Support svelte.config.ts

[tommywalkie]

This is a continuation of #1919 and most likely #2576, making use of Vite's loadConfigFromFile to handle TypeScript config file. For now this was only tested on a local SvelteKit project.

As mentionned in most threads, the remaining issue/quirk is making it work with other Svelte tools (like the VSCode plugin, which is expecting a svelte.config.js file).

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[changeset-bot]

🦋 Changeset detected

Latest commit: 90bdfda

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[dummdidumm]

I don't know how I feel about this. It feels wrong to support this half-way. There's not much value if you can use this in your build but your IDE/other tooling can't deal with it. This doesn't mean I'm not open to changing this on the tooling-side of things btw.

[tommywalkie]

@dummdidumm Yea pretty much. It does run the config file fine, then you inevitably find out the language server highlights your codebase in red. If anything, this could help in the future.

[benmccann]

the || 'production' shouldn't be needed because it is done here:

kit/packages/kit/src/cli.js

Line 91 in a8a3b14

process.env.NODE_ENV = process.env.NODE_ENV || 'production';

i'm worried that this might be putting it into production mode when you run svelte-kit dev

[tommywalkie]

Maybe this command needs a || 'production' (?)

kit/packages/kit/src/cli.js

Lines 147 to 153 in a8a3b14

	prog
	.command('package')
	.describe('Create a package')
	.option('-d, --dir', 'Destination directory', 'package')
	.action(async () => {
	try {
	const config = await load_config();

Otherwise, I considered using development as the default value for NODE_ENV.

[benmccann]

yeah, it seems reasonable to add a production default to the package command

[benmccann]

It seems somewhat reasonable to me. I'm not sure we should assume everyone uses VS Code. I'm a bit more split on whether we'd want to advertise it in the docs or not. Maybe we should caveat it there by saying the VS Code extension doesn't support it yet

[Rich-Harris]

I'm a strong 👎 on this. It adds moving parts to something that should be extremely simple and foolproof, and does so using an undocumented (and thus liable to change) API that's designed to load a Vite config, not a SvelteKit config (even if it happens to work today, is it guaranteed to work in future, despite whatever changes — to either Vite or Kit — we haven't anticipated?). As noted above, it will also cause problems with other tooling.

You can already type your config files (as shown throughout the docs). The use case presented in #2576 isn't something we should encourage in the first place (I didn't actually realise that we're promoting it in the FAQ; I should pay more attention to that page). The cost to benefit ratio is all wrong.

[bluwy]

-1 for me too. This wouldn't work for vite-plugin-svelte and I think it will be vital when we need to configure it in a SvelteKit project. I think we should wait for sveltejs/rfcs#59 first and slowly migrate the tooling towards it before making a new change.

[Rich-Harris]

I'm going to close this as the consensus seems to be that it's not a change we should make. Perhaps we can address it at an ecosystem level eventually per the mentioned RFC. Thanks