Generate type declarations with dts-buddy

[Rich-Harris]

This provides us with better type declarations and a smaller package. On the version-4 branch, the types directory takes 300kb (or 1.1MB on disk, because it's 264 separate files). In this PR, it takes 23kb (25kb on disk) with two files.

All the types are put into a single bundle, and treeshaken (so we don't ship internal types that aren't referenced by public APIs).

As well as the size benefits, this provides a much better experience for Svelte users. This is what happens today:

dts-buddy-before.mov

Notice a few things:

• VSCode auto-imports svelte/internal.js. svelte is available in the auto-import menu (it's confusing that they're both there), but you have to actively select it
• Cmd-clicking on onMount takes you to the .d.ts file, rather than the implementation. (Even though the implementation isn't all that self-explanatory in the case of onMount, developers overwhelmingly prefer this behaviour.)
• Typing in:fade doesn't trigger an auto-import for svelte/transition — VSCode simply can't find it. It can find a horrendous list of internal junk like fix_and_destroy_block from svelte/types/runtime/internal/each
• When you manually import it, it tries to autocomplete to svelte/transition.js, most likely because of my editor configuration. This will not resolve correctly
• you can cmd-click on fade but, again, it takes you to the type declaration. This time, it is useful to go straight to the implementation, to understand how you'd build your own custom transition

With this PR, things look very different:

dts-buddy-after.mov

Because it uses declare module, nothing relies on the app developer having the right TypeScript/editor configuration (moduleResolution, file extension preferences etc) to get the right imports, and there are no false positives — just the public API.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
svelte-dev-2	❌ Failed (Inspect)			Jun 8, 2023 0:54am

[benmccann]

cool!!

btw, one thing I noticed is that if you build twice on the sites branch then the types generation fails. might be worth taking a look at while you're in this section of the code

[PuruVJ]

That's cuz the sites' script expects multiple files it can bundle using roll-up plugin dts. This PR renders the entire logic useless. We'll need to rewrite the script to account for the declare module stuff now, although it should be faaaar more easier now

[Rich-Harris]

ah yeah, that makes sense — had to make a similar change on the kit repo https://github.com/sveltejs/kit/pull/9992/files#diff-a139886ac75fed1841162f1a5ba8fdfa4fca12f24428f065a9f978e41840ba82

[dummdidumm]

There's one thing I'd like to add back (manually?) somehow or at least make aware of which is the svelte/types/preprocess import that many other packages rely on (including svelte-preprocess and SvelteKit) because for some reason we never publicly exposed the preprocessor types. Removing that type path might be a bit too breaking for v4

[benmccann]

There's one thing I'd like to add back (manually?) somehow or at least make aware of which is the svelte/types/preprocess import that many other packages rely on (including svelte-preprocess and SvelteKit) because for some reason we never publicly exposed the preprocessor types. Removing that type path might be a bit too breaking for v4

To clarify, it looks like it's actually svelte/types/compiler/preprocess and it's svelte-preprocess and vite-plugin-svelte that depend on it.

[Rich-Harris]

Those types should probably be part of the svelte/compiler module (which I forgot to add to this PR anyway). Perhaps we add them there, and re-export them from svelte/types/compiler/preprocess but also deprecate them, so that in v5 we can safely drop them altogether?

[Rich-Harris]

Ok, I've added svelte/compiler and svelte/types/compiler/preprocess. I propose that we cut major releases of svelte-preprocess and vite-plugin-svelte during 4.x that switch over to importing the relevant types from svelte/compiler, and then we can remove svelte/types/compiler/preprocess in 5.0

I think this PR is probably ready to go, unless there's anything else you can see?

[gtm-nayan]

I propose that we cut major releases of svelte-preprocess and vite-plugin-svelte during 4.x that switch over to importing the relevant types from svelte/compiler

Do those have to be majors?

[gtm-nayan]

Lint is failing btw

[PuruVJ]

Some folks do use svelte/internal. Does this change mean they won't get any typing from that?

[PuruVJ]

Many types are missing as well. Is this fine for final usage or something is broken?

[Rich-Harris]

Do those have to be majors?

Yeah, because they'd need to drop support for Svelte 3

[Rich-Harris]

Some folks do use svelte/internal. Does this change mean they won't get any typing from that?

They shouldn't be! And yes, they'll lose typing (in fact I think using those things will cause typechecking to fail, which is good)

Many types are missing

Dammit I broke something in dts-buddy. Investigating

[dominikg]

v-p-s is likely going to do a major for vite5 / drop node16 in September or early October

[Rich-Harris]

Many types are missing

Should be fixed now

[Rich-Harris]

this has a decent effect on package size:

[PuruVJ]

learn.svelte.dev also will boot up so much faster now!!! 🔥 Does this release include the dequel change in ARIAQuery yet?

[benmccann]

Does this release include the dequel change in ARIAQuery yet?

No. That change has been merged, but not released. They said hopefully later this week they can cut a release

[PuruVJ]

Damn!! So it can down even more 🔥