[static-build] Support subset of Build Output API v2 (#7808)

* Revert "Revert "[static-build] Support subset of Build Output API v2" (#7803)"

This reverts commit dfb6ef949b.

* more specific v2 detection

* use nuxt@3.0.0-rc.3 to make sure the incident is resolved

* set test timeout to see if this works in CI

* update CI node version to 14

* add node_modules because it was taking too long to install in CI

* remove timeout

* remove node modules

* remove the nuxt@3 dependency

* finish update to node 14

* blank yarn.lock

* revert node version update

* fix revert

* remove newline

examples/solidstart/.gitignore

@@ -2,6 +2,7 @@ dist
 worker
 .solid
 .vercel
+.output
 
 # dependencies
 /node_modules

packages/static-build/package.json

@@ -32,6 +32,7 @@
   "devDependencies": {
     "@types/aws-lambda": "8.10.64",
     "@types/cross-spawn": "6.0.0",
+    "@types/fs-extra": "9.0.13",
     "@types/jest": "27.4.1",
     "@types/ms": "0.7.31",
     "@types/node-fetch": "2.5.4",

packages/static-build/src/index.ts

@@ -32,6 +32,7 @@ import {
 } from '@vercel/build-utils';
 import type { Route, Source } from '@vercel/routing-utils';
 import * as BuildOutputV1 from './utils/build-output-v1';
+import * as BuildOutputV2 from './utils/build-output-v2';
 import * as BuildOutputV3 from './utils/build-output-v3';
 import * as GatsbyUtils from './utils/gatsby';
 import * as NuxtUtils from './utils/nuxt';
@@ -261,6 +262,37 @@ async function fetchBinary(url: string, framework: string, version: string) {
   });
 }
 
+async function getUpdatedDistPath(
+  framework: Framework | undefined,
+  outputDirPrefix: string,
+  entrypointDir: string,
+  distPath: string,
+  config: Config
+): Promise<string | undefined> {
+  if (framework) {
+    const outputDirName = config.outputDirectory
+      ? config.outputDirectory
+      : await framework.getOutputDirName(outputDirPrefix);
+
+    return path.join(outputDirPrefix, outputDirName);
+  }
+
+  if (!config || !config.distDir) {
+    // Select either `dist` or `public` as directory
+    const publicPath = path.join(entrypointDir, 'public');
+
+    if (
+      !existsSync(distPath) &&
+      existsSync(publicPath) &&
+      statSync(publicPath).isDirectory()
+    ) {
+      return publicPath;
+    }
+  }
+
+  return undefined;
+}
+
 export const build: BuildV2 = async ({
   files,
   entrypoint,
@@ -629,48 +661,36 @@ export const build: BuildV2 = async ({
       }
 
       const outputDirPrefix = path.join(workPath, path.dirname(entrypoint));
+      distPath =
+        (await getUpdatedDistPath(
+          framework,
+          outputDirPrefix,
+          entrypointDir,
+          distPath,
+          config
+        )) || distPath;
 
       // If the Build Command or Framework output files according to the
       // Build Output v3 API, then stop processing here in `static-build`
       // since the output is already in its final form.
-      const buildOutputPath = await BuildOutputV3.getBuildOutputDirectory(
+      const buildOutputPathV3 = await BuildOutputV3.getBuildOutputDirectory(
         outputDirPrefix
       );
-
-      if (buildOutputPath) {
+      if (buildOutputPathV3) {
         // Ensure that `vercel build` is being used for this Deployment
-        if (!meta.cliVersion) {
-          let buildCommandName: string;
-          if (buildCommand) buildCommandName = `"${buildCommand}"`;
-          else if (framework) buildCommandName = framework.name;
-          else buildCommandName = 'the "build" script';
-          throw new Error(
-            `Detected Build Output v3 from ${buildCommandName}, but this Deployment is not using \`vercel build\`.\nPlease set the \`ENABLE_VC_BUILD=1\` environment variable.`
-          );
-        }
-        return {
-          buildOutputVersion: 3,
-          buildOutputPath,
-        };
+        return BuildOutputV3.createBuildOutput(
+          meta,
+          buildCommand,
+          buildOutputPathV3,
+          framework
+        );
       }
 
-      if (framework) {
-        const outputDirName = config.outputDirectory
-          ? config.outputDirectory
-          : await framework.getOutputDirName(outputDirPrefix);
-
-        distPath = path.join(outputDirPrefix, outputDirName);
-      } else if (!config || !config.distDir) {
-        // Select either `dist` or `public` as directory
-        const publicPath = path.join(entrypointDir, 'public');
-
-        if (
-          !existsSync(distPath) &&
-          existsSync(publicPath) &&
-          statSync(publicPath).isDirectory()
-        ) {
-          distPath = publicPath;
-        }
+      const buildOutputPathV2 = await BuildOutputV2.getBuildOutputDirectory(
+        outputDirPrefix
+      );
+      if (buildOutputPathV2) {
+        return await BuildOutputV2.createBuildOutput(workPath);
       }
 
       const extraOutputs = await BuildOutputV1.readBuildOutputDirectory({

packages/static-build/src/utils/build-output-v2.ts

@@ -0,0 +1,184 @@
+import path from 'path';
+import { pathExists, readJson, appendFile } from 'fs-extra';
+import { Route } from '@vercel/routing-utils';
+import {
+  Files,
+  FileFsRef,
+  debug,
+  glob,
+  EdgeFunction,
+  BuildResultV2,
+} from '@vercel/build-utils';
+import { isObjectEmpty } from './_shared';
+
+const BUILD_OUTPUT_DIR = '.output';
+const BRIDGE_MIDDLEWARE_V2_TO_V3 = `
+
+
+// appended to convert v2 middleware to v3 middleware
+export default async (request) => {
+  const { response } = await _ENTRIES['middleware_pages/_middleware'].default({ request });
+  return response;
+}
+`;
+
+const CONFIG_FILES = [
+  'build-manifest.json',
+  'functions-manifest.json',
+  'images-manifest.json',
+  'prerender-manifest.json',
+  'routes-manifest.json',
+];
+
+/**
+ * Returns the path to the Build Output API v2 directory when any
+ * relevant config file was created by the framework / build script,
+ * or `undefined` if the framework did not create the v2 output.
+ */
+export async function getBuildOutputDirectory(
+  workingDir: string
+): Promise<string | undefined> {
+  const outputDir = path.join(workingDir, BUILD_OUTPUT_DIR);
+
+  // check for one of several config files
+  const finderPromises = CONFIG_FILES.map(configFile => {
+    return pathExists(path.join(outputDir, configFile));
+  });
+
+  const finders = await Promise.all(finderPromises);
+  if (finders.some(found => found)) {
+    return outputDir;
+  }
+  return undefined;
+}
+
+/**
+ * Reads the BUILD_OUTPUT_DIR directory and returns and object
+ * that should be merged with the build outputs.
+ */
+export async function readBuildOutputDirectory({
+  workPath,
+}: {
+  workPath: string;
+}) {
+  // Functions are not supported, but are used to support Middleware
+  const functions: Record<string, EdgeFunction> = {};
+
+  // Routes are not supported, but are used to support Middleware
+  const routes: Array<Route> = [];
+
+  const middleware = await getMiddleware(workPath);
+  if (middleware) {
+    routes.push(middleware.route);
+
+    functions['middleware'] = new EdgeFunction({
+      deploymentTarget: 'v8-worker',
+      entrypoint: '_middleware.js',
+      files: {
+        '_middleware.js': middleware.file,
+      },
+      name: 'middleware',
+    });
+  }
+
+  const staticFiles = await readStaticFiles({ workPath });
+
+  const outputs = {
+    staticFiles: isObjectEmpty(staticFiles) ? null : staticFiles,
+    functions: isObjectEmpty(functions) ? null : functions,
+    routes: routes.length ? routes : null,
+  };
+
+  if (outputs.functions) {
+    debug(`Detected Serverless Functions in "${BUILD_OUTPUT_DIR}"`);
+  }
+
+  if (outputs.staticFiles) {
+    debug(`Detected Static Assets in "${BUILD_OUTPUT_DIR}"`);
+  }
+
+  if (outputs.routes) {
+    debug(`Detected Routes Configuration in "${BUILD_OUTPUT_DIR}"`);
+  }
+
+  return outputs;
+}
+
+async function getMiddleware(
+  workPath: string
+): Promise<{ route: Route; file: FileFsRef } | undefined> {
+  const manifestPath = path.join(
+    workPath,
+    BUILD_OUTPUT_DIR,
+    'functions-manifest.json'
+  );
+
+  try {
+    const manifest = await readJson(manifestPath);
+    if (manifest.pages['_middleware.js'].runtime !== 'web') {
+      return;
+    }
+  } catch (error) {
+    if (error.code !== 'ENOENT') throw error;
+    return;
+  }
+
+  const middlewareRelativePath = path.join(
+    BUILD_OUTPUT_DIR,
+    'server/pages/_middleware.js'
+  );
+
+  const middlewareAbsoluatePath = path.join(workPath, middlewareRelativePath);
+  await appendFile(middlewareAbsoluatePath, BRIDGE_MIDDLEWARE_V2_TO_V3);
+
+  const route = {
+    src: '/(.*)',
+    middlewarePath: 'middleware',
+    continue: true,
+  };
+
+  return {
+    route,
+    file: new FileFsRef({
+      fsPath: middlewareRelativePath,
+    }),
+  };
+}
+
+async function readStaticFiles({
+  workPath,
+}: {
+  workPath: string;
+}): Promise<Files> {
+  const staticFilePath = path.join(workPath, BUILD_OUTPUT_DIR, 'static');
+  const staticFiles = await glob('**', {
+    cwd: staticFilePath,
+  });
+
+  return staticFiles;
+}
+
+export async function createBuildOutput(
+  workPath: string
+): Promise<BuildResultV2> {
+  let output: Files = {};
+  const routes: Route[] = [];
+
+  const extraOutputs = await readBuildOutputDirectory({
+    workPath,
+  });
+
+  if (extraOutputs.routes) {
+    routes.push(...extraOutputs.routes);
+  }
+
+  if (extraOutputs.staticFiles) {
+    output = Object.assign(
+      {},
+      extraOutputs.staticFiles,
+      extraOutputs.functions
+    );
+  }
+
+  return { routes, output };
+}

packages/static-build/src/utils/build-output-v3.ts

@@ -1,10 +1,12 @@
 import { join } from 'path';
 import { promises as fs } from 'fs';
+import { BuildResultV2, Meta } from '../../../build-utils/dist';
+import { Framework } from '../../../frameworks/dist/types';
 
 const BUILD_OUTPUT_DIR = '.vercel/output';
 
 /**
- * Returns the path to the Build Output v3 directory when the
+ * Returns the path to the Build Output API v3 directory when the
  * `config.json` file was created by the framework / build script,
  * or `undefined` if the framework did not create the v3 output.
  */
@@ -34,3 +36,27 @@ export async function readConfig(
   }
   return undefined;
 }
+
+export function createBuildOutput(
+  meta: Meta,
+  buildCommand: string | null,
+  buildOutputPath: string,
+  framework?: Framework
+): BuildResultV2 {
+  if (!meta.cliVersion) {
+    let buildCommandName: string;
+
+    if (buildCommand) buildCommandName = `"${buildCommand}"`;
+    else if (framework) buildCommandName = framework.name;
+    else buildCommandName = 'the "build" script';
+
+    throw new Error(
+      `Detected Build Output v3 from ${buildCommandName}, but this Deployment is not using \`vercel build\`.\nPlease set the \`ENABLE_VC_BUILD=1\` environment variable.`
+    );
+  }
+
+  return {
+    buildOutputVersion: 3,
+    buildOutputPath,
+  };
+}

packages/static-build/test/build-fixtures/09-build-output-v3/.gitignore

@@ -0,0 +1 @@
+yarn.lock

packages/static-build/test/build-fixtures/09-build-output-v3/build.js

@@ -3,5 +3,5 @@ fs.mkdirSync('.vercel/output/static', { recursive: true });
 fs.writeFileSync('.vercel/output/config.json', '{}');
 fs.writeFileSync(
   '.vercel/output/static/index.html',
-  '<h1>Build Output API</h1>'
+  '<h1>Build Output API v3</h1>'
 );

packages/static-build/test/build-fixtures/10-build-output-v2/.gitignore

@@ -0,0 +1 @@
+yarn.lock

packages/static-build/test/build-fixtures/10-build-output-v2/build.js

@@ -0,0 +1,60 @@
+const fs = require('fs');
+
+fs.mkdirSync('.output/static', { recursive: true });
+fs.mkdirSync('.output/server/pages/api', { recursive: true });
+
+fs.writeFileSync(
+  '.output/functions-manifest.json',
+  JSON.stringify(
+    {
+      version: 1,
+      pages: {
+        '_middleware.js': {
+          runtime: 'web',
+          env: [],
+          files: ['server/pages/_middleware.js'],
+          name: 'pages/_middleware',
+          page: '/',
+          regexp: '^/.*$',
+          sortingIndex: 1,
+        },
+      },
+    },
+    null,
+    2
+  )
+);
+
+fs.writeFileSync('.output/static/index.html', '<h1>Build Output API v2</h1>');
+
+fs.writeFileSync('.output/server/pages/about.html', '<h1>Some Site</h1>');
+
+fs.writeFileSync(
+  '.output/server/pages/api/user.js',
+  `export default function handler(request, response) {
+    response.status(200).json({
+      body: 'some user info'
+    });
+  }`
+);
+
+fs.writeFileSync(
+  '.output/server/pages/_middleware.js',
+  `
+    const getResult = (body, options) => ({
+      promise: Promise.resolve(),
+      waitUntil: Promise.resolve(),
+      response: new Response(body, options),
+    });
+
+    _ENTRIES = typeof _ENTRIES === 'undefined' ? {} : _ENTRIES;
+
+    _ENTRIES['middleware_pages/_middleware'] = {
+      default: async function ({ request }) {
+
+        return getResult('hi from the edge', {});
+
+      },
+    };
+  `
+);

packages/static-build/test/build-fixtures/10-build-output-v2/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "10-build-output-v2",
+  "private": true,
+  "scripts": {
+    "build": "node build.js"
+  }
+}

packages/static-build/test/build-fixtures/11-build-output-v1/.gitignore

@@ -0,0 +1 @@
+yarn.lock

packages/static-build/test/build-fixtures/11-build-output-v1/build.js

@@ -0,0 +1,32 @@
+const fs = require('fs');
+
+fs.mkdirSync('.vercel_build_output/static', { recursive: true });
+fs.mkdirSync('.vercel_build_output/config', { recursive: true });
+
+fs.writeFileSync(
+  '.vercel_build_output/config/functions.json',
+  JSON.stringify(
+    {
+      about: {
+        memory: 3008,
+      },
+    },
+    null,
+    2
+  )
+);
+
+fs.writeFileSync(
+  '.vercel_build_output/static/index.html',
+  '<h1>Build Output API v1</h1>'
+);
+
+fs.mkdirSync('.vercel_build_output/functions/node/about', { recursive: true });
+fs.writeFileSync(
+  '.vercel_build_output/functions/node/about/index.js',
+  `export default function handler(request, response) {
+    response.status(200).json({
+      body: 'some user info'
+    });
+  }`
+);

packages/static-build/test/build-fixtures/11-build-output-v1/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "11-build-output-v1",
+  "private": true,
+  "scripts": {
+    "build": "node build.js"
+  }
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/.gitignore

@@ -0,0 +1,94 @@
+# Created by .ignore support plugin (hsz.mobi)
+### Node template
+# Logs
+logs
+*.log
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+lib-cov
+
+# Coverage directory used by tools like istanbul
+coverage
+
+# nyc test coverage
+.nyc_output
+
+# Grunt intermediate storage (http://gruntjs.com/creating-plugins#storing-task-files)
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+bower_components
+
+# node-waf configuration
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+build/Release
+
+# Dependency directories
+node_modules/
+jspm_packages/
+
+# TypeScript v1 declaration files
+typings/
+
+# Optional npm cache directory
+.npm
+
+# Optional eslint cache
+.eslintcache
+
+# Optional REPL history
+.node_repl_history
+
+# Output of 'npm pack'
+*.tgz
+
+# Yarn Integrity file
+.yarn-integrity
+
+# dotenv environment variables file
+.env
+.env.build
+
+# parcel-bundler cache (https://parceljs.org/)
+.cache
+
+# next.js build output
+.next
+
+# nuxt.js build output
+.nuxt
+
+# Nuxt generate
+dist
+
+# vuepress build output
+.vuepress/dist
+
+# Serverless directories
+.serverless
+
+# IDE / Editor
+.idea
+
+# Service worker
+sw.*
+
+# macOS
+.DS_Store
+
+# Vim swap files
+*.swp
+
+# Vercel
+.vercel

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/.output/nitro.json

@@ -0,0 +1,7 @@
+{
+  "date": "2022-05-18T17:39:45.094Z",
+  "preset": "nitro-prerender",
+  "commands": {
+    "preview": "npx serve -s ./public"
+  }
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/.output/public/_nuxt/manifest.json

@@ -0,0 +1,8 @@
+{
+  "node_modules/nuxt/dist/app/entry.mjs": {
+    "file": "entry-51e0e8ac.mjs",
+    "src": "node_modules/nuxt/dist/app/entry.mjs",
+    "isEntry": true,
+    "css": ["entry.fec640a4.css"]
+  }
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/.vercel_build_output/static/_nuxt/manifest.json

@@ -0,0 +1,8 @@
+{
+  "node_modules/nuxt/dist/app/entry.mjs": {
+    "file": "entry-51e0e8ac.mjs",
+    "src": "node_modules/nuxt/dist/app/entry.mjs",
+    "isEntry": true,
+    "css": ["entry.fec640a4.css"]
+  }
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/.vercelignore

@@ -0,0 +1,5 @@
+README.md
+.nuxt
+.output
+node_modules
+*.log

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/README.md

@@ -0,0 +1,10 @@
+# 12-build-output-v1-conflict
+
+This fixture was built with the latest (at this time) nuxt 3 release candidate. To produce a potential Build Output API version detection conflict, the following was executed in the fixture directory and committed:
+
+- `yarn nuxi build`: produced the `.output`
+- `NOW_BUILDER=1 yarn nuxi build`: produced the `.vercel_build_output`
+
+The `NOW_BUILDER` env var is being detected by the nuxt build to know to produce the Build Output API v1 format.
+
+After creating this fixutre, `"nuxt": "3.0.0-rc.3"` was removed from the `package.json` dependencies so that it would not be installed during every test run. It's not necessary to run a test on this fixture and it was causing CI timeouts.

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/app.vue

@@ -0,0 +1,5 @@
+<template>
+  <div>
+    <NuxtWelcome />
+  </div>
+</template>

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/build.js

@@ -0,0 +1,50 @@
+const fs = require('fs');
+
+fs.mkdirSync('.vercel_build_output/static', { recursive: true });
+fs.mkdirSync('.vercel_build_output/config', { recursive: true });
+
+fs.writeFileSync(
+  '.vercel_build_output/config/functions.json',
+  JSON.stringify(
+    {
+      about: {
+        memory: 3008,
+      },
+    },
+    null,
+    2
+  )
+);
+
+fs.writeFileSync(
+  '.vercel_build_output/static/index.html',
+  '<h1>Build Output API v1</h1>'
+);
+
+fs.mkdirSync('.vercel_build_output/functions/node/about', { recursive: true });
+fs.writeFileSync(
+  '.vercel_build_output/functions/node/about/index.js',
+  `export default function handler(request, response) {
+    response.status(200).json({
+      body: 'some user info'
+    });
+  }`
+);
+
+// .output looks like a Build Output API v2 build, but some frameworks (like Nuxt) use it
+// for their own purposes
+fs.mkdirSync('.output', { recursive: true });
+fs.writeFileSync(
+  '.output/nitro.json',
+  JSON.stringify(
+    {
+      date: '2022-05-16T16:18:26.958Z',
+      preset: 'server',
+      commands: {
+        preview: 'node ./server/index.mjs',
+      },
+    },
+    null,
+    2
+  )
+);

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/nuxt.config.ts

@@ -0,0 +1,4 @@
+import { defineNuxtConfig } from 'nuxt';
+
+// https://v3.nuxtjs.org/docs/directory-structure/nuxt.config
+export default defineNuxtConfig({});

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "12-build-output-v1-conflict",
+  "private": true,
+  "scripts": {
+    "dev": "nuxi dev",
+    "build": "echo 'using already built `nuxi generate` for nuxt3'",
+    "start": "node .output/server/index.mjs"
+  },
+  "dependencies": {}
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/tsconfig.json

@@ -0,0 +1,4 @@
+{
+  // https://v3.nuxtjs.org/concepts/typescript
+  "extends": "./.nuxt/tsconfig.json"
+}

packages/static-build/test/build-fixtures/12-build-output-v1-conflict/yarn.lock

@@ -0,0 +1,4 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+

packages/static-build/test/build.test.ts

@@ -1,56 +1,149 @@
 import path from 'path';
+import { remove } from 'fs-extra';
 import { build } from '../src';
 
-describe('build()', () => {
-  jest.setTimeout(60 * 1000);
+jest.setTimeout(60 * 1000);
 
-  it('should detect Builder Output v3', async () => {
-    const workPath = path.join(
-      __dirname,
-      'build-fixtures',
-      '09-build-output-v3'
-    );
-    const buildResult = await build({
-      files: {},
-      entrypoint: 'package.json',
-      workPath,
-      config: {},
-      meta: {
-        skipDownload: true,
-        cliVersion: '0.0.0',
-      },
+describe('build()', () => {
+  describe('Build Output API v1', () => {
+    it('should detect the output format', async () => {
+      const workPath = path.join(
+        __dirname,
+        'build-fixtures',
+        '11-build-output-v1'
+      );
+
+      try {
+        const buildResult = await build({
+          files: {},
+          entrypoint: 'package.json',
+          workPath,
+          config: {},
+          meta: {
+            skipDownload: true,
+            cliVersion: '0.0.0',
+          },
+        });
+        if ('buildOutputVersion' in buildResult) {
+          throw new Error('Unexpected `buildOutputVersion` in build result');
+        }
+
+        expect(buildResult.output['index.html']).toBeTruthy();
+      } finally {
+        remove(path.join(workPath, '.vercel_build_output'));
+      }
+    });
+
+    it('should detect the v1 output format when .output exists', async () => {
+      const workPath = path.join(
+        __dirname,
+        'build-fixtures',
+        '12-build-output-v1-conflict'
+      );
+
+      try {
+        process.env.NOW_BUILDER = '1';
+        const buildResult = await build({
+          files: {},
+          entrypoint: 'package.json',
+          workPath,
+          config: {},
+          meta: {
+            skipDownload: true,
+            cliVersion: '0.0.0',
+          },
+        });
+        if ('buildOutputVersion' in buildResult) {
+          throw new Error('Unexpected `buildOutputVersion` in build result');
+        }
+
+        expect(buildResult.output['index.html']).toBeTruthy();
+      } finally {
+        delete process.env.NOW_BUILDER;
+      }
     });
-    if ('output' in buildResult) {
-      throw new Error('Unexpected `output` in build result');
-    }
-    expect(buildResult.buildOutputVersion).toEqual(3);
-    expect(buildResult.buildOutputPath).toEqual(
-      path.join(workPath, '.vercel/output')
-    );
   });
 
-  it('should throw an Error with Builder Output v3 without `vercel build`', async () => {
-    let err;
-    const workPath = path.join(
-      __dirname,
-      'build-fixtures',
-      '09-build-output-v3'
-    );
-    try {
-      await build({
+  describe('Build Output API v2', () => {
+    it('should detect the output format', async () => {
+      const workPath = path.join(
+        __dirname,
+        'build-fixtures',
+        '10-build-output-v2'
+      );
+
+      try {
+        const buildResult = await build({
+          files: {},
+          entrypoint: 'package.json',
+          workPath,
+          config: {},
+          meta: {
+            skipDownload: true,
+            cliVersion: '0.0.0',
+          },
+        });
+        if ('buildOutputVersion' in buildResult) {
+          throw new Error('Unexpected `buildOutputVersion` in build result');
+        }
+
+        expect(buildResult.output['index.html']).toBeTruthy();
+        expect(buildResult.output['middleware']).toBeTruthy();
+      } finally {
+        remove(path.join(workPath, '.output'));
+      }
+    });
+  });
+
+  describe('Build Output API v3', () => {
+    it('should detect the output format', async () => {
+      const workPath = path.join(
+        __dirname,
+        'build-fixtures',
+        '09-build-output-v3'
+      );
+      const buildResult = await build({
         files: {},
         entrypoint: 'package.json',
         workPath,
         config: {},
         meta: {
           skipDownload: true,
+          cliVersion: '0.0.0',
         },
       });
-    } catch (_err: any) {
-      err = _err;
-    }
-    expect(err.message).toEqual(
-      `Detected Build Output v3 from the "build" script, but this Deployment is not using \`vercel build\`.\nPlease set the \`ENABLE_VC_BUILD=1\` environment variable.`
-    );
+      if ('output' in buildResult) {
+        throw new Error('Unexpected `output` in build result');
+      }
+      expect(buildResult.buildOutputVersion).toEqual(3);
+      expect(buildResult.buildOutputPath).toEqual(
+        path.join(workPath, '.vercel/output')
+      );
+    });
+
+    it('should throw an Error without `vercel build`', async () => {
+      let err;
+      const workPath = path.join(
+        __dirname,
+        'build-fixtures',
+        '09-build-output-v3'
+      );
+      try {
+        await build({
+          files: {},
+          entrypoint: 'package.json',
+          workPath,
+          config: {},
+          meta: {
+            skipDownload: true,
+          },
+        });
+      } catch (_err: any) {
+        err = _err;
+      }
+      expect(err.message).toEqual(
+        `Detected Build Output v3 from the "build" script, but this Deployment is not using \`vercel build\`.\nPlease set the \`ENABLE_VC_BUILD=1\` environment variable.`
+      );
+    });
   });
 });