Effect teardown function not using previous value of a derived

[Kcwidman]

I'm not sure if this is a bug or not, but this is related to this merge request (released 5.23.0).

I have example code and a repl below.

If an effect re-runs because the value of a $derived() changes, the value of the $derived() in the teardown function is the current value. This is different if you replace the $derived() with a $state(). In this latter case, the value of the $state() in the teardown function is the previous value.

As is typical, the wording in the docs is very terse, making it unclear to me whether or not this is a design choice, or a bug. Some insight into this would be much appreciated. Thanks!

repl

<script>
    let v = $state(1)

    const updateVal = () => (v = 2)

    const d = $derived(v)

    $effect(() => {
        console.log("old value derived", v)
        return () => {
            console.log("old value direct", v) // outputs 1 on button click
        }
    })
    $effect(() => {
        console.log("new value derived", d)
        return () => {
            console.log("old value derived", d) // outputs 2  on button click
        }
    })
</script>

<button onclick={updateVal}>click</button>

[brunnerh]

This could be reported as an issue since there is a perceived inconsistency.