Destructuring with fallback and then reassigning in `{#each}` is broken

[wackbyte]

Describe the bug

In non-runes mode, destructuring an object with a fallback and then assigning to that variable in a callback does not seem to mutate it.

When the button is clicked in the REPL, this is the output:

1 false
2 false

It should be:

1 false
2 true

Reproduction

REPL

Logs

No response

System Info

REPL, Svelte 5.0.5, Firefox iOS

Severity

annoyance

[7nik]

In Svelte 4 it doesn't work either.
In the runes mode, you get the each_item_invalid_assignment error on x = true.

[brunnerh]

This seems like a bit of an edge case.
At least the state updates if actually stored somewhere.

[wackbyte]

Note that it works as expected if you don't have a fallback: REPL

[7nik]

Destructuring with fallback internally is done as derived and I assume it doesn't see changes because the array isn't stateful. Defining it with a variable will make it coarsely reactive - the change will be propagated only in the next tick.
If you make the array deeply reactive, it will work.

[dummdidumm]

Could you provide a more complete code example that better resembles your use case? As others pointed out, this doesn't work in Svelte 4 either, so I'm having a hard time to understand what is actually broken between 4 and 5 - if this is related to a 4->5 discrepancy at all.