Cannot use EXPORT_ES6=1 and USE_PTHREADS=1 at the same time

[protango]

If I try to invoke emcc using both the EXPORT_ES6 and USE_PTHREADS flags, I receive an error relating to the acorn optimizer:

Command
emcc file.cpp -o bin/file.js --bind -s MODULARIZE=1 -s EXPORT_ES6=1 -O3 -s USE_PTHREADS=1

Output

C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:2780
  throw err
  ^

SyntaxError: 'import' and 'export' may only appear at the top level (61:6)
      import(e.data.urlOrBlob).then(function(PhysicsModule) {
      ^

    at Parser.pp$4.raise (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:2778:13)
    at Parser.pp$1.parseStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:831:16)
    at Parser.pp$1.parseBlock (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:1145:23)
    at Parser.pp$1.parseStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:825:34)
    at Parser.pp$1.parseIfStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:965:26)
    at Parser.pp$1.parseStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:814:31)
    at Parser.pp$1.parseBlock (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:1145:23)
    at Parser.pp$1.parseTryStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:1041:21)
    at Parser.pp$1.parseStatement (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:818:32)
    at Parser.pp$1.parseBlock (C:\emsdk\upstream\emscripten\third_party\acorn\dist\acorn.js:1145:23) {
  pos: ?[33m2136?[39m,
  loc: Position { line: ?[33m61?[39m, column: ?[33m6?[39m },
  raisedAt: ?[33m2142?[39m
}
emcc: error: 'C:/emsdk/node/12.9.1_64bit/bin/node.exe C:\emsdk\upstream\emscripten\tools\acorn-optimizer.js C:\...\bin\physics.worker.js minifyWhitespace' failed (1)

Looks like it is complaining about this line in the outputted "bin/file.worker.js" file:

      import(e.data.urlOrBlob).then(function(Module) {
        return Module.default(Module);
      }).then(function(instance) {
        Module = instance;
        postMessage({ 'cmd': 'loaded' });
      });

[kripken]

This may be a bug in acorn, but more likely either our emitted code is wrong or we need to upgrade it.

[kuhlmannmarkus]

Same here...

[kripken]

#11435 upgraded acorn, and is in emsdk install tot so that might be worth trying.

If that doens't fix it, then as the tags say, we'd be happy to help someone that has time to look into this. Starting by reading the emitted code might be a good starting point. Let us know if you have emscripten-specific questions we can help with, if someone looks at it.

[kuhlmannmarkus]

#11435 unfortunately did not solve the issue.

[RReverser]

I'm running into this as well. Acorn has dynamic import support since 7.0.0, and Emscripten already uses 7.3.1, so on that side of things it's already progressed far enough since the issue was opened.

However, dynamic import is a feature of ES2020 and #11435 - the last update - only set ecmaVersion to 2018. It will need to be bumped again for this to work.

Also note that in Acorn 8.0.0 we have added ecmaVersion: "latest" support for cases where caller just wants all the latest features and doesn't care about specific target. Not sure if Emscripten falls into this category of clients, but if it does, might be worth bumping to it instead.

[sbc100]

Also note that in Acorn 8.0.0 we have added ecmaVersion: "latest" support for cases where caller just wants all the latest features and doesn't care about specific target. Not sure if Emscripten falls into this category of clients, but if it does, might be worth bumping to it instead.

I think we would want that that as long as acorn didn't introduce new language constructs. As of today we still output ES5 and we wouldn't want anything more recent to sneak into the output. Assuming acorn won't do this I think using "latest" here is fine.

[RReverser]

I think we would want that that as long as acorn didn't introduce new language constructs. As of today we still output ES5 and we wouldn't want anything more recent to sneak into the output.

I'm not sure what you mean by that. Acorn is just a parser, so it can gain support for new language constructs, but it can't output or generate anything.

[RReverser]

Btw, I saw this comment too when searching for ecmaVersion:

emscripten/tools/building.py

Lines 1005 to 1006 in 270f795

	# Keep in sync with ecmaVersion in tools/acorn-optimizer.js
	args += ['--language_in', 'ECMASCRIPT_2018']

If we change Acorn to latest, then that one can similarly be set to ECMASCRIPT_NEXT.