refactor(vercel): support bun runtime (#3678)

Author: QuiiBz

docs/2.deploy/20.providers/vercel.md

@@ -44,6 +44,31 @@ export default defineNuxtConfig({
 
 Framework integrations can use the `ssrRoutes` configuration to declare SSR routes. For more information, see [#3475](https://github.com/nitrojs/nitro/pull/3475).
 
+## Bun runtime
+
+:read-more{title="Vercel" to="https://vercel.com/docs/functions/runtimes/bun"}
+
+You can use [Bun](https://bun.com) instead of Node.js by specifying the runtime using the `vercel.functions` key inside `nitro.config`:
+
+```ts [nitro.config.ts]
+export default defineNitroConfig({
+  vercel: {
+    functions: {
+      runtime: "bun1.x"
+    }
+  }
+})
+```
+
+<!-- Alternatively, Nitro also detects Bun automatically if you specify a `bunVersion` property in your `vercel.json`:
+
+```json [vercel.json]
+{
+  "$schema": "https://openapi.vercel.sh/vercel.json",
+  "bunVersion": "1.x"
+}
+``` -->
+
 ## Custom build output configuration
 
 You can provide additional [build output configuration](https://vercel.com/docs/build-output-api/v3) using `vercel.config` key inside `nitro.config`. It will be merged with built-in auto-generated config.

src/presets/vercel/types.ts

@@ -101,6 +101,11 @@ export interface VercelServerlessFunctionConfig {
    */
   shouldAddSourcemapSupport?: boolean;
 
+  /**
+   * The runtime to use. Defaults to the auto-detected Node.js version.
+   */
+  runtime?: "nodejs20.x" | "nodejs22.x" | "bun1.x" | (string & {});
+
   [key: string]: unknown;
 }
 

src/presets/vercel/utils.ts

@@ -38,23 +38,38 @@ export async function generateFunctionFiles(nitro: Nitro) {
   const buildConfig = generateBuildConfig(nitro, o11Routes);
   await writeFile(buildConfigPath, JSON.stringify(buildConfig, null, 2));
 
-  const systemNodeVersion = getSystemNodeVersion();
-  const usedNodeVersion =
-    SUPPORTED_NODE_VERSIONS.find((version) => version >= systemNodeVersion) ??
-    SUPPORTED_NODE_VERSIONS.at(-1);
+  // Runtime
+  // 1. Respect explicit runtime from nitro config
+  let runtime: VercelServerlessFunctionConfig["runtime"] =
+    nitro.options.vercel?.functions?.runtime;
+  // 2. Read runtime from vercel.json if specified
+  if (!runtime) {
+    const vercelConfig = await readVercelConfig(nitro.options.rootDir);
+    // Use bun runtime if bunVersion is specified or bun used to build
+    if (vercelConfig.bunVersion || "Bun" in globalThis) {
+      runtime = `bun${vercelConfig.bunVersion || "1.x"}`;
+    } else {
+      // 3. Auto-detect runtime based on system Node.js version
+      const systemNodeVersion = getSystemNodeVersion();
+      const usedNodeVersion =
+        SUPPORTED_NODE_VERSIONS.find(
+          (version) => version >= systemNodeVersion
+        ) ?? SUPPORTED_NODE_VERSIONS.at(-1);
+      runtime = `nodejs${usedNodeVersion}.x`;
+    }
+  }
 
-  const runtimeVersion = `nodejs${usedNodeVersion}.x`;
   const functionConfigPath = resolve(
     nitro.options.output.serverDir,
     ".vc-config.json"
   );
   const functionConfig: VercelServerlessFunctionConfig = {
-    runtime: runtimeVersion,
+    runtime,
+    ...nitro.options.vercel?.functions,
     handler: "index.mjs",
     launcherType: "Nodejs",
     shouldAddHelpers: false,
     supportsResponseStreaming: true,
-    ...nitro.options.vercel?.functions,
   };
   await writeFile(functionConfigPath, JSON.stringify(functionConfig, null, 2));
 
@@ -273,6 +288,23 @@ export function deprecateSWR(nitro: Nitro) {
   }
 }
 
+// --- vercel.json ---
+
+// https://vercel.com/docs/project-configuration
+// https://openapi.vercel.sh/vercel.json
+export interface VercelConfig {
+  bunVersion?: string;
+}
+
+export async function readVercelConfig(rootDir: string): Promise<VercelConfig> {
+  const vercelConfigPath = resolve(rootDir, "vercel.json");
+  const vercelConfig = await fsp
+    .readFile(vercelConfigPath)
+    .then((config) => JSON.parse(config.toString()))
+    .catch(() => ({}));
+  return vercelConfig as VercelConfig;
+}
+
 function _hasProp(obj: any, prop: string) {
   return obj && typeof obj === "object" && prop in obj;
 }

test/presets/vercel.test.ts

@@ -1,8 +1,7 @@
 import { promises as fsp } from "node:fs";
-import { resolve, join, relative, basename } from "pathe";
-import { describe, expect, it } from "vitest";
-import { setupTest, startServer, testNitro } from "../tests";
-import { readlink } from "node:fs/promises";
+import { resolve, join, basename } from "pathe";
+import { describe, expect, it, afterAll } from "vitest";
+import { setupTest, startServer, testNitro, fixtureDir } from "../tests";
 
 describe("nitro:preset:vercel", async () => {
   const ctx = await setupTest("vercel");
@@ -591,3 +590,68 @@ describe("nitro:preset:vercel", async () => {
     }
   );
 });
+
+describe("nitro:preset:vercel:bun", async () => {
+  const ctx = await setupTest("vercel", {
+    config: {
+      preset: "vercel",
+      vercel: {
+        functions: {
+          runtime: "bun1.x",
+        },
+      },
+    },
+  });
+
+  it("should generate function config with bun runtime", async () => {
+    const config = await fsp
+      .readFile(
+        resolve(ctx.outDir, "functions/__fallback.func/.vc-config.json"),
+        "utf8"
+      )
+      .then((r) => JSON.parse(r));
+    expect(config).toMatchInlineSnapshot(`
+      {
+        "handler": "index.mjs",
+        "launcherType": "Nodejs",
+        "runtime": "bun1.x",
+        "shouldAddHelpers": false,
+        "supportsResponseStreaming": true,
+      }
+    `);
+  });
+});
+
+describe("nitro:preset:vercel:bun-verceljson", async () => {
+  const vercelJsonPath = join(fixtureDir, "vercel.json");
+  // Need to make sure vercel.json is created before setupTest is called
+  await fsp.writeFile(vercelJsonPath, JSON.stringify({ bunVersion: "1.x" }));
+
+  const ctx = await setupTest("vercel", {
+    config: {
+      preset: "vercel",
+    },
+  });
+
+  afterAll(async () => {
+    await fsp.unlink(vercelJsonPath).catch(() => {});
+  });
+
+  it("should detect bun runtime from vercel.json", async () => {
+    const config = await fsp
+      .readFile(
+        resolve(ctx.outDir, "functions/__fallback.func/.vc-config.json"),
+        "utf8"
+      )
+      .then((r) => JSON.parse(r));
+    expect(config).toMatchInlineSnapshot(`
+      {
+        "handler": "index.mjs",
+        "launcherType": "Nodejs",
+        "runtime": "bun1.x",
+        "shouldAddHelpers": false,
+        "supportsResponseStreaming": true,
+      }
+    `);
+  });
+});