[3.8] [BUG] TLA top-level await breaks with parenthesis

[trusktr]

TypeScript Version: 3.8.1-rc

Search Terms:

Code

// works:
const DBService = await import('./DBService')
await DBService.start()

// doesn't work
await (await import('./DBService')).start()
await (1 + 1)

// works:
async function foo() {
 await (await import('./DBService')).start()
}

export {}

Expected behavior:

no error on the await word

Actual behavior:

TS thinks it is an identifier.

Playground Link:

Playground link

Related Issues:

#35276

[rbuckton]

This is a consequence of how we parse source files and determine whether they are a Module or a Script based on the presence or absence of import or export declarations. According to the TLA proposal, await is now treated like a keyword at the top level of a Module, but not a Script. The fact that await p (without parens) works at the top level currently is actually due to the fact we would parse it as an AwaitExpression for error reporting purposes (and still do for await in a normal function).

To address this, we will likely need to "reparse" a function call whose expression is an await and replace it with an AwaitExpression in any top-level position.

[rbuckton]

We are discussing the details necessary to make this work, but it may depend on changes to our AST Node Factory API proposed in #35282