Prepare use of CMAKE_CXX_MODULE_STD by ClausKlein · Pull Request #35 · bemanproject/scope

ClausKlein · 2025-05-31T09:10:06Z

/Users/clausklein/Workspace/cpp/cxx23/scope
bash-5.2$ !CXX
CXX=g++-15 cmake -S . -B build -D CMAKE_CXX_STANDARD=20 -D CMAKE_CXX_MODULE_STD=0 --fresh 
-- The CXX compiler identification is GNU 15.1.0
-- 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: /usr/local/bin/g++-15 - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- CMAKE_CXX_STANDARD="20" ; CMAKE_CXX_SCAN_FOR_MODULES="1" ; CMAKE_CXX_MODULE_STD="0" ; CMAKE_CXX_COMPILER_IMPORT_STD=""
-- Compiler is: GNU version: 15.1.0
-- CMake is: 4.0.2 modules scan: 1
Cloning into 'catch2-src'...
HEAD is now at 2b60af89 v3.8.1
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__ - Success
Examples to be built: scope_example;unique_resource;unique_resource-file
-- Configuring done (16.5s)
-- Generating done (0.1s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/cxx23/scope/build
bash-5.2$ CXX=g++-15 cmake -S . -B build -D CMAKE_CXX_STANDARD=23 -D CMAKE_CXX_MODULE_STD=1 --fresh 
-- The CXX compiler identification is GNU 15.1.0
-- 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: /usr/local/bin/g++-15 - skipped
-- Detecting CXX compile features
CMake Warning (dev) at /usr/local/share/cmake/Modules/Compiler/CMakeCommonCompilerMacros.cmake:248 (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):
  /usr/local/share/cmake/Modules/CMakeDetermineCompilerSupport.cmake:113 (cmake_create_cxx_import_std)
  /usr/local/share/cmake/Modules/CMakeTestCXXCompiler.cmake:83 (CMAKE_DETERMINE_COMPILER_SUPPORT)
  CMakeLists.txt:17 (project)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Detecting CXX compile features - done
-- CMAKE_CXX_STANDARD="23" ; CMAKE_CXX_SCAN_FOR_MODULES="1" ; CMAKE_CXX_MODULE_STD="1" ; CMAKE_CXX_COMPILER_IMPORT_STD="23;26"
-- Compiler is: GNU version: 15.1.0
-- CMake is: 4.0.2 modules scan: 1
Cloning into 'catch2-src'...
HEAD is now at 2b60af89 v3.8.1
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__ - Success
Examples to be built: scope_example;unique_resource;unique_resource-file
-- Configuring done (8.6s)
-- Generating done (0.1s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/cxx23/scope/build

bash-5.2$ cmake --version
cmake version 4.0.2

CMake suite maintained and supported by Kitware (kitware.com/cmake).
bash-5.2$

JeffGarland · 2025-05-31T11:51:04Z

CMakeLists.txt

+    set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
+        "d0edc3af-4c50-42ea-a356-e2862fe7a444"
+    )
+    set(CMAKE_CXX_STANDARD 26)


In discussions at c++now about this we made the decision that we weren't setting the standard in our cmake so as to not override the user options. If the library requires a certain level well that needs to be check in header and cause compile failure. That's the better approach since a user might just lift this code and not use our cmake at all

JeffGarland · 2025-05-31T11:56:39Z

CMakeLists.txt

 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+# TODO(CK): set(CMAKE_CXX_MODULE_STD 1)
+if(CMAKE_CXX_MODULE_STD)
+    set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD


In case it isn't clear from the other PR, I removed all aspirations of using import std; for the moment -- I'm really only trying to get to import beman.scope; right now. For which, the claim is non of this is needed. That said happy to experiment here...

After pulling your branch locally -- I commented out all of this section and it still works with clang-20 and g++15

JeffGarland · 2025-05-31T12:06:40Z

Regardless of my commentary above -- I've confirmed this actually works on g++15 and clang++20. And we have modules lift-off? Let's see how far we can take this...

tests/module.test.cpp

JeffGarland · 2025-05-31T15:52:44Z

.github/workflows/ci_tests.yml

        compilers:
          - class: GNU
-            version: 14
+            version: 15


so I pulled this change into my branch, but it looks like we need a change to the test container because it's unable to find gcc-15

We don't have testing container up for gcc-15 yet.
No package managers for ubuntu 24.04 ships it for now.
This is high priority to me, but if anyone want to work on it please do.
See: bemanproject/infra#18

CMakeLists.txt

wusatosi · 2025-05-31T18:20:40Z

.github/workflows/ci_tests.yml

        uses: lukka/get-cmake@latest
        with:
-          cmakeVersion: "~3.25.0"
+          cmakeVersion: "~4.0.0"


Is there a reason we use inconsistent CMake version here

Is there a reason we use inconsistent CMake version here

we need a newer version of cmake than 3.25 for modules -- needs to be 3.28 at least to work with 'named modules'. 4.x might well be required to support import std;

wusatosi · 2025-05-31T18:21:20Z

CMakeLists.txt

+    set(CMAKE_CXX_STANDARD_REQUIRED OFF)
+endif()
+
+cmake_minimum_required(VERSION 3.28...4.0)


as previously discussed, no upper bound for cmake version requirement.

wusatosi · 2025-05-31T18:21:57Z

tests/CMakeLists.txt

+    SYSTEM
+    # FIXME: FIND_PACKAGE_ARGS 3.8.1


What is this?

ClausKlein · 2025-06-01T03:04:49Z

This works on CI see: https://github.com/ClausKlein/scope/actions/runs/15398118700

wusatosi · 2025-06-01T04:03:04Z

This works on CI except for g++-15: https://github.com/ClausKlein/scope/actions/runs/15366704399

gcc 15 is not distrbuted in any package managers... We can ignore it before we have our own infra to deploy them

ClausKlein · 2025-06-01T21:17:37Z

I have no time to rebase 3 times a day!

But I can wait until you finish your exploration.

We need at least cmake v3.28! We need to set CMAKE_CXX_SCAN_FOR_MODULES too! Fix compiler program name for apple-clang Prevent unintended define of HAS_STDLIB_MODULES Make it more readable The final cleanup Prepare run-clang-tidy too

CMakeLists.txt

JeffGarland · 2025-06-06T00:10:51Z

So here's what I'd like to do with this PR. Can we split it into 2? The first one would be for a new issue to update presets and clang-tidy. That way we can just approve that stuff and merge it to main. It's only barely related to the modules work.

The second part would be for experimental import std support. Since that seems like it's in an extremely experimental state w.r.t. compilers and cmake I'm thinking we should keep that that on a branch and document that if people want to play with it they should use that branch. That's breaking some new ground, but it might be a nice way to push the envelope while keeping main focused on what works now. Thoughts?

ClausKlein · 2025-06-06T05:24:05Z

I will remove the accidentally added presets (which need cmake 3.30),
but is seem we need to use cmake_minimum_required(VERSION 4.0)

Too this is only valid for on CMake minor version:

# valid only for cmake version 4.0.x
        set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD
            "a9e1cf81-9932-4810-974b-6eccaf14e457"
        )

ClausKlein · 2025-06-06T11:38:24Z

But I have still problems with build tests on OSX:

bash-5.2$ ninja -C build examples/all 
ninja: Entering directory `build'
ninja: warning: build log version is too old; starting over
[19/19] Linking CXX executable examples/unique_resource

bash-5.2$ ninja -C build all_verify_interface_header_sets 
ninja: Entering directory `build'
[1/1] Building CXX object CMakeFiles/beman.scope_verify_interface_header_sets.dir/beman.scope_verify_interface_header_sets/beman/scope/scope.hpp.cxx.o

bash-5.2$ ninja -C build all -k 1
ninja: Entering directory `build'
[237/237] Linking CXX executable tests/test.module
FAILED: tests/test.module tests/test.module-b12d07c_tests.cmake /Users/clausklein/Workspace/cpp/cxx23/scope/build/tests/test.module-b12d07c_tests.cmake 
: && /usr/local/bin/g++-15  -Wl,-search_paths_first -Wl,-headerpad_max_install_names  tests/CMakeFiles/test.module.dir/module.test.cpp.o -o tests/test.module  _deps/catch2-build/src/libCatch2Main.a  libbeman.scope.a  _deps/catch2-build/src/libCatch2.a && cd /Users/clausklein/Workspace/cpp/cxx23/scope/build/tests && /usr/local/bin/cmake -D TEST_TARGET=test.module -D TEST_EXECUTABLE=/Users/clausklein/Workspace/cpp/cxx23/scope/build/tests/test.module -D TEST_EXECUTOR= -D TEST_WORKING_DIR=/Users/clausklein/Workspace/cpp/cxx23/scope/build/tests -D TEST_SPEC= -D TEST_EXTRA_ARGS= -D "TEST_PROPERTIES=SKIP_RETURN_CODE;4" -D TEST_PREFIX= -D TEST_SUFFIX= -D TEST_LIST=test.module_TESTS -D TEST_REPORTER= -D TEST_OUTPUT_DIR= -D TEST_OUTPUT_PREFIX= -D TEST_OUTPUT_SUFFIX= -D TEST_DL_PATHS= -D TEST_DL_FRAMEWORK_PATHS= -D CTEST_FILE=/Users/clausklein/Workspace/cpp/cxx23/scope/build/tests/test.module-b12d07c_tests.cmake -D ADD_TAGS_AS_LABELS=FALSE -P /Users/clausklein/Workspace/cpp/cxx23/scope/build/_deps/catch2-src/extras/CatchAddTests.cmake
Undefined symbols for architecture x86_64:
  "initializer for module std", referenced from:
      __static_initialization_and_destruction_1() in module.test.cpp.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.
bash-5.2$

davidhunter22 · 2025-09-29T03:05:42Z

I would like to suggest a further possible split in these changes.
Split the changes based on what a user wants if they want to include the headers of this library but use import std in their code.
This is based on similar changes I have suggested for the GSL, Guidelines Support Library, at microsoft/GSL#1217
This would mean changing one file, scope.h to be the following, no other changes required

#if defined(HAS_STDLIB_MODULES)
    import std;
#else
    #include <concepts>
    #include <exception>
    #include <type_traits>
    #include <version>
    #include <limits>
#endif

Why?
Well it allows consumers of the current header to immediately try using import std without waiting for this project to sort out every detail of how Cmake, and other stuff, is going to work. Set HAS_STDLIB_MODULES import the standard library module, include scope.hpp, and your good to go.
By the way HAS_STDLIB_MODULES used in this way would probably be to generic a name,maybe BEMAN_SCOPE_USE_STD_MODULE but I don't really care.
Note I regard this as the first step in this PR, but it may allow experimentation and use far faster than agreeing everything else.

Oh also I wanted to thank Claus for this PR. I have been a little wary of proposing similar changes to CMake stuff for other libraries and am hoping I can use this as a template. I have noticed in other project that the code changes for import std are often a lot simpler and less contentious than the Cmake changes which is sad!

ClausKlein · 2025-10-01T04:43:07Z

@JeffGarland are you still interrested to merge this PR?

davidhunter22 · 2025-10-01T15:35:32Z

I am keen to get this PR or similar in, let me know if I can help in any way.
I am pushing a similar PR in GSL microsoft/GSL#1218

ClausKlein · 2026-01-27T17:24:24Z

I want to wait until infra repo supports CXX_MODULES and import std; it is on the way.

ClausKlein requested review from JeffGarland, robert-andrzejuk and wusatosi as code owners May 31, 2025 09:10

ClausKlein requested a review from a team May 31, 2025 09:10

JeffGarland reviewed May 31, 2025

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JeffGarland requested a review from nickelpro May 31, 2025 12:10

JeffGarland reviewed May 31, 2025

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ClausKlein marked this pull request as draft May 31, 2025 14:25

ClausKlein force-pushed the feature/use-cxx-module branch from 3572928 to 4b1e959 Compare May 31, 2025 14:34

JeffGarland reviewed May 31, 2025

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wusatosi reviewed May 31, 2025

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tests/CMakeLists.txt

Comment on lines +9 to +10

SYSTEM

# FIXME: FIND_PACKAGE_ARGS 3.8.1

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ClausKlein force-pushed the feature/use-cxx-module branch 2 times, most recently from b8efde2 to 27c2426 Compare May 31, 2025 19:08

ClausKlein marked this pull request as ready for review June 1, 2025 03:05

ClausKlein force-pushed the feature/use-cxx-module branch from 27c2426 to 34e9c54 Compare June 1, 2025 04:02

ClausKlein marked this pull request as draft June 1, 2025 21:16

ClausKlein added 2 commits June 3, 2025 03:45

Prepare use of CMAKE_CXX_MODULE_STD

f6ad07e

We need at least cmake v3.28! We need to set CMAKE_CXX_SCAN_FOR_MODULES too! Fix compiler program name for apple-clang Prevent unintended define of HAS_STDLIB_MODULES Make it more readable The final cleanup Prepare run-clang-tidy too

Apply pre-commit run --all

ae22641

ClausKlein force-pushed the feature/use-cxx-module branch from 130cbc8 to 50efc36 Compare June 3, 2025 02:41

github-actions bot reviewed Jun 3, 2025

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CMakeLists.txt Outdated Show resolved Hide resolved

Run clang-tidy on examples too

30117e8

ClausKlein force-pushed the feature/use-cxx-module branch from 50efc36 to 30117e8 Compare June 3, 2025 02:43

Disable CMAKE_EXPORT_COMPILE_COMMANDS by default

13bb730

Use cmake v4.0.2 on CI

2b89401

ClausKlein force-pushed the feature/use-cxx-module branch from 0d1895f to 2b89401 Compare June 6, 2025 11:26

ClausKlein requested a review from JeffGarland June 6, 2025 11:40

ClausKlein added 2 commits June 6, 2025 15:02

Fix typo

443ac34

Add special cmake hacks for OSX

2c9e2b0

Merge branch '33-module-for-beman-scope' into feature/use-cxx-module

2c90ce6

ClausKlein requested a review from wusatosi October 1, 2025 04:43

Update used SW versions

1eae018

ClausKlein self-assigned this Jan 27, 2026

ClausKlein closed this Jan 27, 2026

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