Svelte: Undefined error when using a destructured variable

[ghost]

Describe the bug
When trying to render a child component Svelte will think that a destructured variable is undefined when another export ... statement comes after the destructuring.

Logs
In the example code given below you should see the error:

bar is not defined

when the baz export is at the bottom of the <script> and you should see it fixed when the baz export is moved to the top.

To Reproduce
Create a SubCom.svelte and add this code:

<p>{bar}</p>

<script>
export let foo
const { bar } = foo

export let baz
</script>

Now in App.svelte add this code:

<h1>Syntax related error</h1>

<SubCom {foo} {baz} />

<script>
import SubCom from './SubCom.svelte'

const foo = { bar: 1 }
const baz = {}
</script>

You should see the error.

To fix the error just change SubCom.svelte to:

<p>{bar}</p>

<script>
export let baz
export let foo
const { bar } = foo
</script>

Expected behavior
I expect both versions to work.

Severity
Not high, since it's easy to work around.

You could also fix by removing the destructuring syntax.

[paymonsattar]

I have also come across this problem. Although not a big issue as you can simply move the export... statement up it would be good to have it work regardless.

[Conduitry]

This will be fixed by #3539.

[Conduitry]

Fixed by #3539, test added in #3722.