feat: allow adapter Vite plugins to be either pre or post - #16711
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teemingc
reviewed
Aug 10, 2026
… required, but the runtime treats them as optional, forcing adapter authors to always specify both.
This commit fixes the issue reported at packages/kit/src/exports/public.d.ts:75
## Bug
The new adapter `vite.plugins` option was typed with both sub-properties required:
```ts
vite?: {
plugins?: {
pre: Plugin[]; // required
post: Plugin[]; // required
};
};
```
However, the runtime in `packages/kit/src/exports/vite/index.js` (lines ~2059 and ~2070) consumes them with optional chaining and filters out falsy values:
```js
return /** @type {Plugin[]} */ (
[
svelte_config.kit.adapter?.vite?.plugins?.pre,
// ...SvelteKit's own plugins...
svelte_config.kit.adapter?.vite?.plugins?.post
].filter(Boolean)
);
```
Because of `?.` plus `.filter(Boolean)`, either `pre` or `post` being `undefined` is fully tolerated at runtime.
### Trigger
An adapter author who only wants to inject pre-plugins writes:
```ts
vite: { plugins: { pre: [myPlugin] } }
```
This is a valid, working configuration at runtime, but TypeScript reports an error because `post` is declared required (`Property 'post' is missing`). The author is forced to add `post: []` (and vice versa) purely to satisfy the types — an ergonomic regression from the previous `plugins?: Plugin[]` shape.
## Fix
Marked both `pre` and `post` as optional in the two generated/source type definitions so the types match the runtime's optional handling:
- `packages/kit/src/exports/public.d.ts`
- `packages/kit/types/index.d.ts`
```ts
plugins?: {
pre?: Plugin[];
post?: Plugin[];
};
```
The docs example (`documentation/docs/25-build-and-deploy/99-writing-adapters.md`) still shows both `pre: []` and `post: []`, which remains valid as an illustrative example now that each is individually optional.
Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com>
Co-authored-by: teemingc <chewteeming01@gmail.com>
Rich-Harris
pushed a commit
that referenced
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Aug 10, 2026
This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to version-3, this PR will be updated.⚠️ ⚠️ ⚠️ ⚠️ ⚠️ ⚠️ `version-3` is currently in **pre mode** so this branch has prereleases rather than normal releases. If you want to exit prereleases, run `changeset pre exit` on `version-3`.⚠️ ⚠️ ⚠️ ⚠️ ⚠️ ⚠️ # Releases ## @sveltejs/kit@3.0.0-next.18 ### Major Changes - breaking: separate adapter Vite plugins into `pre` and `post` ([#16711](#16711)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
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part of #16705
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