[Svelte] Svelte 5 support

[ChqThomas]

Q	A
Bug fix?	no
New feature?	yes
Issues	/
License	MIT

Svelte 5 was just released 🚀

• Updated the peerDependencies of ux-svelte to support Svelte 5
• The controller has been adapted to continue supporting versions 3 and 4 of Svelte
• Some tests are only run on version 3/4, and some only on version 5
• Tested on a webpack-encore project successfuly
• Can't get it to work with an importmap (for asset-mapper) ATM, there is an opened issue on Svelte repo about this
• note : @sveltejs/vite-plugin-svelte updated to v3 only instead on v4 because v4 removed support for Svelte < 5

[smnandre]

Some reading here: https://svelte-5-preview.vercel.app/docs/breaking-changes

(just passing by)

[smnandre]

This will not work with AssetMapper right ? In which cas we need to find a solution because this would be a giant BC break :)

[ChqThomas]

That was my first thought but it worked when I tried it in ux.symfony.com !
I also tried to have import { mount } from 'svelte' at the top of the file but it doesn't work with AssetMapper with Svelte 4, an error was thrown because mount only exists in v5
I can't explain why but with a dynamic import there is no error, mount is just undefined

[smnandre]

I'll test this next week, thanks for the explanations :)

[ChqThomas]

Nice! FYI with AssetMapper it works with Svelte 4, but with Svelte 5 I'm stuck with the issue described here
I made a REPL with only html/js that reproduce the error

[smnandre]

Well that's pretty clear: https://svelte-omnisite.vercel.app/docs/svelte/v5-migration-guide

[Kocal]

I'm starting to investigate what's missing to make Svelte 5 happy here, just personal notes:

• svelte 4.x sf console importmap:require svelte@4.2.19 svelte/internal@4.2.19 svelte/internal/disclose-version@4.2.19 && pnpm add -D svelte@4.2.19 && pnpm run build-svelte
• svelte 5.x sf console importmap:require svelte svelte/internal/client svelte/internal/disclose-version && pnpm add -D svelte && pnpm run build-svelte@5.1.6
• svelte version and packages in importmap definition will need to be updated

[ChqThomas]

I'm starting to investigate what's missing to make Svelte 5 happy here, just personal notes:

• svelte 4.x sf console importmap:require svelte@4.2.19 svelte/internal@4.2.19 svelte/internal/disclose-version@4.2.19 && pnpm add -D svelte@4.2.19 && pnpm run build-svelte
• svelte 5.x sf console importmap:require svelte svelte/internal/client svelte/internal/disclose-version && pnpm add -D svelte && pnpm run build-svelte@5.1.6
• svelte version and packages in importmap definition will need to be updated

Small tips: you can get rid of the svelte/internal/disclose-version dependency if you compile the Svelte components with the discloseVersion: false option - documentation

[Kocal]

Ok I think I'm on something. I believe that's because the context between svelte and svelte/internal/client is not shared.

In one of the module, init_operations() is called and first_child_getter and next_sibling_getter are defined.
But, on the other module, which depends of first_child_getter and next_sibling_getter, calls to get_first_child (called by mount) fails because first_child_getter is undefined.

I believe this is related to no-build scenarios, like we do with AssetMapper/importmap.

I will investigate more and try to find a solution.

[smnandre]

I believe this is related to no-build scenarios, like we do with AssetMapper/importmap.

I will investigate more and try to find a solution.

It is, and some people are trying weird stuff with chunks (i'm not sure to even understand what i'm saying here haha)

[Kocal]

To be honest, due to how files are bundled on JSDelivr and how Svelte 5 works, I don't know if we can have Svelte 5 support for AssetMapper... :/

[smnandre]

I'd be ok if the support was only for webpack :| But no BC break for AssetMapper please :)

But i don't get how this work as... in the end... there are only compiled assets in a directory right ?

[Kocal]

But i don't get how this work as... in the end... there are only compiled assets in a directory right ?

Not with AssetMapper / CDN stuff.

When you compile this .svelte file for Svelte 5:

<script>
    export let name = "Svelte";
</script>

<div>Hello {name}</div>

It become:

import * as $ from "svelte/internal/client";

var root = $.template(`<div> </div>`);

export default function _unknown_($$anchor, $$props) {
	let name = $.prop($$props, "name", 8, "Svelte");
	var div = root();
	var text = $.child(div);

	$.reset(div);
	$.template_effect(() => $.set_text(text, `Hello ${name() ?? ""}`));
	$.append($$anchor, div);
}

Here, we have a dependency to svelte/internal/client, you can install it through importmap:require.

In the render_controller.ts file, we have a dependency to svelte to import mount and unmount functions (if they exists, in Svelte 5). You can also install svelte through importmap:require.

The thing is, that both dependencies svelte and svelte/internal/client contain both the same inlined (and that's the problem) logic (the function init_operations() instead of relying on a common module.

One dependency defines first_child_getter and next_sibling_getter function, and the other dependency tries to use those functions but without success, since the context is not shared across the two dependencies... :/

IMO, the best we can do is to:

1. keep render_controller.js as-if, only support Svelte 3/4
2. and either:
   1. since we can do BC breaks here, create a new UX package symfony/ux-svelte-5, without AssetMapper support, with good devDependencies versions, that's the easier and cleanest solution
   2. or a more and more complex solution with some drawbacks :
      1. add a new option svelte.comptability_version (default to 4),
      2. create a new Stimulus controller for Svelte 5,
      3. try to see how can we warn the user that nothing will work if you use the AssetMapper with svelte.comptability_version = 5, but I don't know how we can do that properly
      4. but, the importmap.php and package.json dependencies will be invalid because by default they contains deps for Svelte 3/4 :/

I'm more in favor of a new dedicated symfony/ux-svelte-5 package, as it will be more easier for us to work on, and more easier for users to use it.

[ChqThomas]

The potential issue I see with creating a new ux-svelte-5 package now is that if Svelte fixes the CDN issue in a future release, we'll have to do a BC break to remove the new package and come back to the initial one

[smnandre]

There is not much code in the package, i'm sure we can make something in it to load or or the other file :)

[Kocal]

There is not much code in the package, i'm sure we can make something in it to load or or the other file :)

Yeah, but for the moment Svelte 5 only works with Webpack, not with AssetMapper. Even if we can do something "to load or not the other file", it still won't work :s or am I missing something?

[smnandre]

Yeah, but for the moment Svelte 5 only works with Webpack, not with AssetMapper.

That's what i reacted on when i said "i'd be ok to no have AssetMapper support"

We can announce a compatibility for only Webpack no ?

[Kocal]

Yes we can