feat: Add C++ modules support by mikomikotaishi · Pull Request #1530 · brainboxdotcc/DPP

mikomikotaishi · 2025-12-27T11:45:58Z

This pull request adds support for C++20 modules.

In order to accomplish this, some constants were changed to using external linkage.

~~I have also updated nlohmann/json to version 3.12.0, as the older version declares some symbols as internal.~~ Updating nlohmann/json has been moved to #1596.

Code change checklist

I have ensured that all methods and functions are fully documented using doxygen style comments.
My code follows the coding style guide.
I tested that my change works before raising the PR.
I have ensured that I did not break any existing API calls.
I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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Mishura4

Thanks for the PR! Good stuff. Just gonna prefer the approach with including dpp.h in the module for maintainability, as discussed in https://discord.com/channels/825407338755653642/825411104208977952/1454456223952011427

braindigitalis

some module related unit tests would be good. not repeating a thousand lines of code in dpp.cppm is an absolute must, as @Mishura4 also said.

mikomikotaishi · 2025-12-27T20:21:50Z

I've looked at the src/unittest/ files but I'm not particularly familiar with how you've set up the unit testing framework. Are you just looking to run those same tests under import dpp; rather than #include <dpp/dpp.h>?

braindigitalis · 2025-12-27T22:48:21Z

I think that in this case you might want to make a new .cpp under the unittests folder which imports dpp instead of #including it. it can have some test functions that are exported and called via standard approaches from the main unittest file.

mikomikotaishi · 2025-12-28T09:13:47Z

I think this should fix the errors we're encountering. It's with the build system configuration

braindigitalis · 2025-12-28T13:18:42Z

you cant just do -DDPP_MODULES=ON for the entire CI matrix. Some CI's use older g++ (which we support) and some use C++17.

mikomikotaishi · 2025-12-28T17:25:19Z

Then is it possible to disable the modules unit tests for C++17 CI tests?

mikomikotaishi · 2025-12-29T01:01:20Z

@braindigitalis I think the modules CI should just be in a totally separate CI. It requires Ninja, as CMake can't build modules with Makefiles.

braindigitalis · 2025-12-29T08:22:13Z

unit tests only run in one g++, which is g++-12. This is the one which is packaged. we cant and dont run unit tests on them all, as the unit tests connect to discord and we cant do this concurrently.

Jaskowicz1 · 2025-12-29T12:22:44Z

Updated Title to match code standards

Mishura4

Example doesn't seem to build on Windows. Can we add it to CI somehow?
Also, please fix merge conflicts.

Mishura4 · 2026-07-18T16:32:53Z


+set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -rdynamic")
+
+# Create gcm.cache directory and symlink to the main build's dpp.gcm


Yes I can see that, but why?

Clang obtains the BMI paths through -fprebuilt-module-path which indicates where to scan, but GCC has no such option, and places its BMIs in gcm.cache/, which is why the lookup location is populated with the symlink to the actual interface.

Why is this necessary? I've not had to do this with any of my other projects

Jaskowicz1

A couple comments, nothing to really reject for though

Jaskowicz1 · 2026-08-24T20:05:04Z

ngl i'm pretty happy with moving to clang-cl for windows lol

github-actions Bot added documentation Improvements or additions to documentation build Issue or Pull Request related to the build process code Improvements or additions to code. labels Dec 27, 2025

Jaskowicz1 requested review from Jaskowicz1, Mishura4 and braindigitalis December 27, 2025 11:57

Jaskowicz1 added the enhancement New feature or request label Dec 27, 2025

mikomikotaishi force-pushed the dev branch 3 times, most recently from e91eaa8 to 121eb9b Compare December 27, 2025 12:04

Mishura4 requested changes Dec 27, 2025

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mikomikotaishi force-pushed the dev branch 3 times, most recently from 1909f3f to 7f6fb23 Compare December 28, 2025 06:06

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Comment thread docpages/example_code/using_modules.cpp Outdated

Comment thread docpages/example_programs/misc/using_modules.md Outdated

Comment thread docpages/example_code/using_modules.cpp Outdated

mikomikotaishi force-pushed the dev branch from 7f6fb23 to 50e6ec1 Compare December 29, 2025 01:07

mikomikotaishi force-pushed the dev branch from 50e6ec1 to 9cd8ccc Compare December 29, 2025 10:51

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Jaskowicz1 changed the title ~~Add C++ modules support and update nlohmann::json~~ feat: Add C++ modules support and update nlohmann::json Dec 29, 2025

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Comment thread src/unittest/test.cpp

mikomikotaishi force-pushed the dev branch from 3f278f0 to 531227d Compare July 10, 2026 17:52

Add a static-linux and install-consumer job on CI

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mikomikotaishi force-pushed the dev branch from 491f882 to d887c03 Compare July 10, 2026 19:35

mikomikotaishi added 2 commits July 10, 2026 15:36

Merge branch 'dev' into dev

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Merge branch 'dev' into dev

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Comment thread .github/workflows/ci.yml

Merge branch 'dev' into dev

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Merge branch 'dev' into dev

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Comment thread docpages/example_code/using_modules.cpp Outdated

Comment thread docpages/example_programs/misc/using_modules.md

Comment thread include/dpp/etf.h Outdated

Apply recommended docs changes

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mikomikotaishi force-pushed the dev branch from d42e053 to ac09477 Compare July 19, 2026 04:24

Add a CI for building the module on Windows

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Comment thread docpages/include/modules_warn.dox Outdated

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mikomikotaishi added 2 commits July 25, 2026 15:44

Merge branch 'dev' into dev

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Merge branch 'dev' into dev

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mikomikotaishi force-pushed the dev branch from 09f96e5 to c4dcd94 Compare August 9, 2026 20:24

Fix reported issues by maintainers

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mikomikotaishi force-pushed the dev branch from c4dcd94 to 294146b Compare August 9, 2026 21:46

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Comment thread docpages/example_code/CMakeLists.txt

Explicitly disable GNU extensions

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mikomikotaishi force-pushed the dev branch from fa337ce to 9f0e908 Compare August 23, 2026 19:22

Use ClangCL instead of cl.exe, due to error C2039

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mikomikotaishi force-pushed the dev branch from 9f0e908 to 54bcd73 Compare August 23, 2026 20:01

Jaskowicz1 reviewed Aug 24, 2026

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Comment thread docpages/example_code/CMakeLists.txt

Clarify CMake instructions for modules

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Merge branch 'dev' into dev

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		set (CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -rdynamic")

		# Create gcm.cache directory and symlink to the main build's dpp.gcm

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