clang_version}} \
               -D CMAKE_CXX_STANDARD=$CXX_STANDARD                     \
               -D CMAKE_BUILD_TYPE=$BUILD_TYPE

.github/workflows/ci-windows.yml

@@ -112,6 +112,7 @@ jobs:
               -D VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=ON        \
               -D VULKAN_HPP_BUILD_WITH_LOCAL_VULKAN_HPP=ON    \
               -D VULKAN_HPP_PRECOMPILE=OFF                    \
+              -D VULKAN_HPP_NO_STD_MODULE=ON                  \
               -D CMAKE_CXX_STANDARD=$CXX_STANDARD             \
               -D CMAKE_BUILD_TYPE=$BUILD_TYPE
             cmake --build build --parallel --clean-first

CMakeLists.txt

@@ -56,6 +56,7 @@ option( VULKAN_HPP_NO_NODISCARD_WARNINGS "Remove C++17 [[nodiscard]] from functi
 option( VULKAN_HPP_NO_SETTERS "Remove setters for structs and unions" OFF )
 option( VULKAN_HPP_NO_SMART_HANDLE "Remove the vk::UniqueHandle helper class" OFF )
 option( VULKAN_HPP_NO_SPACESHIP_OPERATOR "Remove the C++20 <=> (spaceship) operator" OFF )
+option( VULKAN_HPP_NO_STD_MODULE "Prevent the automatic use of import std in the C++20 module when compiling with C++23" OFF )
 option( VULKAN_HPP_NO_TO_STRING "Remove inclusion of vulkan_to_string.hpp from vulkan.hpp" OFF )
 option( VULKAN_HPP_NO_WIN32_PROTOTYPES "Remove HINSTANCE, LoadLibraryA and other symbols, which are declared if VULKAN_HPP_ENABLE_DYNAMIC_LOADER_TOOL is enabled on Win32" OFF )
 option( VULKAN_HPP_RAII_NO_EXCEPTIONS "Do not throw exceptions when vulkan functions from vk::raii return an error code." OFF )
@@ -278,6 +279,9 @@ endif()
 if( VULKAN_HPP_NO_SPACESHIP_OPERATOR )
 	target_compile_definitions(VulkanHpp INTERFACE "VULKAN_HPP_NO_SPACESHIP_OPERATOR" )
 endif()
+if( VULKAN_HPP_NO_STD_MODULE )
+	target_compile_definitions(VulkanHpp INTERFACE "VULKAN_HPP_NO_STD_MODULE" )
+endif()
 
 function( vulkan_hpp__setup_vulkan_include )
 	set( options )

README.md

@@ -74,6 +74,7 @@ The goal of the Vulkan-Hpp is to provide header only C++ bindings for the Vulkan
 	- [VULKAN_HPP_NO_SETTERS](#no_setters)
 	- [VULKAN_HPP_NO_SMART_HANDLE](#no_smart_handle)
 	- [VULKAN_HPP_NO_SPACESHIP_OPERATOR](#no_spaceship_operator)
+	- [VULKAN_HPP_NO_STD_MODULE](#no_std_module)
 	- [VULKAN_HPP_NO_TO_STRING](#no_to_string)
 	- [VULKAN_HPP_NO_WIN32_PROTOTYPES](#no_win32_prototypes)
 	- [VULKAN_HPP_RAII_NO_EXCEPTIONS](#raii_no_exceptions)
@@ -1053,6 +1054,11 @@ By defining `VULKAN_HPP_NO_SMART_HANDLE` before including `vulkan.hpp`, the help
 
 With C++20, the so-called spaceship-operator `<=>` is introduced. If that operator is supported, all the structs and classes in vulkan.hpp use the default implementation of it. As currently some implementations of this operator are very slow, and others seem to be incomplete, by defining `VULKAN_HPP_NO_SPACESHIP_OPERATOR` before including `vulkan.hpp` you can remove that operator from those structs and classes.
 
+#### VULKAN_HPP_NO_STD_MODULE <a id='no_std_module'>
+
+When compiling the `vulkan.cppm` module with C++23, it will automatically try to use `import std`.
+There might be cases where your toolchain is not set up to deal with `import std` or wrongfully defines `__cpp_lib_modules`, for which you can define `VULKAN_HPP_NO_STD_MODULE` to disable `import std` altogether.
+
 #### VULKAN_HPP_NO_TO_STRING <a id='no_to_string'>
 
 By default, the file [`vulkan_to_string.hpp`](vulkan/vulkan_to_string.hpp) is included by `vulkan.hpp` and provides functions `vk::to_string` for enums and bitmasks. If you don't need those functions, you can define `VULKAN_HPP_NO_TO_STRING` to prevent that inclusion. If you have certain files where you want to use those functions nevertheless, you can explicitly include `vulkan_to_string.hpp` there.

snippets/CppmTemplate.hpp

@@ -5,10 +5,9 @@
 
 module;
 
-#include <vulkan/vulkan_hpp_macros.hpp>
-
-#if defined( __cpp_lib_modules ) && !defined( VULKAN_HPP_ENABLE_STD_MODULE )
-#define VULKAN_HPP_ENABLE_STD_MODULE
+#include <version>
+#if defined( __cpp_lib_modules ) && !defined( VULKAN_HPP_NO_STD_MODULE )
+#  define VULKAN_HPP_ENABLE_STD_MODULE
 #endif
 
 #include <vulkan/${api}.hpp>
@@ -17,11 +16,11 @@ module;
 #include <vulkan/${api}_hash.hpp>
 #include <vulkan/${api}_raii.hpp>
 #include <vulkan/${api}_shared.hpp>
-#ifndef VULKAN_HPP_NO_TO_STRING
-#include <vulkan/${api}_to_string.hpp>
-#endif
 
 export module ${api}_hpp;
+#if defined( VULKAN_HPP_ENABLE_STD_MODULE )
+  export import VULKAN_HPP_STD_MODULE;
+#endif
 
 export namespace VULKAN_HPP_NAMESPACE
 {

snippets/EnumsHppTemplate.hpp

@@ -6,7 +6,11 @@
 // include-what-you-use: make sure, vulkan.hpp is used by code-completers
 // IWYU pragma: private, include "vulkan/vulkan.hpp"
 
-#include <type_traits>    // for std::underlying_type
+#if defined( VULKAN_HPP_ENABLE_STD_MODULE ) && defined( VULKAN_HPP_STD_MODULE )
+import VULKAN_HPP_STD_MODULE;
+#else
+#  include <type_traits>    // for std::underlying_type
+#endif
 
 namespace VULKAN_HPP_NAMESPACE
 {

snippets/MacrosHppTemplate.hpp

@@ -82,7 +82,7 @@
 #  define VULKAN_HPP_SUPPORT_SPAN
 #endif
 
-#if defined( __cpp_lib_modules ) && !defined( VULKAN_HPP_STD_MODULE ) && defined( VULKAN_HPP_ENABLE_STD_MODULE )
+#if !defined( VULKAN_HPP_STD_MODULE ) && defined( VULKAN_HPP_ENABLE_STD_MODULE )
 #  define VULKAN_HPP_STD_MODULE std.compat
 #endif