@embroider/macros babel plugin: Optional chaining expression gets aggressively optimized to undefined

[ArnaudWeyts]

Summary

While upgrading to Embroider in our main app, I noticed that the babel plugin for @embroider/macros transpiles code like aKnownValue?.foo to undefined prematurely.

Steps to reproduce

I created a repo here which showcases the issue: https://github.com/ArnaudWeyts/embroider-macros-reproduction

What happens is the following:

const aKnownValue = {};
aKnownValue.foo = true;
console.log(aKnownValue?.foo);

gets transpiled into

const aKnownValue = {};
aKnownValue.foo = true;
console.log(undefined);

We have several places in our codebase where this optional chaining is applied, and it's currently blocking us from upgrading to Embroider since it seems like Embroider makes this babel plugin run on all the source code while it didn't before.

I tried to pinpoint why this was happening but it seems like this is currently happening by design, as I noticed there's a test that makes sure this works:

embroider/packages/macros/tests/babel/eval.test.ts

Lines 35 to 38 in e55b055

	test('optional chaining nullish member access', () => {
	let code = transform(`const result = knownUndefinedValue?.x;`);
	expect(code).toMatch(`result = undefined`);
	});

Other pointers that I discovered:

• Exact place where the code is replaced:

  embroider/packages/macros/src/babel/macros-babel-plugin.ts

  Line 250 in acb8c6f

  path.replaceWith(buildLiterals(result.value, context));

• The evaluator that returns a "confident" undefined:

  embroider/packages/macros/src/babel/evaluate-json.ts

  Lines 156 to 169 in f41229b

  	return {
  	confident: true,
  	get value() {
  	if (optionalChain) {
  	return confidentObject.value != null
  	? confidentObject.value[confidentProperty.value]
  	: confidentObject.value;
  	} else {
  	return confidentObject.value[confidentProperty.value];
  	}
  	},
  	hasRuntimeImplementation:
  	confidentObject.hasRuntimeImplementation || confidentProperty.hasRuntimeImplementation,
  	};

If anyone could help me give some pointers as what exactly needs to happen, I can look into creating a PR, but I'm not really sure where this issue should be fixed.

Thanks for working on this project!