Raise recoverable error for await expressions in sync functions

[sosukesuzuki]

Q	A
Fixed Issues?	Fixes #12436, closes #11090
Patch: Bug Fix?	Y
Tests Added + Pass?	Yes
License	MIT

This PR addresses only await problem, not yield.

[babel-bot]

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[nicolo-ribaudo]

We can probably avoid the lookahead by moving this logic to the end of this function: after calling parseUpdate(), it it returns an identifier whose name is await, we can check if it could be an await expression and the call parseAwait().

parseAwait() then needs to be modified to accept the startLoc and startPos parameters (we can get .start and .loc.start from parseUpdate's result), and call startNodeAt instead of startNode in parseAwait.

[sosukesuzuki]

e16250c

[nicolo-ribaudo]

Oh I found #11090 - I completely forgot about it so thanks for opening a new PR!

Something that I notice is missing from this PR is support for TLA: when the plugin is enabled, it we are parsing a script and there is a top-level await expression, we can report an error.

[sosukesuzuki]

Something that I notice is missing from this PR is support for TLA: when the plugin is enabled, it we are parsing a script and there is a top-level await expression, we can report an error.

1affea3

[sosukesuzuki]

@JLHwung Thank you for your reviews. I fixed reviewed points!

[nicolo-ribaudo]

I wonder why this is reported twice 🤔

[sosukesuzuki]

This is because the error is raised in duplicate with checkReserved.

babel/packages/babel-parser/src/parser/expression.js

Lines 2349 to 2355 in 6e69209

	if (!this.prodParam.hasAwait && word === "await") {
	this.raise(
	startLoc,
	this.hasPlugin("topLevelAwait")
	? Errors.AwaitNotInAsyncContext
	: Errors.AwaitNotInAsyncFunction,
	);

I've fixed with workaround by adding a set called invalidAwaitErrors to state at 6d3b9c5. Is there better way?

[nicolo-ribaudo]

Thanks!

[nicolo-ribaudo]

I tweaked the PR title a bit to make it fit the max commit title length shown by GitHub

[JLHwung]

We are throwing different errors for

async function foo() {
  function bar(x = await 2) {}
}