(void*) cast required in val.h about emscripten

[sbc100]

Are you trying to use val.h under gcc? In general I would assume that emscripten headers are only compatible with the version of clang that we support.

[sparlist]

This fails when using clang compiler as well.

Compiler:-

Apple clang version 15.0.0 (clang-1500.1.0.2.5)
Target: x86_64-apple-darwin23.2.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Error:-

/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:239:20: error: assigning to 'void *' from 'const char *' discards qualifiers
239 | cursor->w[0].p = wt;
| ^~

[sbc100]

Hmm.. I wonder why we don't see that in emscripten.. since we use clang. Perhaps because its a system header and the rules are more lax?

Did you run into this while trying to use val.h outside of the context of emscripten?

[sbc100]

Can you share the exact command line you used to get that error using clang? I can't seem to reproduce it.

[sparlist]

Build Script:-

#!/bin/sh

# Set the local build directory
build=".wasm"

# Make the directory; generate the makefiles; make & install
mkdir -p $build && cd $build && \
emcmake cmake .. > /dev/null 2>&1

# If the cmake failed, try once more with a clean build directory clean
if [ $? != 0 ]; then
    cd .. && rm -rf $build && \
    mkdir -p $build && cd $build && \
    emcmake cmake ..
fi

# Now make
emmake make -j4 all

CMakeLists.txt:-

cmake_minimum_required(VERSION 3.20)
project(XXXXX-WASM CXX)

set (CMAKE_CXX_STANDARD 17)

set(SOURCES
    xxxxx.cpp
    ....
    yyyyy.cpp
)

set(LIBNAME xxxxx)

add_compile_options(-O3 -fPIC)

add_executable(${LIBNAME} ${SOURCES})

set_target_properties(${LIBNAME} PROPERTIES LINK_FLAGS "-Os -s DEMANGLE_SUPPORT=1 -s ALLOW_MEMORY_GROWTH=1 --bind")

[sbc100]

So does the warning show up when using emcc ? i.e. when you do emmake make?

[sbc100]

Oh I see, I probably have to instantiate the writeGenericWireType template in some way. Perhaps that is what I'm missing? How do you using embind in order to get the warning to trigger?

[sparlist]

yes - it fails at the 'emmake make -j4 all' stage

[sbc100]

@brendandahl do you think you know how to write a repro for this one?

[sparlist]

Here's the full error context:-

/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:239:20: error: assigning to 'void *' from 'const char *' discards qualifiers
  239 |   cursor->w[0].p = wt;
      |                    ^~
/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:261:3: note: in instantiation of function template specialization 'emscripten::internal::writeGenericWireType<const char>' requested here
  261 |   writeGenericWireType(cursor, BindingType<First>::toWireType(std::forward<First>(first)));
      |   ^
/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:269:5: note: in instantiation of function template specialization 'emscripten::internal::writeGenericWireTypes<const char *&>' requested here
  269 |     writeGenericWireTypes(cursor, std::forward<Args>(args)...);
      |     ^
/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:640:27: note: in instantiation of member function 'emscripten::internal::WireTypePack<const char *&>::WireTypePack' requested here
  640 |     WireTypePack<Args...> argv(std::forward<Args>(args)...);
      |                           ^
/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:517:12: note: in instantiation of function template specialization 'emscripten::val::internalCall<emscripten::internal::EM_METHOD_CALLER_KIND::FUNCTION, bool, (lambda at /Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/val.h:518:7), const char *&>' requested here
  517 |     return internalCall<EM_METHOD_CALLER_KIND::FUNCTION, ReturnValue>(
      |            ^
/Users/xxxxx/tmp/emsdk/upstream/emscripten/cache/sysroot/include/emscripten/bind.h:1246:24: note: in instantiation of function template specialization 'emscripten::val::call<bool, const char *&>' requested here
 1246 |         return wrapped.call<ReturnType>(name, std::forward<Args>(args)...);
      |                        ^
/Users/xxxxx/yyyyy/zzzzz.cpp:19:59: note: in instantiation of function template specialization 'emscripten::wrapper<xxx:YYYYYY>::call<bool, const char *&>' requested here
   19 |     virtual bool WantXXXXX(const char* name) { return call<bool>("wantXXXXX", name); }

[brendandahl]

val.call doesn't accept const char* as arguments. Use either val("some str") or std::string.