Svelte 5 TS: `class` property in template literal causes Unterminated template / Unexpected token!

[cshaa]

Describe the bug

Optional chaining to a property named class inside a template literal in a TypeScript script breaks the Svelte 5 parser.

Reproduction

<script lang="ts">
  const str = `${obj?.class}`;
</script>

Throws Unterminated template.

<script lang="ts">
  const str = `${obj?.class} ${42}`;
</script>

Throws Unexpected token.

Severity

blocking an upgrade

[GeoffCox]

+1 This happens for <script> tags as well. Maybe the compiler continues parsing for svelte within template strings.

<script>
	let example = `<script></script>`;
</script>

<pre>{example}</pre>

[MotionlessTrain]

+1 This happens for <script> tags as well. Maybe the compiler continues parsing for svelte within template strings.

<script>
	let example = `<script></script>`;
</script>

<pre>{example}</pre>

For script tags, this is to be expected (this breaks in exactly the same way in vanilla html)

The optional class property does look strange

[dummdidumm]

May be related to the acorn-typescript plugin we use to parse TS; without lang="ts" it works.

[elron]

I encounter this too

[plugin:vite-plugin-svelte] src/lib/components/UnicodeItem.svelte:4:9 Unexpected token
When I remove lang="ts" it works, but I need TS in some components so its blocking my upgrade.