fix: improve ssr code generation for class property $derived

[trueadm]

Fixes #10643.

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[brunnerh]

This looks like it removes memoization, which could still be relevant if the value is used in multiple places and is expensive to compute.

[trueadm]

This looks like it removes memoization, which could still be relevant if the value is used in multiple places and is expensive to compute.

Can you provide an example?

[brunnerh]

Before, the value was set in a field once, hence it only got computed once.
Now it gets computed on every get.

	class Counter {
		count = 0;
-		doubled = this.count * 2;
+		get doubled() {
+			return this.count * 2;
+		}

		constructor(initialCount = 0) {
			this.count = initialCount;
		}
	}

[trueadm]

@brunnerh I think this should be fine in all likelihood. It wasn't that the value was being memoized before, it was just always static and never changed. So if you changed this.state, then doubled would never get updated – which was a major bug. If we were to bring in memoization again then we'd need invalidation for when it's changed, which means adding a lot more logic into the SSR runtime.

[brunnerh]

A static value is a form of memoization.

Couldn't the assignment of all derived fields just be moved to the end of the constructor?

(Also, I would not even bother using $derived if it weren't for its memoization, so that being gone in SSR is not good.)

[trueadm]

@brunnerh Nice call. #10661