Instantiation of HoistableDeclarations prior to Evaluation

[bmeck]

All HoistableDeclarations are instantiated and available at the time of hooking up bindings:

https://tc39.github.io/ecma262/#sec-moduledeclarationenvironmentsetup (towards the end you can see the list of things that gets hoisted prior to eval)

// a.mjs
// this file never evaluates to any meaningful effect

// it kicks off a circular dep on 'b'
import {b_fn} from './b';

// it exports a hoistable delcaration a_fn, this is setup while graph is instantiating
function a_fn() {return b_fn();};
export {a_fn};

// b.mjs
import assert from 'assert';

// grabs 'a'
import {a_fn} from './a';


// it exports a hoistable delcaration b_fn, this is setup while graph is instantiating
const v = {};
function b_fn() {
  return v;
}
export {b_fn};

// evaluation of this line happens before 'a' starts evaluating
// a_fn successfully is called since it was setup during instantiation
assert.strictEqual(a_fn(), v);

The hoistable declarations can also be part of a special form of export default.

[jdalton]

Thanks @bmeck!

Can you explain what the current behavior is and what the expected result is?

[bmeck]

the strictEqual should pass. v passes through a_fn even though a.mjs has not evaluated yet. all hoistable declarations are allocated prior to beginning evaluation of the ESM graph.

[jdalton]

Just to clarify b.mjs should be exporting b_fn right?

Pulling in @benjamn on this since I believe it would be interesting for Reify too.

[bmeck]

@jdalton yes, both are exporting prior to evaluating

[jdalton]

Cleaning up the issue a bit to remove off topic non-@std/esm implementation bits.
I've got this working locally. The fix is to register setters before the module's compile function is called so that they're available when running the compiled module.

[jdalton]

Fixed by ca9716b. Tests 44811ef.