fix(14815): warn when an invalid <select multiple> value is given

[GauBen]

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Emit a warning instead of crashing the runtime when an invalid value is provided

Closes #14815

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[Rich-Harris]

preview: https://svelte-dev-git-preview-svelte-14816-svelte.vercel.app/

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[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@14816

[paoloricciuti]

Overall is good...however we recently switched to let TS handle this kind of typing issues so maybe we can just prevent the fail without throwing the warning.

In this case it's a bit different tho because this will be a much more descriptive error... I'll let some other maintainer with more experience decide on this 😁

[paoloricciuti]

I'm pretty sure this has performance implications...I don't know why it was written this way tho

[GauBen]

If we want better (theoretical) performance, we should use neither .indexOf nor .includes (code will be O(select.options.length * value.length)) but rewrite it as

const values = new Set(value);
for (var option of select.options) {
  option.selected = values.has(get_option_value(option));
}

which is now O(select.options.length + value.length)

We'll see what perf addicts say of this 👀

[GauBen]

Includes is fast! https://www.measurethat.net/Benchmarks/Show/6029/0/some-vs-filter-vs-indexof-vs-includes

[paoloricciuti]

Why this change?

[GauBen]

It doesn't make much sense to have a templated function that does not use nor restrict its type parameter, it can be replaced with any. Asking for unknown[] makes it more type-safe, // @ts-ignore is no longer required.

[GauBen]

Thanks for the review @paoloricciuti!

For consistency, I'd say that <select multiple value={null / undefined}> should be accepted and ignored, like how other properties behave when given a nullish value. Regarding non-array values, TS can do the trick, we can hard-crash on them.