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Merged
teemingc merged 5 commits into from
Sep 1, 2026
Merged

feat: allow adapters to pass a function for vite config #16986

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32739ac
feat: allow adapters to pass a function for vite config
ottomated Aug 31, 2026
41a7ea4
remove generic
ottomated Sep 1, 2026
68a8a09
Update .changeset/fifty-breads-judge.md
ottomated Sep 1, 2026
f34ba6a
Merge branch 'version-3' into adapter-vite-function
ottomated Sep 1, 2026
0c1556e
remove cast
ottomated Sep 1, 2026
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6 changes: 6 additions & 0 deletions .changeset/fifty-breads-judge.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
"@sveltejs/kit": minor
---

feat: allow adapters to receive the Svelte config as a function argument when adding Vite plugins

20 changes: 9 additions & 11 deletions packages/adapter-cloudflare/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -203,17 +203,15 @@ export default function (options = {}) {
).cf = globalThis.__sveltekit_cloudflare_platform?.cf;
return request;
},
plugins: {
pre: [
virtual_workers_module(
{
configPath: options.config,
...options.platformProxy
},
stub_import
)
]
}
plugins: [
virtual_workers_module(
{
configPath: options.config,
...options.platformProxy
},
stub_import
)
]
}
};
}
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6 changes: 6 additions & 0 deletions packages/kit/src/core/config/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -200,6 +200,12 @@ export function validate_config(config) {
}
}

if (typeof config.adapter?.vite === 'function') {
validated.adapter.vite = config.adapter.vite({
config: validated
});
}

return validated;
} catch (e) {
const error = /** @type {Error} */ (e);
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69 changes: 41 additions & 28 deletions packages/kit/src/exports/public.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -57,34 +57,47 @@ export interface Adapter {
* during dev, build and prerendering.
*/
emulate?: () => MaybePromise<Emulator>;
vite?: {
/**
* This function overrides the default behavior during Vite's dev and preview modes
* to convert an `http.IncomingMessage` to a `Request` object.
* To call the original `setRequest` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
getRequest?: typeof getRequest;
/**
* This function overrides the default behavior in Vite's dev and preview modes
* to write a `Response` object to a `http.ServerResponse`.
* To call the original `setResponse` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
setResponse?: typeof setResponse;
plugins?: {
/**
* Vite plugins placed before any of SvelteKit's own plugins.
* @since 3.0.0
*/
pre?: Plugin[];
/**
* Vite plugins placed after any of SvelteKit's own plugins.
* @since 3.0.0
*/
post?: Plugin[];
};
};
/**
* Options for configuring and interacting with Vite
* @since 3.0.0
*/
vite?: AdapterViteConfig | ((ctx: { config: ValidatedConfig }) => AdapterViteConfig);
}

export interface AdapterViteConfig {
/**
* This function overrides the default behavior during Vite's dev and preview modes
* to convert an `http.IncomingMessage` to a `Request` object.
* To call the original `setRequest` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
getRequest?: typeof getRequest;
/**
* This function overrides the default behavior in Vite's dev and preview modes
* to write a `Response` object to a `http.ServerResponse`.
* To call the original `setResponse` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
setResponse?: typeof setResponse;
/**
* Vite plugins injected by the adapter. By default,
* they are placed before SvelteKit's plugins.
* @since 3.0.0
*/
plugins?:
| Plugin[]
| {
/**
* Vite plugins placed before any of SvelteKit's own plugins.
* @since 3.0.0
*/
pre?: Plugin[];
/**
* Vite plugins placed after any of SvelteKit's own plugins.
* @since 3.0.0
*/
post?: Plugin[];
};
Comment on lines +83 to +100

@teemingc teemingc Sep 1, 2026

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I feel a little conflicted about having the single array option default to pre. I kind of liked the explicitness of pre and post.

@ottomated ottomated Sep 1, 2026

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I think pre and post are only needed in very rare situations; it would be confusing to adapter authors if we required the specificity when it actually doesn't matter most of the time.

}

export type LoadProperties<input extends Record<string, any> | void> = input extends void
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6 changes: 6 additions & 0 deletions packages/kit/src/exports/vite/index.js
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Expand Up @@ -633,6 +633,12 @@ function kit({ svelte_config }) {
/** @type {(() => Promise<void>) | null} */
let finalise = null;

if (Array.isArray(svelte_config.adapter?.vite?.plugins)) {
svelte_config.adapter.vite.plugins = {
pre: svelte_config.adapter.vite.plugins
};
}

return /** @type {Plugin[]} */ (
[
svelte_config.adapter?.vite?.plugins?.pre,
Expand Down
7 changes: 5 additions & 2 deletions packages/kit/src/types/internal.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,9 @@ import {
Actions,
RequestEvent,
Emulator,
HttpError
HttpError,
Adapter,
AdapterViteConfig
} from '@sveltejs/kit';
import { RemoteFormIssue, RemoteQuery, RemoteLiveQuery } from '$app/server';
import { Config } from '@sveltejs/kit/vite';
Expand Down Expand Up @@ -592,7 +594,8 @@ export interface Uses {
search_params: Set<string>;
}

export type ValidatedConfig = RecursiveRequired<Omit<Config, 'preprocess'>> & {
export type ValidatedConfig = RecursiveRequired<Omit<Config, 'preprocess' | 'adapter'>> & {
adapter: Adapter & { vite?: AdapterViteConfig };
preprocess: Config['preprocess'];
};

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72 changes: 43 additions & 29 deletions packages/kit/types/index.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44,34 +44,47 @@ declare module '@sveltejs/kit' {
* during dev, build and prerendering.
*/
emulate?: () => MaybePromise<Emulator>;
vite?: {
/**
* This function overrides the default behavior during Vite's dev and preview modes
* to convert an `http.IncomingMessage` to a `Request` object.
* To call the original `setRequest` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
getRequest?: typeof getRequest;
/**
* This function overrides the default behavior in Vite's dev and preview modes
* to write a `Response` object to a `http.ServerResponse`.
* To call the original `setResponse` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
setResponse?: typeof setResponse;
plugins?: {
/**
* Vite plugins placed before any of SvelteKit's own plugins.
* @since 3.0.0
*/
pre?: Plugin[];
/**
* Vite plugins placed after any of SvelteKit's own plugins.
* @since 3.0.0
*/
post?: Plugin[];
};
};
/**
* Options for configuring and interacting with Vite
* @since 3.0.0
*/
vite?: AdapterViteConfig | ((ctx: { config: ValidatedConfig }) => AdapterViteConfig);
}

export interface AdapterViteConfig {
/**
* This function overrides the default behavior during Vite's dev and preview modes
* to convert an `http.IncomingMessage` to a `Request` object.
* To call the original `setRequest` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
getRequest?: typeof getRequest;
/**
* This function overrides the default behavior in Vite's dev and preview modes
* to write a `Response` object to a `http.ServerResponse`.
* To call the original `setResponse` function, import it from `@sveltejs/kit/node`.
* @since 3.0.0
*/
setResponse?: typeof setResponse;
/**
* Vite plugins injected by the adapter. By default,
* they are placed before SvelteKit's plugins.
* @since 3.0.0
*/
plugins?:
| Plugin[]
| {
/**
* Vite plugins placed before any of SvelteKit's own plugins.
* @since 3.0.0
*/
pre?: Plugin[];
/**
* Vite plugins placed after any of SvelteKit's own plugins.
* @since 3.0.0
*/
post?: Plugin[];
};
}

export type LoadProperties<input extends Record<string, any> | void> = input extends void
Expand Down Expand Up @@ -957,7 +970,8 @@ declare module '@sveltejs/kit' {
: T[K]; // Use the exact type for everything else
};

type ValidatedConfig = RecursiveRequired<Omit<Config, 'preprocess'>> & {
type ValidatedConfig = RecursiveRequired<Omit<Config, 'preprocess' | 'adapter'>> & {
adapter: Adapter & { vite?: AdapterViteConfig };
preprocess: Config['preprocess'];
};
/**
Expand Down
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