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Add experimental Bun support #14817

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Merged
merged 11 commits into from
Oct 28, 2025
Merged

Add experimental Bun support #14817

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9dbd291
Support experimental Bun in Vercel Adapter
javivelasco Oct 27, 2025
c7923cb
Remove the experimental prefix in the actual output
javivelasco Oct 27, 2025
068f044
Rename experimental_bun to be just bun
javivelasco Oct 27, 2025
a8789f2
The default runtime should be bun if it is used for building
javivelasco Oct 27, 2025
edca606
Allow to opt-in with vercel.json to use bun
javivelasco Oct 27, 2025
eac096d
Fix experimental replacing
javivelasco Oct 27, 2025
da1e3e0
tweak
elliott-with-the-longest-name-on-github Oct 27, 2025
d722396
changeset
elliott-with-the-longest-name-on-github Oct 27, 2025
6b3be45
Update packages/adapter-vercel/index.js
elliott-with-the-longest-name-on-github Oct 27, 2025
6404bab
Update index.js
elliott-with-the-longest-name-on-github Oct 27, 2025
2b5ce56
Update index.js
elliott-with-the-longest-name-on-github Oct 27, 2025
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5 changes: 5 additions & 0 deletions .changeset/sour-fans-pay.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@sveltejs/adapter-vercel': minor
---

feat: Add experimental support for Bun runtime
3 changes: 1 addition & 2 deletions packages/adapter-vercel/index.d.ts
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Expand Up @@ -7,9 +7,8 @@ export interface ServerlessConfig {
/**
* Whether to use [Edge Functions](https://vercel.com/docs/concepts/functions/edge-functions) (`'edge'`) or [Serverless Functions](https://vercel.com/docs/concepts/functions/serverless-functions) (`'nodejs18.x'`, `'nodejs20.x'` etc).
* @default Same as the build environment
* @deprecated
*/
runtime?: `nodejs${number}.x`;
runtime?: `nodejs${number}.x` | `experimental_bun1.x`;
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@Rich-Harris Rich-Harris Oct 27, 2025

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maybe we should change this while we're at it, IIUC we only support 20 and 22. this will give better autocomplete as well as being more accurate

Suggested change
runtime?: `nodejs${number}.x` | `experimental_bun1.x`;
runtime?: `nodejs20.x` | `nodejs22.x` | `experimental_bun1.x`;

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@elliott-with-the-longest-name-on-github elliott-with-the-longest-name-on-github Oct 28, 2025

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Gonna make a followup PR for improving validation, I agree we can do better

/**
* To which regions to deploy the app. A list of regions.
* More info: https://vercel.com/docs/concepts/edge-network/regions
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21 changes: 15 additions & 6 deletions packages/adapter-vercel/index.js
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Expand Up @@ -294,7 +294,11 @@ const plugin = function (defaults = {}) {

// group routes by config
for (const route of builder.routes) {
const runtime = route.config?.runtime ?? defaults?.runtime ?? get_default_runtime();
const runtime = (
route.config?.runtime ??
defaults?.runtime ??
get_default_runtime()
).replace('experimental_', '');
const config = { runtime, ...defaults, ...route.config };

if (is_prerendered(route)) {
Expand All @@ -305,19 +309,24 @@ const plugin = function (defaults = {}) {
}

const node_runtime = /nodejs([0-9]+)\.x/.exec(runtime);
if (runtime !== 'edge' && (!node_runtime || parseInt(node_runtime[1]) < 20)) {
const bun_runtime = /^bun/.exec(runtime);
if (
runtime !== 'edge' &&
!bun_runtime &&
(!node_runtime || parseInt(node_runtime[1]) < 20)
) {
throw new Error(
`Invalid runtime '${runtime}' for route ${route.id}. Valid runtimes are 'edge' and 'nodejs20.x' or higher ` +
`Invalid runtime '${runtime}' for route ${route.id}. Valid runtimes are 'edge', 'experimental_bun1.x', 'nodejs20.x' or 'nodejs22.x' ` +
'(see the Node.js Version section in your Vercel project settings for info on the currently supported versions).'
);
}

if (config.isr) {
const directory = path.relative('.', builder.config.kit.files.routes + route.id);

if (!runtime.startsWith('nodejs')) {
if (!runtime.startsWith('nodejs') && !bun_runtime) {
throw new Error(
`${directory}: Routes using \`isr\` must use a Node.js runtime (for example 'nodejs20.x')`
`${directory}: Routes using \`isr\` must use a Node.js or Bun runtime (for example 'nodejs22.x' or 'experimental_bun1.x')`
);
}

Expand Down Expand Up @@ -400,7 +409,7 @@ const plugin = function (defaults = {}) {
// we need to create a catch-all route so that 404s are handled
// by SvelteKit rather than Vercel

const runtime = defaults.runtime ?? get_default_runtime();
const runtime = (defaults.runtime ?? get_default_runtime()).replace('experimental_', '');
const generate_function =
runtime === 'edge' ? generate_edge_function : generate_serverless_function;

Expand Down
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