WASM/WASI target

[guest271314]

What language does this apply to?
WebAssembly/WASI, and to some extent JavaScript.

Describe the problem you are trying to solve.

I'm trying to compile https://github.com/fails-components/webtransport to WASM using WASI-SDK.

Describe the solution you'd like

WASI-SDK toolchain doesn't have <sys/wait.h> which is referenced in compiler/subprocess.cc, so I'm getting this error

[ 32%] Building CXX object third_party/protobuf/CMakeFiles/libprotoc.dir/src/google/protobuf/compiler/subprocess.cc.obj
clang++: warning: -lwasi-emulated-signal: 'linker' input unused [-Wunused-command-line-argument]
/media/user/1/webtransport/transports/http3-quiche/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc:43:10: fatal error: 'sys/wait.h' file not found
   43 | #include <sys/wait.h>
      |          ^~~~~~~~~~~~
1 error generated.
make[2]: *** [third_party/protobuf/CMakeFiles/libprotoc.dir/build.make:1213: third_party/protobuf/CMakeFiles/libprotoc.dir/src/google/protobuf/compiler/subprocess.cc.obj] Error 1
make[1]: *** [CMakeFiles/Makefile2:5416: third_party/protobuf/CMakeFiles/libprotoc.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

Describe alternatives you've considered

I am not a CMake expert by any means. I changed the original CMakeList.txt to this, because from what I gather from the maintainer protobuf needs to be available on the native system, not compiled to WASM

IF(APPLE)
    set_target_properties(protoc libprotoc libprotobuf PROPERTIES OSX_ARCHITECTURES arm64;x86_64 CACHE STRING "Build architectures for Mac OS X" FORCE )
ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "WASI")
    # Add any specific properties for WASI targets here if needed. 
    # The WASI toolchain usually handles the necessary flags automatically.
    # The original OSX_ARCHITECTURES property is irrelevant for WASI.
    execute_process(
        COMMAND uname -m
        OUTPUT_VARIABLE HOST_ARCH
        OUTPUT_STRIP_TRAILING_WHITESPACE
    )
    set_target_properties(protoc libprotoc libprotobuf
        PROPERTIES
            OSX_ARCHITECTURES "${HOST_ARCH}"
    )
ENDIF()

Next I tried just commenting out the whole subprocess.cc file, and that doesn't work, either.

Additional context
Add any other context or screenshots about the feature request here.

Issue where I try to get roadmap from maintainer, who is not interested in WASM support for their library fails-components/webtransport#354.

[guest271314]

I tried with Emscripten, too. Erroring and exiting around the same place.

emmake make

#...

[ 33%] Linking CXX executable protoc
wasm-ld: error: libprotoc.a(command_line_interface.cc.o): undefined symbol: google::protobuf::compiler::Subprocess::Subprocess()
wasm-ld: error: libprotoc.a(command_line_interface.cc.o): undefined symbol: google::protobuf::compiler::Subprocess::Start(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&, google::protobuf::compiler::Subprocess::SearchMode)
wasm-ld: error: libprotoc.a(command_line_interface.cc.o): undefined symbol: google::protobuf::compiler::Subprocess::Start(std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>> const&, google::protobuf::compiler::Subprocess::SearchMode)
wasm-ld: error: libprotoc.a(command_line_interface.cc.o): undefined symbol: google::protobuf::compiler::Subprocess::Communicate(google::protobuf::Message const&, google::protobuf::Message*, std::__2::basic_string<char, std::__2::char_traits<char>, std::__2::allocator<char>>*)
wasm-ld: error: libprotoc.a(command_line_interface.cc.o): undefined symbol: google::protobuf::compiler::Subprocess::~Subprocess()
em++: error: '/media/user/1/emsdk/upstream/bin/wasm-ld -o protoc-3.21.9.wasm CMakeFiles/protoc.dir/src/google/protobuf/compiler/main.cc.o libprotoc.a libprotobuf.a -L/media/user/1/emsdk/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten -L/media/user/1/emsdk/upstream/emscripten/src/lib -lGL-getprocaddr -lal -lhtml5 -lstubs -lnoexit -lc -ldlmalloc -lcompiler_rt -lc++-noexcept -lc++abi-noexcept -lsockets -mllvm -combiner-global-alias-analysis=false -mllvm -enable-emscripten-sjlj -mllvm -disable-lsr /tmp/tmpufl5smbblibemscripten_js_symbols.so --strip-debug --export=_emscripten_stack_alloc --export=__wasm_call_ctors --export=emscripten_stack_get_current --export=_emscripten_stack_restore --export-if-defined=__start_em_asm --export-if-defined=__stop_em_asm --export-if-defined=__start_em_lib_deps --export-if-defined=__stop_em_lib_deps --export-if-defined=__start_em_js --export-if-defined=__stop_em_js --export-if-defined=main --export-if-defined=__main_argc_argv --export-table -z stack-size=65536 --no-growable-memory --initial-heap=16777216 --no-entry --table-base=1 --global-base=1024' failed (returned 1)
make[2]: *** [third_party/protobuf/CMakeFiles/protoc.dir/build.make:102: third_party/protobuf/protoc-3.21.9.0] Error 1
make[1]: *** [CMakeFiles/Makefile2:5538: third_party/protobuf/CMakeFiles/protoc.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

[guest271314]

A WebAssembly programmer mentioned that protobuf-lite is supported by Emscripten and WASM. I'm not sure how to substitute protobuf-lite for protobuf in the CMakeLists.txt file to test.