Post Link for libraries

[ErikSom]

We use --post-link in our build script to do the heavy lifting of compiling Box2D and our glue only once into a bare WASM and then do the cheap part creating a JS library multiple times (ESM / CommonJS).
However a release after 3.1.73 broke --post-link for us. The use-case for libraries might not have been considered with the changes. We now trigger the following error:

if len(options.input_files) != 1:
exit_with_error('--post-link requires a single input file')

This is the command we use to build:
https://github.com/Birch-san/box2d3-wasm/blob/0a839337b041e1de851fc7be9e9a6aae6e4edc4e/box2d3-wasm/shell/1_build_wasm.sh#L143

Any suggestions for us on how to work around the issue, or do you see a way our use case could be considered?

[Birch-san]

we compile box2d and our glue code to bare wasm like so (this is the slow part, and bare wasm means we only have to do it once):

emcc -lembind \
./csrc/glue.cpp \
./csrc/threading.cpp \
./csrc/debugDraw.cpp \
./enkiTS/src/TaskScheduler.cpp \
./cmake-build-deluxe/src/libbox2dd.a \
-I ./box2d/include \
-I ./enkiTS/src \
-I ./box2cpp/include \
-std=c++20 \
-s MODULARIZE=1 \
-s EXPORT_NAME=Box2D \
-s ALLOW_TABLE_GROWTH=1 \
-s FILESYSTEM=0 \
-s EXPORTED_FUNCTIONS=_malloc,_free \
-s ALLOW_MEMORY_GROWTH=1 \
-msimd128 -msse2 -pthread \
-s USE_PTHREADS=1 \
-s PTHREAD_POOL_SIZE=pthreadCount \
-g3 -gsource-map \
-s ASSERTIONS=2 \
--oformat=bare \
-o ./build/Box2D.deluxe.bare.wasm

we then post-link Box2D.deluxe.bare.wasm like so:

emcc \
-g3 -gsource-map -pthread \
-s USE_PTHREADS=1 \
-s PTHREAD_POOL_SIZE='_emscripten_num_logical_cores()' \
-lembind \
-s ALLOW_MEMORY_GROWTH=1 \
--post-link ./build/Box2D.deluxe.bare.wasm \
-s EXPORT_ES6=1 \
-o ./build/dist/es/deluxe/Box2D.deluxe.mjs \
--emit-tsd ./build/dist/es/deluxe/Box2D.deluxe.d.ts

this used to work in 3.1.73, but now fails (e.g. in 4.0.8), as Erik demonstrated above.

[Birch-san]

looks like arg parsing failed? -s options got parsed as positional arguments?

[Birch-san]

you can reproduce in VSCode debugger via:

{
    "configurations": [
        {
            "name": "emcc",
            "type": "debugpy",
            "request": "launch",
            "program": "emcc.py",
            "args": [
                "-g3", "-gsource-map", "-pthread",
                "-s", "USE_PTHREADS=1",
                "-s", "PTHREAD_POOL_SIZE='_emscripten_num_logical_cores()'",
                "-lembind",
                "-s", "ALLOW_MEMORY_GROWTH=1",
                "--post-link", "/Users/birch/git/box2d3-wasm/box2d3-wasm/build/Box2D.deluxe.bare.wasm",
                "-s", "EXPORT_ES6=1",
                "-o", "/Users/birch/git/box2d3-wasm/box2d3-wasm/build/dist/es/deluxe/Box2D.deluxe.mjs",
                "--emit-tsd",
                "/Users/birch/git/box2d3-wasm/box2d3-wasm/build/dist/es/deluxe/Box2D.deluxe.d.ts",
            ],
            "console": "integratedTerminal"
        }
    ]
}

it fails during parsing so you don't even need the files on your computer in order to repro

[sbc100]

Wow, that looks very wrong.

One temporary workaround might be to merge your -s flags in to single arguments like -sALLOW_MEMORY_GROWTH rather than specifying the -s separately. This is the recommended form these days anyway.

Also you can drop USE_PTHREADS=1 since that is implied by -pthread.

Also, for boolean options like -sALLOW_MEMORY_GROWTH there is no need for the extra =1 on the end.