Arch Linux

Invoking em++ to compile a simple C++ program with the -Os flag complains that a JavaScript library is missing:

tuankiet65:~/emscripten/ $ em++ -Os hello.cpp
shared:INFO: EM_IGNORE_SANITY set, ignoring sanity checks
em++: warning: unexpected binaryen version: 95 (expected 93) [-Wversion-check]
internal/modules/cjs/loader.js:1068
throw err;
^

Error: Cannot find module 'acorn'
Require stack:
- /usr/lib/emscripten/tools/acorn-optimizer.js
at Function.Module._resolveFilename (internal/modules/cjs/loader.js:1065:15)
at Function.Module._load (internal/modules/cjs/loader.js:911:27)
at Module.require (internal/modules/cjs/loader.js:1125:19)
at require (internal/modules/cjs/helpers.js:75:18)
at Object.<anonymous> (/usr/lib/emscripten/tools/acorn-optimizer.js:1:13)
at Module._compile (internal/modules/cjs/loader.js:1236:30)
at Object.Module._extensions..js (internal/modules/cjs/loader.js:1257:10)
at Module.load (internal/modules/cjs/loader.js:1085:32)
at Function.Module._load (internal/modules/cjs/loader.js:950:14)
at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12) {
code: 'MODULE_NOT_FOUND',
requireStack: [ '/usr/lib/emscripten/tools/acorn-optimizer.js' ]
}
em++: error: '/usr/bin/node /usr/lib/emscripten/tools/acorn-optimizer.js /tmp/emscripten_temp_8pgwloxq/a.out.wasm.o.js AJSDCE minifyWhitespace' failed (1)

At optimization level -O2 and higher, tools/acorn-optimizer.js is used to optimize the output JavaScript file, however this tool depends on the acorn library which is not installed. I temporarily fixed it by manually installing the library using npm, however I think a permanent fix is to install the libraries by running "npm install" or "npm ci" in the tools/ directory. emscripten's formulae for Homebrew does something like that (https://github.com/Homebrew/homebrew-core/blob/master/Formula/emscripten.rb#L80). Emsdk also does invoke npm ci (https://github.com/emscripten-core/emsdk/blob/master/emsdk.py#L1226)