Array access not supported in the use or transition directives

[fcrozatier]

Describe the bug

This syntax

{#each assembly.speakers as speaker, i}
	<button use:assembly.speakers[i].action>speaker {i}</button>
{/each}

gets compiled down to

$.action(button, ($$node) => assembly["speakers[i]"].action($$node));

so the array access doesn't work.

But all the other variations do work so it's a bit confusing / seems like a bug.

Same thing for transitions

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAE5WS3W6DMAyFX8XLJg2kQu9bQNsz7LLpRUrdNRokKDarKsS7TwFCW3XazwWI-Dg-n206cdAVklhtOmFUjWIlXptGLASfG3-gT6wYxUKQbV3pIxmVTjdcSCNZ1411DN1B7bGHg7M1yOnKkp0ypFlbI8XaJ_unrBQRvDWoPtBBN4RZlT4LcohiyIsQlVxaQ7bCtLLvkRRHLUU8Sr0048fFA3LwEIPRJI9er0RY76ozhLo0mhPk8ESsGKPNNl5PnsO7dKgYA6THyosbKAaaRYOn0E8UhwqS-agpDVZp09Ixmk5xSHHIrTOh1KWzmX9wUoF_tArtRCNyUNMb5kHMlpdFmewhSWBvkcwzw8m6D5AmSQppukdU5XF2mZFBUSBbgB6wsl3LbA20hKu7_I3eptMetfleviyrCOPrdJ8tx7KeZelZ-sDrMelfhN3LNLPwQ_2AeXPh5j_6Bf5-FnPbf-9wmP20lv_3ee0-SVfDD5G_00CSFGIharvXB417sWLXYr_tvwCr6_BOHQQAAA==

Logs

No response

System Info

preview

Severity

annoyance

[Rich-Harris]

This isn't a bug, exactly, it's just a limitation of the syntax. Ultimately we don't want to invest more in actions (we have ideas for a better set of primitives) beyond matching what works in Svelte 4, so I'm going to close this — the recommended solution is to use the {@const ...} workaround.

[fcrozatier]

Ok makes sense. Just out of curiosity what would be the better primitives replacing actions?

[Rich-Harris]

Too soon to say exactly what they'd look like, but essentially we need a) better programmatic control over element lifecycle (to enable better coordination between different elements, to control when elements can be removed from the DOM, etc) and a syntax that doesn't force you to jump through hoops. It'll be a focus of a future release, post-5.0

[fcrozatier]

Sounds great. Hopefully this could be a spreadable syntax unlike use:, making it easier for libs to offer spreadable objects without worrying with overriding user actions unlike when spreading event attributes

[Rich-Harris]

Yep, making this stuff spreadable is very much part of the plan