[svelte 5]: value should be assigned and cleared here

[frederikhors]

Describe the bug

I'm trying Svelte 5 for the first time today.

This is a reproduction of this issue.

PLEASE USE CHROME since Firefox does not emit onchange event.

As you can see if I select a date from the picker the {value} is not assigned and the same if I press the "Clear" button.

Why?

Severity

blocking an upgrade

[F2]

Just chipping in... I agree it seems to be a regression.

It seems to be related to the same prop being assigned the same value from two different components.

Here is a smaller example with runes.
And here is the same example without runes.
Both are failing in Svelte 5.
When you click the button, myProp is updated but the component is never re-rendered.

Putting the last example into Svelte 4 works fine.

[machak]

Here is a smaller example with runes.

using bind:myProp={myProp} fixes the issue

[frederikhors]

using bind:myProp={myProp} fixes the issue

Yeah. But this is a workaround.

[dummdidumm]

I believe the minimum reproduction is this. It seems that a derived value getting read, then another dependency triggering a rerun which results in the same value, and then a render effect reading the derived falsely makes that render effect believe nothing has changed. The other reproductions use props in a way that trigger the hardest variant of the internal props function, which uses derived in a certain way.