Miscompilation of bind:group when used with a Set

[yamplum]

Describe the bug

When trying to pass a Set to the bind:group directive, I get the following error: value.includes is not a function in App.svelte. Indeed, the correct method to check membership of a Set is has() rather than includes().

Using a Set in a bind:group seems like a natural use case and I didn't catch anything about this limitation in the docs, so I assume it is not intentional. I suspect it should be a relatively easy fix.

Potentially related mention of this(?) issue from 2020: #5721 (comment)

Reproduction

https://svelte.dev/playground/11b978c08eb34f06a499b7dc87e98672?version=5.25.9

I can't verify if it used to work in Svelte 4 because Svelte 4 playground doesn't work (Error compiling component: Unrecognized option 'runes').

Logs

System Info

System:
    OS: macOS 15.3.2
    CPU: (8) arm64 Apple M1
    Memory: 108.41 MB / 8.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 23.11.0 - /opt/homebrew/bin/node
    Yarn: 1.22.22 - /opt/homebrew/bin/yarn
    npm: 10.9.2 - /opt/homebrew/bin/npm
    pnpm: 10.6.5 - /opt/homebrew/bin/pnpm
  Browsers:
    Chrome: 135.0.7049.42
    Safari: 18.3.1
  npmPackages:
    svelte: ^5.0.0 => 5.1.2

Severity

annoyance

[dummdidumm]

bind:group only works with arrays, not sure if we should enhance that

[paoloricciuti]

bind:group only works with arrays, not sure if we should enhance that

But how would that work? Try to check for includes and if it's not there try with has?

[felix-tjernberg]

I also came upon this issue and agree with @yamplum that it would be a nice enhancement as @dummdidumm phrases it

I did "get got" when I tried to look what value was in the source which confused and delighted me xD, however am I correct in that get() being replaced by something after compilation if so where in the source can I see that step?

But as @paoloricciuti says it might be as simple as doing something like this at 141

if (is_checkbox) {
    value = value || [];
    if (typeof value.includes === "function") input.checked = value.includes(input.__value);
    else if (typeof value.has === "function") input.checked = value.has(input.__value);
} else {
    input.checked = is(input.__value, value);
}