[WIP] Avoid creating wrapper thunks or wasm exports

[sbc100]

In debug builds nothing really changes here since we exported functions still get statically assigned to debug wrappers/thunks.

However, after this change, in release builds, if you attempt to access _foo (internally) or Module['_foo'] externally before the module is loaded you will now get undefined.

Since it was always the case that calling these function would crash anyway, the only effected folks would be folks that take the reference early and then call later. e.g.

var myfunc = Module['_foo'];  // Run before module is loaded
// wait until loaded
myfunc();  // This will no longer work.

Fixes: #23339

[sbc100]

Maybe this new behaviour should be behind -sSTRICT to avoid breaking folks?

[sbc100]

Or perhaps I can introduce a warning when folks do this, and let that cook for a few releases first?

[sbc100]

Marking as draft for now

[brendandahl]

It seems like if we do this, then debug builds should behave in a similar way. i.e. if you take a reference to a not ready function then that function should never work.

// Before the wasm module is loaded
var myFoo = Module['foo'];
Module['onRuntimeInitialized'] = () => {
  myFoo(); // <<< should not work in debug or opt builds
};

[sbc100]

It seems like if we do this, then debug builds should behave in a similar way. i.e. if you take a reference to a not ready function then that function should never work.

// Before the wasm module is loaded
var myFoo = Module['foo'];
Module['onRuntimeInitialized'] = () => {
  myFoo(); // <<< should not work in debug or opt builds
};

Yes that is correct. The only difference I would propose is that maybe we can make the debug builds fail in a nicer way than the release builds:

• release build: attempt to call undefined
• debug build: abort("call to myFoo reference taken before module is ready")

That way at least we help the folks who were previously relying on this.

However, I'm not totally sure it worth breaking anybody here, which is why I marked this as a draft. Do many folks do you think would be broken if that above code (which works today) stops working?

[brendandahl]

I feel like most the code I've seen people usually call through the module object, but I've mainly looked at g3 code. We could try testing this in g3 too.

At least if it does break someone, the error is not a subtle one and should be relatively easy to fix.