feat: allow adapters to pass a function for vite config by ottomated · Pull Request #16986 · sveltejs/kit

ottomated · 2026-08-31T21:45:28Z

For adapter-cloudflare, we need to add @cloudflare/vite-plugin to the vite.plugins array. However, while configuring the plugin, we need access to svelte_config.out_dir in order to tell it how to generate the wrangler config.

This plugin allows adapters to do

  vite: ({ config }) => ({
    plugins: [
      some_plugin_that_requires(config),
    ]
  }

Drive-by, also allows adapters to just specify a plugins array if they don't need to specify pre and post. This is backwards-compatible.

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Summary by CodeRabbit

New Features
- Adapters can now configure Vite plugins dynamically using the validated SvelteKit configuration.
- Added support for defining adapter Vite plugins as an ordered list or separate pre/post groups.
- Expanded public adapter configuration types and documentation.
Bug Fixes
- Improved handling and ordering of adapter-provided Vite plugins.
Documentation
- Documented adapter Vite configuration options and plugin ordering.

pkg-svelte-dev · 2026-08-31T21:45:31Z

Install the latest version of @sveltejs/kit from 0c1556e:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/0c1556ea1e5fb00cff14e219af3f0bbdb84a02ee

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16986

changeset-bot · 2026-08-31T21:45:34Z

🦋 Changeset detected

Latest commit: 0c1556e

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	Minor

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svelte-docs-bot · 2026-08-31T21:48:22Z

Preview: https://svelte-dev-git-preview-kit-16986-svelte.vercel.app/

teemingc · 2026-09-01T16:41:53Z

+	 * 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[];
+		  };


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

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.

Co-authored-by: Tee Ming <chewteeming01@gmail.com>

coderabbitai · 2026-09-01T18:21:24Z

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Reviewing files that changed from the base of the PR and between 737984a and 0c1556e.

📒 Files selected for processing (7)

.changeset/fifty-breads-judge.md
packages/adapter-cloudflare/index.js
packages/kit/src/core/config/index.js
packages/kit/src/exports/public.d.ts
packages/kit/src/exports/vite/index.js
packages/kit/src/types/internal.d.ts
packages/kit/types/index.d.ts

🚧 Files skipped from review as they are similar to previous changes (7)

packages/kit/src/exports/vite/index.js
.changeset/fifty-breads-judge.md
packages/adapter-cloudflare/index.js
packages/kit/types/index.d.ts
packages/kit/src/core/config/index.js
packages/kit/src/exports/public.d.ts
packages/kit/src/types/internal.d.ts

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📝 Walkthrough

Walkthrough

SvelteKit now supports adapter Vite configuration callbacks that receive the validated configuration. Vite plugin arrays are normalized as pre plugins, and the Cloudflare adapter uses this format.

Changes

Adapter Vite configuration

Layer / File(s)	Summary
Adapter Vite configuration contract `packages/kit/src/exports/public.d.ts`, `packages/kit/types/index.d.ts`, `packages/kit/src/types/internal.d.ts`	`Adapter.vite` accepts static configuration or a callback receiving `ValidatedConfig`. The exported `AdapterViteConfig` interface defines request, response, and ordered plugin options.
Validated adapter configuration `packages/kit/src/core/config/index.js`	`validate_config` invokes `adapter.vite` callbacks with the validated configuration and stores the returned options.
Vite plugin normalization and adapter wiring `packages/kit/src/exports/vite/index.js`, `packages/adapter-cloudflare/index.js`, `.changeset/fifty-breads-judge.md`	Array-valued plugins are normalized into `pre` plugins. The Cloudflare adapter passes its virtual-workers plugin as an array. A minor release changeset documents the update.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 0c155

This PR adds the requested adapter configuration flexibility and remains merge-ready after normal checks and review; no actionable merge-blocking risk remains.

Sequence Diagram(s)

sequenceDiagram
  participant Adapter
  participant validate_config
  participant Vite
  participant PluginAssembly
  Adapter->>validate_config: provide adapter.vite callback
  validate_config->>Adapter: request validated configuration
  Adapter-->>validate_config: return AdapterViteConfig
  validate_config->>Vite: store resolved Vite configuration
  Vite->>PluginAssembly: normalize plugin array as pre plugins
  PluginAssembly-->>Vite: assemble ordered plugins

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: adapters can provide Vite configuration through a function.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 6 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 6 files. (1 skipped: 1 unsupported.)

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Commit unit tests in branch adapter-vite-function

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feat: allow adapters to pass a function for vite config

32739ac

teemingc added the adapters - general Support for functionality general to all adapters label Aug 31, 2026

teemingc reviewed Sep 1, 2026

View reviewed changes

ottomated and others added 3 commits September 1, 2026 10:18

remove generic

41a7ea4

Update .changeset/fifty-breads-judge.md

68a8a09

Co-authored-by: Tee Ming <chewteeming01@gmail.com>

Merge branch 'version-3' into adapter-vite-function

f34ba6a

teemingc approved these changes Sep 1, 2026

View reviewed changes

remove cast

0c1556e

teemingc merged commit 03f1687 into version-3 Sep 1, 2026
41 checks passed

teemingc deleted the adapter-vite-function branch September 1, 2026 19:04

github-actions Bot mentioned this pull request Sep 1, 2026

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

feat: allow adapters to pass a function for vite config#16986
teemingc merged 5 commits into
version-3from
adapter-vite-function

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