breaking: array proxy coercion is no longer reactive in template

[trueadm]

Fixes #13525. An alternative approach to #13541.

Note: this only applies to template effects

This is an interesting one but one I think we need. When you have an object in the template, we push people to use toString() in order for its contents to be reactive – as this shows intent. Today, we have some cases where this is not consistent.

However, we have Symbol.toPrimitive and we can detect this on our proxied arrays and actually intervene and provide a non-reactive result in the case where someone hasn't explicitly called toString() from within the template. This means that we now have better consistency and we can push people to using thing.toString() instead of using coercion. Which are all far better than just having it magically be reactive with coercion.

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[dummdidumm]

Since this only applies to template effects and not deriveds (i.e. $derived('hello '+ array) will still be reactive), should we use a special set-text function for this instead which untracks things? might result in less code and one less flag to worry about.

[trueadm]

Since this only applies to template effects and not deriveds (i.e. $derived('hello '+ array) will still be reactive), should we use a special set-text function for this instead which untracks things? might result in less code and one less flag to worry about.

How would that work? Today we pass in a template literal, are you suggesting we don't use template literals anymore? Actually that's pretty interesting, let me play with that idea more.

[dummdidumm]

I haven't had any concrete thoughts in mind beyond "maybe there's some way", but it seems you now have, so that's cool 😄