Destructured promise result in {#await} becomes undefined during re-render

[jesseskinner]

Describe the bug
Values in a destructured promise result become undefined after a re-render.

<script>
	let test = 0;

	$: promise = Promise.resolve({ data: 1 });
</script>

{#await promise then { data }}
	{#if data}
		<button on:click={() => (test = 1)}>Test</button>
	{:else}data is {data}{/if}
{/await}

For some reason, having promise defined in a reactive statement was necessary here to reproduce the bug. In my project, I was calling a function in the {#await} block and passing it a store value.

Logs
N/A

To Reproduce
https://svelte.dev/repl/3fd4e2cecfa14d629961478f1dac2445?version=3.29.0

Expected behavior
I would expect promise results to persist between renders.

Stacktraces
N/A

Information about your Svelte project:

• Your browser and the version: (e.x. Chrome 52.1, Firefox 48.0, IE 10)
  Chrome, Firefox

• Your operating system: (e.x. OS X 10, Ubuntu Linux 19.10, Windows XP, etc)
  Arch Linux

• Svelte version (Please check you can reproduce the issue with the latest release!)
  3.29.0

• Whether your project uses Webpack or Rollup
  N/A

Severity
This is annoying, but I can avoid using destructuring here to get around the problem.

Additional context
N/A

[jesseskinner]

@Conduitry I've added a pull request that seems to fix this bug.

[hdJerry]

I think the undefined is because data can't just be accessed since a Promise is involved.

[jesseskinner]

@hdJerry I fixed it with my pull request, though. Once the promise resolves, the data should remain available.

[hdJerry]

cool, because I tried something using setTimeout and anytime I click the button the value of data continues to increase

[hdJerry]

is data suppose to increase by one?
just curious.

[jesseskinner]

@hdJerry I think what you're seeing there is the return value of setTimeout, which returns an incremented timeout index to be used with clearTimeout.

[hdJerry]

How did you solve it?
I really love svelte.

[jesseskinner]

@hdJerry I actually coded it live on Twitch, if you're interested in watching: https://youtu.be/_7nKfgke29U

[hdJerry]

sweet!!, I will check now.