g++-16 fails to build magic_enum with import std; on macos

[ClausKlein]

cmake version 4.3.4

CMake suite maintained and supported by Kitware (kitware.com/cmake).
cmake -S . -B build -G Ninja \
	 -D MAGIC_ENUM_USE_MODULES=YES \
	 -D MAGIC_ENUM_OPT_BUILD_TESTS=YES \
	 -D CMAKE_CXX_MODULE_STD=YES \
	 -D CMAKE_CXX_STDLIB_MODULES_JSON=/opt/homebrew/Cellar/gcc/16.1.0/lib/gcc/current/libstdc++.modules.json \
	 -D CMAKE_BUILD_TYPE=Release \
	 -D CMAKE_CXX_STANDARD=23 -D CMAKE_CXX_EXTENSIONS=NO -D CMAKE_CXX_STANDARD_REQUIRED=YES \
	 -D CMAKE_INSTALL_MESSAGE=LAZY \
	 -D CMAKE_SKIP_INSTALL_RULES=NO \
	 --log-level=VERBOSE --fresh \
	 # -D CMAKE_CXX_FLAGS='-fno-inline --coverage' \
	 # --trace-expand --trace-source=use-fetch-content.cmake \
	 # --debug-find-pkg=GTest
-- The CXX compiler identification is GNU 16.1.0
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /opt/homebrew/bin/g++-16 - skipped
-- Detecting CXX compile features
CMake Warning (dev) at /opt/homebrew/share/cmake/Modules/Compiler/CMakeCommonCompilerMacros.cmake:226 (cmake_language):
  CMake's support for `import std;` in C++23 and newer is experimental.  It
  is meant only for experimentation and feedback to CMake developers.
Call Stack (most recent call first):
  /opt/homebrew/share/cmake/Modules/CMakeDetermineCompilerSupport.cmake:110 (cmake_cxx_find_modules_json)
  /opt/homebrew/share/cmake/Modules/CMakeTestCXXCompiler.cmake:83 (CMAKE_DETERMINE_COMPILER_SUPPORT)
  CMakeLists.txt:14 (project)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Detecting CXX compile features - done
magic_enum: using import std
-- Performing Test HAS_CPP20_FLAG
-- Performing Test HAS_CPP20_FLAG - Success
-- Performing Test HAS_CPP23_FLAG
-- Performing Test HAS_CPP23_FLAG - Success
magic_enum_module_test-cpp23: using import std
magic_enum_module_test_aliases-cpp23: using import std
magic_enum_module_test_wchar_t-cpp23: using import std
-- Configuring done (1.9s)
-- Generating done (0.0s)
-- Build files have been written to: /Users/runner/work/magic_enum/magic_enum/build
ln -sf build/compile_commands.json .
ninja -C build
ninja: Entering directory `build'
[1/78] Scanning /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.compat.cc for CXX dependencies
[2/78] Scanning /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.cc for CXX dependencies
[3/78] Generating CXX dyndep file CMakeFiles/__cmake_cxx_std_23.dir/CXX.dd
FAILED: [code=1] CMakeFiles/__cmake_cxx_std_23.dir/CXX.dd CMakeFiles/__cmake_cxx_std_23.dir/CXXModules.json CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.cc.o.modmap CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.compat.cc.o.modmap 
/opt/homebrew/bin/cmake -E cmake_ninja_dyndep --tdi=CMakeFiles/__cmake_cxx_std_23.dir/CXXDependInfo.json --lang=CXX --modmapfmt=gcc --dd=CMakeFiles/__cmake_cxx_std_23.dir/CXX.dd @CMakeFiles/__cmake_cxx_std_23.dir/CXX.dd.rsp
CMake Error: Output CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.cc.o is of type `CXX_MODULES` but does not provide a module interface unit or partition
CMake Error: Output CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.compat.cc.o is of type `CXX_MODULES` but does not provide a module interface unit or partition
[4/78] Scanning /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm for CXX dependencies
[5/78] Scanning /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm for CXX dependencies
[6/78] Scanning /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm for CXX dependencies
[7/78] Scanning /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm for CXX dependencies
ninja: build stopped: subcommand failed.
make: *** [all] Error 1
Error: Process completed with exit code 2.

[ClausKlein]

[48/78] Building CXX object CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.cc.o
[49/78] Building CXX object CMakeFiles/__cmake_cxx_std_23.dir/opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.compat.cc.o
[50/78] Building CXX object CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o
FAILED: [code=1] CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o CMakeFiles/magic_enum.dir/magic_enum.gcm 
/opt/homebrew/bin/g++-16 -DMAGIC_ENUM_USE_STD_MODULE -I/Users/runner/work/magic_enum/magic_enum/include/magic_enum -I/Users/runner/work/magic_enum/magic_enum/include -stdlib=libstdc++ -O3 -DNDEBUG -std=c++23 -arch arm64 -MD -MT CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o -MF CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o.d -fmodules-ts -fmodule-mapper=CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o.modmap -MD -fdeps-format=p1689r5 -x c++ -o CMakeFiles/magic_enum.dir/module/magic_enum.cppm.o -c /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:80,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/_types.h:27,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/stdlib.h:64,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/cstdlib:83,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/stdlib.h:36,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/assert.h:44,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/cassert:46,
                 from /Users/runner/work/magic_enum/magic_enum/include/magic_enum/magic_enum.hpp:68,
                 from /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm:50:
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_pthread/_pthread_types.h:57:8: error: conflicting declaration 'struct __darwin_pthread_handler_rec'
   57 | struct __darwin_pthread_handler_rec {
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:80,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/_types.h:27,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/runetype.h:42,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/_ctype.h:70,
                 from /Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/ctype.h:69,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/cctype:47,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/aarch64-apple-darwin23/bits/stdc++.h:33,
                 from /opt/homebrew/Cellar/gcc/16.1.0/include/c++/16/bits/std.cc:26,
of module std, imported at /Users/runner/work/magic_enum/magic_enum/module/magic_enum.cppm:39:
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_pthread/_pthread_types.h:57:8: note: previous declaration as 'struct __darwin_pthread_handler_rec'
   57 | struct __darwin_pthread_handler_rec {
      |        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

# . . .

see too my extended CI builds on ClausKlein#1

[ClausKlein]

But it is magic! This compiles with g++-16 on my iMac:

#if USE_IMPORT_STD
import std;
import magic_enum;
#else
#  include <bit>
#  include <bitset>
#  include <cstdint>
#  include <iostream>
#  include <magic_enum/magic_enum.hpp>
#endif

enum class Color { RED = -10, BLUE = 0, GREEN = 10 };

int test() {
  Color c1 = Color::RED;
  std::cout << magic_enum::enum_name(c1) << std::endl;  // RED
  return 0;
}

int main() {
  test();

  for (const std::uint8_t i : {0, 0b11111111, 0b11110000, 0b00011110}) {
    std::cout << "countl_zero( " << std::bitset<8>(i) << " ) = " << std::countl_zero(i) << '\n';
  }
}

[11/13] /usr/local/bin/g++-16 -DMAGIC_ENUM_USE_STD_MODULE -isystem /Users/clausklein/.local/include -isystem /Users/clausklein/.local/include/magic_enum -stdlib=libstdc++ -std=c++23 -fmodule-only -MD -MT 'CMakeFiles/magic_enum__magic_enum@synth_0.dir/5ee6459ec2d3.bmi' -MF CMakeFiles/magic_enum__magic_enum@synth_0.dir/5ee6459ec2d3.bmi.d -fmodules-ts -fmodule-mapper=CMakeFiles/magic_enum__magic_enum@synth_0.dir/5ee6459ec2d3.bmi.modmap -MD -fdeps-format=p1689r5 -x c++ -o 'CMakeFiles/magic_enum__magic_enum@synth_0.dir/5ee6459ec2d3.bmi' -c /Users/clausklein/.local/share/magic_enum/magic_enum.cppm
[12/13] ccache /usr/local/bin/g++-16 -DUSE_IMPORT_STD -isystem /Users/clausklein/.local/include -isystem /Users/clausklein/.local/include/magic_enum -stdlib=libstdc++ -std=c++23 -MD -MT CMakeFiles/BitManipulation.dir/bit_manipulation.cpp.o -MF CMakeFiles/BitManipulation.dir/bit_manipulation.cpp.o.d -fmodules-ts -fmodule-mapper=CMakeFiles/BitManipulation.dir/bit_manipulation.cpp.o.modmap -MD -fdeps-format=p1689r5 -x c++ -o CMakeFiles/BitManipulation.dir/bit_manipulation.cpp.o -c /Users/clausklein/Workspace/cpp/cxx20/boost-cmake/examples/bit_manipulation.cpp
[13/13] : && /usr/local/bin/g++-16 -stdlib=libstdc++ -Wl,-search_paths_first -Wl,-headerpad_max_install_names CMakeFiles/BitManipulation.dir/bit_manipulation.cpp.o -o BitManipulation  /Users/clausklein/.local/lib/libmagic_enum.a  lib@cmake_cxx_std.a && 

[Neargye]

Hi @ClausKlein, please check new master, I try to fix some problems.

[ClausKlein]

Hi @ClausKlein, please check new master, I try to fix some problems.

Yes, works better, great!

Only some notes:

• cmake v4..4 is out, needs CMAKE_EXPERIMENTAL_CXX_IMPORT_STD=f35a9ac6-8463-4d38-8eec-5d6008153e7d
• no tests with --std=c++26?
• FILE_SET HEADERS should no need to use:

 target_include_directories(
   ${name} ${_scope} $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>

bash-5.3$ CXX=g++-16 gmake all test install
Warning: gcc 16.1.0 is already installed and up-to-date.
To reinstall 16.1.0, run:
  brew reinstall gcc
Warning: llvm 22.1.8 is already installed and up-to-date.
To reinstall 22.1.8, run:
  brew reinstall llvm
Warning: ninja 1.13.2 is already installed and up-to-date.
To reinstall 1.13.2, run:
  brew reinstall ninja
Warning: fmt 12.2.0 is already installed and up-to-date.
To reinstall 12.2.0, run:
  brew reinstall fmt
cmake --version
cmake version 4.4.0-rc3-g068f9d3

CMake suite maintained and supported by Kitware (kitware.com/cmake).
cmake -S . -B build -G Ninja \
 -D MAGIC_ENUM_USE_MODULES=YES \
 -D MAGIC_ENUM_OPT_BUILD_TESTS=YES \
 -D CMAKE_BUILD_TYPE=Release \
 -D CMAKE_EXPERIMENTAL_CXX_IMPORT_STD=f35a9ac6-8463-4d38-8eec-5d6008153e7d \
 -D CMAKE_CXX_MODULE_STD=YES \
 -D CMAKE_CXX_STDLIB_MODULES_JSON=/usr/local/Cellar/gcc/16.1.0/lib/gcc/current/libstdc++.modules.json \
 -D CMAKE_CXX_STANDARD=26 -D CMAKE_CXX_EXTENSIONS=NO -D CMAKE_CXX_STANDARD_REQUIRED=YES \
 -D CMAKE_INSTALL_MESSAGE=LAZY \
 -D CMAKE_SKIP_INSTALL_RULES=NO \
 --log-level=VERBOSE --fresh \
 # -D CMAKE_CXX_FLAGS='-fno-inline --coverage' \
 # --trace-expand --trace-source=use-fetch-content.cmake \
 # --debug-find-pkg=GTest
-- The CXX compiler identification is GNU 16.1.0
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - no
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - no
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/local/bin/g++-16 - skipped
-- Detecting CXX compile features
CMake Warning (experimental) at /Users/clausklein/.local/share/cmake-4.4/Modules/Compiler/CMakeCommonCompilerMacros.cmake:226 (cmake_language):
  CMake's support for `import std;` in C++23 and newer is experimental.  It
  is meant only for experimentation and feedback to CMake developers.
Call Stack (most recent call first):
  /Users/clausklein/.local/share/cmake-4.4/Modules/CMakeDetermineCompilerSupport.cmake:157 (cmake_cxx_find_modules_json)
  /Users/clausklein/.local/share/cmake-4.4/Modules/CMakeTestCXXCompiler.cmake:81 (CMAKE_DETERMINE_COMPILER_SUPPORT)
  CMakeLists.txt:13 (project)
This warning is for project developers.  Use -Wno-author or -Wno-experimental
to suppress it.

-- Detecting CXX compile features - done
magic_enum: using import std
-- Performing Test HAS_CPP20_FLAG
-- Performing Test HAS_CPP20_FLAG - Success
-- Performing Test HAS_CPP23_FLAG
-- Performing Test HAS_CPP23_FLAG - Success
magic_enum_module_test-cpp26: using import std
magic_enum_module_test_aliases-cpp26: using import std
magic_enum_module_test_wchar_t-cpp26: using import std
-- Configuring done (2.9s)
-- Generating done (0.0s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/magic_enum/build
ln -sf build/compile_commands.json .
ninja -C build
ninja: Entering directory `build'
[46/46] Linking CXX executable example/example_module_usage
ninja -C build test
ninja: Entering directory `build'
[0/1] Running tests...
Test project /Users/clausklein/Workspace/cpp/magic_enum/build

No tests were found!!! <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

cmake --install build
-- Install configuration: "Release"
-- Installing: /Users/clausklein/.local/lib/libmagic_enum.a
-- Installing: /Users/clausklein/.local/share/cmake/magic_enum/magic_enumConfig.cmake
-- Installing: /Users/clausklein/.local/share/cmake/magic_enum/magic_enumConfig-release.cmake
bash-5.3$ 

[ClausKlein]

Please check this too:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8b81506..3afa26d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.22...4.4)
 
 if(MAGIC_ENUM_USE_MODULES AND CMAKE_VERSION VERSION_LESS "3.28")
   message(FATAL_ERROR "MAGIC_ENUM_USE_MODULES requires CMake >= 3.28")
@@ -87,9 +87,9 @@ if(MAGIC_ENUM_USE_MODULES)
      CMAKE_CXX_MODULE_STD)
     message("${name}: using import std")
     target_compile_features(${name} PRIVATE cxx_std_23)
-    target_compile_definitions(${name} PRIVATE MAGIC_ENUM_USE_STD_MODULE)
+    set_property(TARGET ${name} PROPERTY CXX_MODULE_STD ON)
+    target_compile_definitions(${name} PUBLIC MAGIC_ENUM_USE_STD_MODULE)
   endif()
-
   set(_scope PUBLIC)
 else()
   add_library(${name} INTERFACE)
@@ -97,6 +97,8 @@ else()
 endif()
 
 add_library(${EXPORT_NAMESPACE}${name} ALIAS ${name})
+
+# TODO: should only be needed for INTERFACE library
 target_include_directories(
   ${name} ${_scope} $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>

[Neargye]

@ClausKlein
What about separating the targets? Keep magic_enum::magic_enum as header-only and make magic_enum::magic_enum_module for modules?
Like fmt fmt::fmt-module

[ClausKlein]

@ClausKlein What about separating the targets? Keep magic_enum::magic_enum as header-only and make magic_enum::magic_enum_module for modules?

That is the question boost, beman, and other projects have a lot of discussions about.

see boostorg/cmake#105

IMHO: Yes, the fmt project does this also!

I dit it here at ClausKlein/asio#5

and I use:

set_target_properties(asio PROPERTIES VERIFY_INTERFACE_HEADER_SETS ${PROJECT_IS_TOP_LEVEL})