Prepare CXX_MODULE usage #286

ClausKlein · 2026-01-16T17:22:39Z

This is a prototype only to evaluate some concepts how we can work with CXX_MODULES

I added 3 cmake modules which can be included before and after project() call.

include(cmake/prelude.cmake)
project(...)
include(cxx-modules-rules)
if(BEMAN_HAS_MODULES)
Require C++20 or newer with extensions for modules!
target_compile_definitions(beman.exemplar PUBLIC BEMAN_HAS_MODULES)
target_compile_features(beman.exemplar PUBLIC cxx_std_${CMAKE_CXX_STANDARD})
endif()
include(beman-install-library-config) # Local fix only to install modules right!

All 3 are prepared to be integrated / merged into `infra/cmake` repo

They add 3 new global options:

BEMAN_HAS_MODULES:BOOL=ON
BEMAN_USE_STD_MODULE:BOOL=OFF
BEMAN_HAS_IMPORT_STD::BOOL=${CMAKE_CXX_SCAN_FOR_MODULES} # only if toolchain supports it.

Create a self contained `CXX_MODULE`

Add module usage example too that will be tested after staged install to build directory

8fbd480 Set BEMAN_USE_STD_MODULE=1 on gcc presets
76afe1e Disable BEMAN_USE_STD_MODULE for now
bb7b274 Add option BEMAN_USE_STD_MODULE
a77018c Disable CI tests with clang and libstdc++ for now
eb59178 Disable CI tests with gcc-13 for now
f1e4627 Add generic cmake modules to work with import std;
5afc6ca On UNIX Ninja is required to build CXX_MODULES
f0cb4e7 Require C++20 or newer with extensions for modules
83ddc05 Try to handle CI matrix complexity
fcd47ab Update googletest to v1.17.0 (reverted again)
0abf4a9 Modules opt in only on compilers that support it
0768b67 Use ctest --build-and-test to check the installed version
a4f2313 rm CMakeUserPresets.json (accidentally added)
18d3e51 Prepare CXX_MODULE usage

Local fix only to install modules right!
Need to define the default / minimum CMAKE_CXX_STANDARD value (17 or 20)!
some historic compiler should not longer used / supported!
install test on CI should not longer needed?
Cookiecutter is a nightmare, next week I will start to try

It depends on following PR:

fix #287 too

Add module usage example too Create a self contained CXX_MODULE Fix modules install path

coveralls · 2026-01-16T17:26:28Z

coverage: 100.0%. remained the same
when pulling 802d221 on ClausKlein:feature/add_cxx_module
into 57fd7e9 on bemanproject:main.

ClausKlein · 2026-01-18T17:55:06Z

@ednolan Please help, I can't fix some of the CI problems caused by infra structure

I disabled on CI C++26 tests with historic appleclang, gcc-13, clang-17, clang-18

ClausKlein · 2026-01-21T09:25:04Z

@ednolan I disable the gcc-13 tests on CI for now

see ticket #290

and C++26 is not usable with apple clang, see #289

eb59178

to "Check if import std; is possible"

cmake/cxx-modules-rules.cmake

ClausKlein · 2026-01-21T20:38:09Z

How it works internally:

/Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release
bash-5.3$ tree stagedir/
stagedir/
├── bin
│   ├── beman.exemplar.examples.identity_as_default_projection
│   ├── beman.exemplar.examples.identity_direct_usage
│   ├── beman.exemplar.examples.identity_module_usage
│   └── beman.exemplar.tests.identity
├── include
│   └── beman
│       └── exemplar
│           └── identity.hpp
└── lib
    ├── cmake
    │   └── beman.exemplar
    │       ├── beman.exemplar-config-version.cmake
    │       ├── beman.exemplar-config.cmake
    │       ├── beman.exemplar-targets-relwithdebinfo.cmake
    │       ├── beman.exemplar-targets.cmake
    │       ├── cxx-modules
    │       │   ├── cxx-modules-beman.exemplar-RelWithDebInfo.cmake
    │       │   ├── cxx-modules-beman.exemplar.cmake
    │       │   └── target-exemplar-RelWithDebInfo.cmake
    │       └── modules
    │           └── identity.cppm
    └── libbeman.exemplar.a

10 directories, 14 files
bash-5.3$ ninja
[4/4] Linking CXX executable stagedir/bin/beman.exemplar.tests.identity
ld: warning: ignoring duplicate libraries: 'lib/libgtest.a'
bash-5.3$ ctest
Test project /Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release
    Start 1: IdentityTest.call_identity_with_int
1/9 Test #1: IdentityTest.call_identity_with_int ......................   Passed    0.01 sec
    Start 2: IdentityTest.call_identity_with_custom_type
2/9 Test #2: IdentityTest.call_identity_with_custom_type ..............   Passed    0.01 sec
    Start 3: IdentityTest.compare_std_vs_beman
3/9 Test #3: IdentityTest.compare_std_vs_beman ........................   Passed    0.01 sec
    Start 4: IdentityTest.check_is_transparent
4/9 Test #4: IdentityTest.check_is_transparent ........................   Passed    0.01 sec
    Start 5: install-to-stagedir
5/9 Test #5: install-to-stagedir ......................................   Passed    0.05 sec
    Start 6: find-package-test
6/9 Test #6: find-package-test ........................................   Passed    2.74 sec
    Start 7: beman.exemplar.examples.identity_direct_usage
7/9 Test #7: beman.exemplar.examples.identity_direct_usage ............   Passed    0.30 sec
    Start 8: beman.exemplar.examples.identity_module_usage
8/9 Test #8: beman.exemplar.examples.identity_module_usage ............   Passed    0.24 sec
    Start 9: beman.exemplar.examples.identity_as_default_projection
9/9 Test #9: beman.exemplar.examples.identity_as_default_projection ...   Passed    0.24 sec

100% tests passed, 0 tests failed out of 9

Total Test time (real) =   3.62 sec
bash-5.3$ !tree
tree stagedir/
stagedir/
├── bin
│   ├── beman.exemplar.examples.identity_as_default_projection
│   ├── beman.exemplar.examples.identity_direct_usage
│   ├── beman.exemplar.examples.identity_module_usage
│   └── beman.exemplar.tests.identity
├── include
│   └── beman
│       └── exemplar
│           └── identity.hpp
└── lib
    ├── cmake
    │   └── beman.exemplar
    │       ├── beman.exemplar-config-version.cmake
    │       ├── beman.exemplar-config.cmake
    │       ├── beman.exemplar-targets-relwithdebinfo.cmake
    │       ├── beman.exemplar-targets.cmake
    │       ├── cxx-modules
    │       │   ├── cxx-modules-beman.exemplar-RelWithDebInfo.cmake
    │       │   ├── cxx-modules-beman.exemplar.cmake
    │       │   └── target-exemplar-RelWithDebInfo.cmake
    │       └── modules
    │           └── identity.cppm
    └── libbeman.exemplar.a

10 directories, 14 files
bash-5.3$ cd -
/Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release/tests/beman/exemplar/find-package-test
bash-5.3$ ninja
ninja: no work to do.
bash-5.3$ ctest
Test project /Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release/tests/beman/exemplar/find-package-test
    Start 1: beman.exemplar.examples.identity_direct_usage
1/3 Test #1: beman.exemplar.examples.identity_direct_usage ............   Passed    0.23 sec
    Start 2: beman.exemplar.examples.identity_module_usage
2/3 Test #2: beman.exemplar.examples.identity_module_usage ............   Passed    0.23 sec
    Start 3: beman.exemplar.examples.identity_as_default_projection
3/3 Test #3: beman.exemplar.examples.identity_as_default_projection ...   Passed    0.28 sec

100% tests passed, 0 tests failed out of 3

Total Test time (real) =   0.75 sec
bash-5.3$ cmake -L .
-- use ccache
CMake Warning at /Users/clausklein/Workspace/cpp/beman-project/exemplar/cmake/prelude.cmake:46 (message):
  $CXX is not set
Call Stack (most recent call first):
  CMakeLists.txt:5 (include)


-- CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES=/usr/local/Cellar/gcc/15.2.0/include/c++/15;/usr/local/Cellar/gcc/15.2.0/include/c++/15/x86_64-apple-darwin23;/usr/local/Cellar/gcc/15.2.0/include/c++/15/backward;/usr/local/Cellar/gcc/15.2.0/lib/gcc/current/gcc/x86_64-apple-darwin23/15/include;/usr/local/Cellar/gcc/15.2.0/lib/gcc/current/gcc/x86_64-apple-darwin23/15/include-fixed;/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include;/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/System/Library/Frameworks
-- CMAKE_CXX_SCAN_FOR_MODULES=ON
Examples to be built: identity_direct_usage;identity_module_usage;identity_as_default_projection
-- Configuring done (0.1s)
CMake Warning (dev) in CMakeLists.txt:
  CMake's support for `import std;` in C++23 and newer is experimental.  It
  is meant only for experimentation and feedback to CMake developers.
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Generating done (0.0s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release/tests/beman/exemplar/find-package-test
-- Cache values
BEMAN_HAS_MODULES:BOOL=ON
BEMAN_USE_STD_MODULE:BOOL=OFF
CCACHE_EXECUTABLE:FILEPATH=/usr/local/bin/ccache
CMAKE_BUILD_TYPE:STRING=RelWithDebInfo
CMAKE_CXX_COMPILER_LAUNCHER:PATH=/usr/local/bin/ccache
CMAKE_C_COMPILER_LAUNCHER:PATH=/usr/local/bin/ccache
CMAKE_INSTALL_PREFIX:PATH=/Users/clausklein/.local
CMAKE_MAKE_PROGRAM:FILEPATH=/Users/clausklein/.local/bin/ninja
CMAKE_OSX_ARCHITECTURES:STRING=
CMAKE_OSX_DEPLOYMENT_TARGET:STRING=
CMAKE_OSX_SYSROOT:STRING=
beman.exemplar_DIR:PATH=/Users/clausklein/Workspace/cpp/beman-project/exemplar/build/gcc-release/stagedir/lib/cmake/beman.exemplar
bash-5.3$

Prepare CXX_MODULE usage

18d3e51

Add module usage example too Create a self contained CXX_MODULE Fix modules install path

ClausKlein requested review from bretbrownjr, camio, dietmarkuehl, ednolan, neatudarius, steve-downey and wusatosi as code owners January 16, 2026 17:22

ClausKlein marked this pull request as draft January 16, 2026 21:18

ClausKlein added 6 commits January 16, 2026 23:15

rm CMakeUserPresets.json

a4f2313

Use ctest --build-and-test to check the installed version

0768b67

Modules opt in only on compilers that support it

0abf4a9

Update googletest to v1.17.0

fcd47ab

Try to handle CI matrix complexity

83ddc05

Require C++20 or newer with extensions for modules

f0cb4e7

On UNIX Ninja is required to build CXX_MODULES

5afc6ca

ClausKlein mentioned this pull request Jan 18, 2026

Install FILE_SET CXX_MODULES too bemanproject/infra#13

Open

ClausKlein added 3 commits January 18, 2026 20:52

Quickfix: use CMAKE_GENERATOR name

d8f7d5c

Add generic cmake modules to work with import std;

f1e4627

Disable CI tests with gcc-13 for now

eb59178

ClausKlein added 2 commits January 21, 2026 10:47

Disable CI tests with clang and libstdc++ for now

a77018c

Add option BEMAN_USE_STD_MODULE

bb7b274

to "Check if import std; is possible"

ClausKlein commented Jan 21, 2026

View reviewed changes

cmake/cxx-modules-rules.cmake Show resolved Hide resolved

ClausKlein added 2 commits January 21, 2026 18:35

Disable BEMAN_USE_STD_MODULE for now

76afe1e

Set BEMAN_USE_STD_MODULE=1 on gcc presets

8fbd480

ClausKlein self-assigned this Jan 21, 2026

ClausKlein added 2 commits January 21, 2026 23:20

Fix typos and cleanup presets

978c132

Change the scope of the used guards

802d221

ClausKlein marked this pull request as ready for review January 22, 2026 16:12

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Prepare CXX_MODULE usage #286

Prepare CXX_MODULE usage #286

Uh oh!

ClausKlein commented Jan 16, 2026 •

edited

Loading

Uh oh!

coveralls commented Jan 16, 2026 •

edited

Loading

Uh oh!

ClausKlein commented Jan 18, 2026 •

edited

Loading

Uh oh!

ClausKlein commented Jan 21, 2026 •

edited

Loading

Uh oh!

Uh oh!

ClausKlein commented Jan 21, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Prepare CXX_MODULE usage #286

Are you sure you want to change the base?

Prepare CXX_MODULE usage #286

Uh oh!

Conversation

ClausKlein commented Jan 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

This is a prototype only to evaluate some concepts how we can work with CXX_MODULES

Require C++20 or newer with extensions for modules!

All 3 are prepared to be integrated / merged into infra/cmake repo

Create a self contained CXX_MODULE

Add module usage example too that will be tested after staged install to build directory

It depends on following PR:

Uh oh!

coveralls commented Jan 16, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

ClausKlein commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

ClausKlein commented Jan 21, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

ClausKlein commented Jan 21, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

ClausKlein commented Jan 16, 2026 •

edited

Loading

All 3 are prepared to be integrated / merged into `infra/cmake` repo

Create a self contained `CXX_MODULE`

coveralls commented Jan 16, 2026 •

edited

Loading

ClausKlein commented Jan 18, 2026 •

edited

Loading

ClausKlein commented Jan 21, 2026 •

edited

Loading