Template Instantiation Error in system/lib/libcxx/include/__memory/pointer_traits.h

[SaraBaradaran]

I faced the following error when compiling proxy (https://github.com/microsoft/proxy) using Emscripten. It seems there is a bug in system/lib/libcxx/include/__memory/pointer_traits.h header.

version: latest and even 3.1.54

/home/sara/emsdk/upstream/emscripten/cache/sysroot/include/c++/v1/__memory/pointer_traits.h:118:22: error: implicit instantiation of undefined template 'std::__pointer_traits_element_type<std::nullptr_t>'
  118 |     typedef typename __pointer_traits_element_type<pointer>::type    element_type;
      |                      ^

You can reproduce the error using the following commands:

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

[sbc100]

Our C++ headers come from clang's libc++. Do you happen to know if this issue also occurs with libc++? You can try this by building using -stdlib=libc++.

If this is an issue was was already fixes in libc++ then this could be fixed when #21530 is fixed