Add support for Svelte 5 generics

[marekdedic]

Description

Hi,
generics are now officially part of Svelte 5. However, it seems to me that this parsers doesn't support them:

<script generics="KeyType extends number | string, ValueType" lang="ts">
  import type { Snippet } from "svelte";

  interface Props {
    children?: Snippet<[KeyType, ValueType]>;
    options: Array<[KeyType, ValueType]>;
    selected: Array<KeyType>;
  }

  let { children, options, selected = $bindable() }: Props = $props();

  selected;
</script>

{#each options as [id, value] (id)}
  <label>
    <input type="checkbox" value={id} bind:group={selected} />
    <span></span>
    {@render children?.(id, value)}
  </label>
{/each}

Gives 'ValueType' is not defined and similar

I tried to create a repro, but the playground is stuck at "Starting WebContainer"...

[ota-meshi]

I wasn't aware that generics were now an official feature 👀
For now it works fine if you enable it in the parser configuration.

See https://github.com/sveltejs/svelte-eslint-parser?tab=readme-ov-file#parseroptionssveltefeatures

      parserOptions: {
        // ...
        svelteFeatures: {
          experimentalGenerics: true,
        }
      },

[ota-meshi]

I tried to create a repro, but the playground is stuck at "Starting WebContainer"...

That link works fine on my local computer, I don't know what the problem is...

[marekdedic]

Great, I enabled the config and it works, thanks! They're official, so maybe it's time to stabilize them here as well :)

[ota-meshi]

Well, the RFC hasn't been merged yet, but it's in the official documentation so we can probably consider it an official feature.

They're official, so maybe it's time to stabilize them here as well :)

I think so 👍