feat: enable snippets to fill slots #13427
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This allows people to use snippets to fill slots. It is implemented in the same way the default slot interop is already implemented, by passing a boolean to the hidden `$$slots` object, and using that at runtime to determine the correct outcome. The impact on bundle size is neglible. By enabling this, we can enhance our migration script to always transform slot usages (including `let:x` etc) to snippets. This wasn't possible before because we couldn't be sure if the other side was transformed to using render tags at the same time. This will be part of #13419. This is important because currently the migration script is transforming `<slot />` creations inside components, but since it's not touching its usage points the migration will make your app end up in a broken state which you have to finish by hand. This is a reduced alternative to, and closes #11619, which was also enabling the other way around, but that is a) not as necessary and b) more likely to confuse people / break, because it only works if your render function has 0-1 arguments.
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Hello, Just something that I think it's not correct. => I have a Svelte 4 component with a named slot, and it can be called using a slot or a snippet. => But when I migrate my component into Svelte 5, the call by => migrating a library component should not require everyone who uses it to change their code... |
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No that's what should happen IMO. If you're switching to the new syntax your users should, too. With the migration script this will be done for them, and if they don't want to yet they can stay on the old version of your component library |
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I don't think this is a good idea because it would add a big constraint : if a library is migrated to Svelte 5, all users of this library will be forced to migrate their own code... This will force to use the migration that can be difficult on large apps. I think it might even push library authors not to migrate their codes :
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Svelte 5 itself is backward compatible, but I don't think it's reasonable or desirable to expect libraries to be as well. This is a good change |
This allows people to use snippets to fill slots. It is implemented in the same way the default slot interop is already implemented, by passing a boolean to the hidden
$$slotsobject, and using that at runtime to determine the correct outcome. The impact on bundle size is neglible.By enabling this, we can enhance our migration script to always transform slot usages (including
let:xetc) to snippets. This wasn't possible before because we couldn't be sure if the other side was transformed to using render tags at the same time. This will be part of #13419. This is important because currently the migration script is transforming<slot />creations inside components, but since it's not touching its usage points the migration will make your app end up in a broken state which you have to finish by hand.This is a reduced alternative to, and closes #11619, which was also enabling the other way around, but that is a) not as necessary and b) more likely to confuse people / break, because it only works if your render function has 0-1 arguments.
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