Pointer to EM_JS function won't compile with MAIN_MODULE

[arseneyr]

Compiling the following file:

#include <emscripten.h>

EM_JS(void, foo, (), {});

void(*foo_ptr)() = &foo;

with emcc test.c -sMAIN_MODULE results in the following error:

Traceback (most recent call last):
  File "/emsdk/upstream/emscripten/emcc.py", line 4309, in <module>
    sys.exit(main(sys.argv))
  File "/usr/lib/python3.10/contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "/emsdk/upstream/emscripten/emcc.py", line 4302, in main
    ret = run(args)
  File "/emsdk/upstream/emscripten/emcc.py", line 1319, in run
    phase_post_link(options, state, wasm_target, wasm_target, target)
  File "/usr/lib/python3.10/contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "/emsdk/upstream/emscripten/emcc.py", line 3022, in phase_post_link
    phase_emscript(options, in_wasm, wasm_target, memfile)
  File "/usr/lib/python3.10/contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "/emsdk/upstream/emscripten/emcc.py", line 3052, in phase_emscript
    emscripten.run(in_wasm, wasm_target, final_js, memfile)
  File "/emsdk/upstream/emscripten/emscripten.py", line 893, in run
    emscript(in_wasm, out_wasm, outfile_js, memfile)
  File "/emsdk/upstream/emscripten/emscripten.py", line 341, in emscript
    assert imp.kind == webassembly.ExternType.FUNC
AssertionError

I'm not sure if this is a bug or just a construct that is not allowed during dynamic linking. If it's the latter, perhaps the error message should be improved.

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.28 (f11d6196dd4e8748a726f19895c859b40ff6a4f3)
clang version 16.0.0 (https://github.com/llvm/llvm-project ea4be70cea8509520db8638bb17bcd7b5d8d60ac)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /emsdk/upstream/bin

[kripken]

@sbc100 I think you recently got EM_ASM working but EM_JS is still a TODO?

[sbc100]

This is the main module (where EM_JS and EM_ASM have always worked), not the side module.

Notably the problem goes away if I do -sMAIN_MODULE=2 (which is highly recommended).

Investigating more.