A question about code generating by `core/rebuild_async_stubs.js`

[Hajime-san]

When I tried to locally implement an op function with 14 arguments in deno/ext, and the build failed due to the argument limit imposed by core/rebuild_async_stubs.js.
Looking at the contents of core/rebuild_async_stubs.js, it looks like the function is defined each time depending on the number of arguments.
Is there a reason why this can't be replaced by using rest parameters (...theArgs) as shown below?

function setUpAsyncStub(opName, originalOp) {
  const fn = function async_op(...theArgs) {
    const id = nextPromiseId;
    try {
      const maybeResult = originalOp(id, ...theArgs);
      if (maybeResult !== undefined) {
        return PromiseResolve(maybeResult);
      }
    } catch (err) {
      ErrorCaptureStackTrace(err, async_op);
      return PromiseReject(err);
    }
    if (isLeakTracingEnabled) {
      submitLeakTrace(id);
    }
    nextPromiseId = (id + 1) & 0xffffffff;
    return setPromise(id);
  };

  ObjectDefineProperty(fn, "name", {
    value: opName,
    configurable: false,
    writable: false,
  });
  return fn;
}

deno_core/core/00_infra.js

Lines 193 to 236 in 7258aa3

	function setUpAsyncStub(opName, originalOp) {
	let fn;
	// The body of this switch statement can be generated using the script above.
	switch (originalOp.length - 1) {
	/* BEGIN TEMPLATE setUpAsyncStub */
	/* DO NOT MODIFY: use rebuild_async_stubs.js to regenerate */
	case 0:
	fn = function async_op_0() {
	const id = nextPromiseId;
	try {
	const maybeResult = originalOp(id);
	if (maybeResult !== undefined) {
	return PromiseResolve(maybeResult);
	}
	} catch (err) {
	ErrorCaptureStackTrace(err, async_op_0);
	return PromiseReject(err);
	}
	if (isLeakTracingEnabled) {
	submitLeakTrace(id);
	}
	nextPromiseId = (id + 1) & 0xffffffff;
	return setPromise(id);
	};
	break;
	case 1:
	fn = function async_op_1(a) {
	const id = nextPromiseId;
	try {
	const maybeResult = originalOp(id, a);
	if (maybeResult !== undefined) {
	return PromiseResolve(maybeResult);
	}
	} catch (err) {
	ErrorCaptureStackTrace(err, async_op_1);
	return PromiseReject(err);
	}
	if (isLeakTracingEnabled) {
	submitLeakTrace(id);
	}
	nextPromiseId = (id + 1) & 0xffffffff;
	return setPromise(id);
	};
	break;

[bartlomieju]

We benchmarked it and using rest argument was way slower.

As a side note: using 14 arguments might not be the best idea. Consider using and array to "group" some arguments together.

[Hajime-san]

Thanks to you I have resolved my doubts!

Consider using and array to "group" some arguments together.

Good to hear. I will use it as a reference.👀