Project fails to configure in cmake since i updated emsdk to 6.0.6

[Honya2000]

Hello,

My project depends on or_tools third party project, which has those lines in cmake:

set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
set(THREAD_PREFER_PTHREAD_FLAG TRUE)
find_package(Threads REQUIRED)

The thing is I do not need threads (threads aren't enabled in my root CMakeLists.txt).
So I absolutely have no idea how this was working before. It was just working about 2 years so I didn't ask questions...

But now it fails:

CMake Error at C:/Program Files/CMake/share/cmake-3.30/Modules/FindPackageHandleStandardArgs.cmake:233 (message):
Could NOT find Threads (missing: Threads_FOUND)
Call Stack (most recent call first):
C:/Program Files/CMake/share/cmake-3.30/Modules/FindPackageHandleStandardArgs.cmake:603 (_FPHSA_FAILURE_MESSAGE)
C:/Program Files/CMake/share/cmake-3.30/Modules/FindThreads.cmake:226 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
third_party/or_tools/cmake/system_deps.cmake:17 (find_package)
third_party/or_tools/CMakeLists.txt:450 (include)

Yesterday everything was fine. Since yesterday i just upgraded Python from 3.10.0 to 3.10.11 and emsdk to 6.0.6 (do not remember exactly which version was before, probably 6.0.4).

I doubt Python broke Threads setup in cmake.

Is anything were changed in emsdk regarding Threads setup with disabled pthreads recently ?

P.S. It's not just or_tools. Tried to disable Threads in or_tools:
if (NOT EMSCRIPTEN)
find_package(Threads REQUIRED)
endif()

But it fails in many other projects. For example Abseil also fails with the same error.

[Honya2000]

Reverted to 6.0.5 and now everything is working!

[sbc100]

One fairly major change with 6.0.6 was #27469. Taking a look now to see if I can reproduce this.

[sbc100]

Indeed early investigation does point to #27469 (DEFAULT_TO_CXX) being the issue here.

One thing that Gemini noticed here is that THREAD_PREFER_PTHREAD_FLAG is misspelled. There should be an S at the end of the first word here: THREADS_PREFER_PTHREAD_FLAG

[sbc100]

Can you share a link to your full cmake file?

It seems like #27469 caused the issue because the pthread detection mechanism build and links a small C program. Not that its not a C++ program but if you have C++-specific things in your CMAKE_EXE_LINKER_FLAGS, for example, then the pthread detection will fail. Note that I think it would fail in the same way on your native/host target too.

[Honya2000]

Not sure what you mean by full cmake file? You mean root ? Don’t think you can use it because it includes hundreds sub-porojects.

Will try to reproduce it today with simple cmake project depent on or-tools or abseil.

[sbc100]

My current best guess is that you (or some subproject) has added something with C++ dependencies to CMAKE_EXE_LINKER_FLAGS (or some other flag that effects the find_package compiler run.

Perhaps you could attach the cmake log file to show the compiler errors when running find_package(Threads REQUIRED)?

As a workaround you could try adding -sDEFAULT_TO_CXX to your CMAKE_EXE_LINKER_FLAGS