Error in system/lib/libcxx/include/optional when _LIBCPP_STD_VER < 20

[SaraBaradaran]

I faced the following error when compiling cpputest (https://github.com/cpputest/cpputest) using Emscripten. It seems there is a bug in system/lib/libcxx/include/optional when _LIBCPP_STD_VER < 20.

version: latest and even 3.1.54

/home/sara/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1/optional:419:16: error: type name requires a specifier or qualifier
  419 |         ::new ((void*)_VSTD::addressof(this->__val_)) value_type(_VSTD::forward<_Args>(__args)...);
      |                ^
/home/sara/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1/optional:419:23: error: expected ')'
  419 |         ::new ((void*)_VSTD::addressof(this->__val_)) value_type(_VSTD::forward<_Args>(__args)...);
      |                       ^
/home/sara/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1/__config:848:17: note: expanded from macro '_VSTD'
  848 | #  define _VSTD std
      |                 ^
/home/sara/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1/optional:419:15: note: to match this '('
  419 |         ::new ((void*)_VSTD::addressof(this->__val_)) value_type(_VSTD::forward<_Args>(__args)...);
      |

You can reproduce the error using the following commands:

$ git clone https://github.com/cpputest/cpputest
$ cd cpputest/build
$ emcmake cmake ..
$ emmake cmake --build .

[sbc100]

Emscripten uses the libc++ headers from the latest stable llvm release. That means we are currently including the libc++ headers from llvm 17. Its likely that this issue is an upstream issue with llvm 17. Is there some way you could try building that library with libc++-17 to confirm this?

[SaraBaradaran]

Emscripten uses the libc++ headers from the latest stable llvm release. That means we are currently including the libc++ headers from llvm 17. Its likely that this issue is an upstream issue with llvm 17. Is there some way you could try building that library with libc++-17 to confirm this?

Thanks for your response. I compiled the same project using emscripten version 3.1.41 which uses libc++ headers from llvm 16 and it could build the project without introducing any errors. So, this seems to be an issue related to headers from llvm 17.

[sbc100]

Let see if this bug is fixed when we update the llvm headers: #21530