Allow `@const` inside `#key`

[michelAlexis]

Describe the problem

Hi !
After discussion on the discord, the question remains. Why isn't it possible to use @const inside #key ?

When @const is the first child of a #key, the compile gives us the "const_tag_invalid_placement". Which list every other # keywords, so why not #key ?

This is not a big deal. there are multiple workaround for that.

• <svelte:boundary> for inside loops when a parameter is necessary
• $derived but have to create an unused var

Small playground for reproduction and workarounds.

I don't know if this is just a missing feature/bug or if there are more implications that I am not aware of.

First time issue here, feel free to correct me I missed something, or close the issue if it's an intended behaviour.
I am not familiar enough to create a PR for this (As I don't know if editing the Visitor ConstTag is enough).

Describe the proposed solution

Allow @const inside #key as it make sense to create a template variable inside a reactive scope.

Importance

nice to have

[paoloricciuti]

I think it could make sense, and if you feel adventurous and want to try a PR the fix should be, like you said, to just add an extra condition in the const tag visitor. If you decide to so please make sure to also add a test in the validator folder with a key block with a const inside and an errors.json with an empty array in it.

Otherwise I'll see if I can open the PR myself later.

[michelAlexis]

Seems simple enough, I will give it a shot!
Just to be sure, this is the file you are talking about ? (A bit confused by the old and new test suite described in the readme)

[paoloricciuti]

Seems simple enough, I will give it a shot! Just to be sure, this is the file you are talking about ? (A bit confused by the old and new test suite described in the readme)

That's the folder...you need to create a new folder in the samples folder above that file with an unique name and an input.svelte file in it (or main.svelte I can never remember)...you can just take inspiration from the other folders

[Prinzhorn]

#8404