1494726 - Malformed top-level await expression lead to confusing error

Status: RESOLVED FIXED

(DevTools :: Console, defect, P1)

Description

[Nicolas Chevobbe [:nchevobbe]]

**Steps to reproduce**

1. Open the console
2. Evaluate `await new Promise())`


**Expected results**

I get the same error as when I only type `Promise())`: `SyntaxError: unexpected token: ')'`

**Actual results**

The following error is displayed: `SyntaxError: await is only valid in async functions and async generators`

---

The error is very confusing since we should now support top-level await.

Comment 1

[Nicolas Chevobbe [:nchevobbe]]

Attachment: Bug 1494726 - Add a test for malformed top-level await expressions; r=jlast.

When an expression starting with await is not mapped by the parserService,
this means it is malformed. In order to get a meaningful error, we wrap
it in an async iife before evaluatin it so the engine throws the appropriate
error, and not "await is only valid in async functions and async generators".

A test case is added to make sure this works as expected.

Comment 2

[Nicolas Chevobbe [:nchevobbe]]

Parser changes will be on this Github PR, then we'll use this bug to do a "release" and add the mochitest.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/46a48161f428
Add a test for malformed top-level await expressions; r=jlast.

Comment 4

[Razvan Maries]

https://hg.mozilla.org/mozilla-central/rev/46a48161f428