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Svelte 5: @const treats multiple declarations as sequence expression #11349

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jrmajor opened this issue Apr 27, 2024 · 2 comments · Fixed by #11357
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Svelte 5: @const treats multiple declarations as sequence expression #11349

jrmajor opened this issue Apr 27, 2024 · 2 comments · Fixed by #11357
Milestone
5.0

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@jrmajor
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jrmajor commented Apr 27, 2024 •
edited

Describe the bug

{#if true}
	{@const foo = 'foo', bar = 'bar'}
{/if}

The following code fails to compile in Svelte 4 ({@const ...} must be an assignment.).

In Svelte 5, it treats 'foo', bar = 'bar' as a sequence expression, which is not how const declarations work in JS.

const foo = 'foo', bar = 'bar';
console.log(foo); // 'foo'
console.log(bar); // 'bar'

Reproduction

REPL: Svelte 4 / Svelte 5

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No response

System Info

Only tested in REPL.

Severity

annoyance
@Infectious-Smile

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@dummdidumm
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It should be a compiler error in Svelte 5

@dummdidumm dummdidumm added this to the 5.0 milestone Apr 27, 2024
dummdidumm added a commit that referenced this issue Apr 28, 2024
@dummdidumm
fix: disallow sequence expressions in @const tags
bbde079 
closes #11349
@dummdidumm dummdidumm mentioned this issue Apr 28, 2024
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Rich-Harris pushed a commit that referenced this issue Apr 29, 2024
@dummdidumm
fix: disallow sequence expressions in @const tags (#11357)
5e0845f 
* fix: disallow sequence expressions in `@const` tags

closes #11349

* allow parenthesized sequence expression
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fix: disallow sequence expressions in @const tags sveltejs/svelte
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@dummdidumm @jrmajor @Infectious-Smile