Emscripten toolchain should point to cache sys root about corrade HOT 4 CLOSED

After applying this change, you might run into issues with implicit C headers being included by the C++ compiler. Those headers are not in system/include, but they are in cache/sysroot/include.

The fix can be found in emscripten-core/emscripten#17137, the important part:

if("${CMAKE_C_IMPLICIT_INCLUDE_DIRECTORIES}" STREQUAL "")
  set(CMAKE_C_IMPLICIT_INCLUDE_DIRECTORIES "${EMSCRIPTEN_SYSROOT}/include")
endif()
if("${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES}" STREQUAL "")
  set(CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES "${EMSCRIPTEN_SYSROOT}/include")
endif()

This makes sure that explicitly adding the cache sysroot include doesn't have preference over the implicit C++ include directory.

from corrade.

Ah, yes, thanks for the reminder.

There's still the problem with headers/libraries of 3rd party projects installed into Emscripten sysroot getting stale that I didn't have time to investigate further, which is why I didn't merge this patch yet. But, just yesterday, while working on the cursed issues from mosra/magnum#560 I was browsing Emscripten changelog and found this in 2.0.24:

CMake projects (those that either use emcmake or use Emscripten.cmake directly) are new configured to install (by default) directly into the emscripten sysroot. This means that running cmake --install (or running the install target, via make install for example) will install resources into the sysroot such that they can later be found and used by find_path, find_file, find_package, etc. Previously the default was to attempt to install into the host system (e.g /usr/local) which is almost always not desirable. Folks that were previously using CMAKE_INSTALL_PREFIX to build their own secondary sysroot may be able to simplify their build system by removing this completely and relying on the new default.

Yes, we're not using the upstream toolchain, so it doesn't affect us, but what I consider important about this note is that upstream treats installing into Emscripten's own sysroot as the recommended practice. Which means that either they should hopefully know about this potential "stale" issue and having a builtin solution for it (that I'm not aware of yet), or the toolchain handles that somehow (and because we don't use it, we don't have that handled), or there might at least be some issues open about this. I'll try to look back into this when I get time.

from corrade.

Closing as resolved, forgot this issue was even here.

Just for the record, the first patch was integrated with various version-dependent modification as mosra/toolchains@d5d7430, and the toolchains submodule was updated in 45282f8. The second patch seems to be not needed -- looking into CMake's CMakeFiles/<version>/CMakeCXXCompiler.cmake in the build dir, the CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES already contains it, together with others. I suppose CMake extracts it via emcc -E -v - as it already does for other compilers.

This is for example with CMake 3.17 and Emscripten 2.0.25 on the CI, the sysroot include dir is last:

set(CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES "/emsdk/upstream/emscripten/cache/sysroot/include/SDL;/emsdk/upstream/emscripten/cache/sysroot/include/compat;/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1;/emsdk/upstream/lib/clang/13.0.0/include;/emsdk/upstream/emscripten/cache/sysroot/include")

from corrade.

Eh, in the end I actually did hit a similar problem, although in my case I had to add the non-cache include dir there: mosra/toolchains@6a9e082

Because FindZstd installed into the non-cache location (because otherwise it wouldn't be able to locate its libraries, because THE DAMN THING copies only contents of include/ but not lib/, EXCEPT FOR lib/cmake/, so I can't even put the CMake configs into lib/cmake/ but have to move them into share/cmake/ instead, as otherwise again it would be copied together with its includes but not libraries) otherwise added the non-cache include dir into the include path, resulting in an eventual error due to including the wrong doomed-to-fail <emscripten/version.h>.

I hate everything about this platform. Everything.

from corrade.