[cli] Normalize "src" property in vc build (#7943)

This matches the production behavior.

packages/cli/src/commands/build.ts

@@ -1,7 +1,7 @@
 import fs from 'fs-extra';
 import chalk from 'chalk';
 import dotenv from 'dotenv';
-import { join, relative } from 'path';
+import { join, normalize, relative } from 'path';
 import {
   detectBuilders,
   normalizePath,
@@ -15,6 +15,7 @@ import {
   BuildResultV2,
   BuildResultV2Typical,
   BuildResultV3,
+  NowBuildError,
 } from '@vercel/build-utils';
 import minimatch from 'minimatch';
 import {
@@ -475,17 +476,33 @@ export default async function main(client: Client): Promise<number> {
 }
 
 function expandBuild(files: string[], build: Builder): Builder[] {
-  if (!build.src) return [];
+  if (!build.use) {
+    throw new NowBuildError({
+      code: `invalid_build_specification`,
+      message: 'Field `use` is missing in build specification',
+      link: 'https://vercel.com/docs/configuration#project/builds',
+      action: 'View Documentation',
+    });
+  }
 
-  let pattern = build.src;
+  let src = normalize(build.src || '**');
-  if (pattern[0] === '/') {
+  if (src === '.' || src === './') {
+    throw new NowBuildError({
+      code: `invalid_build_specification`,
+      message: 'A build `src` path resolves to an empty string',
+      link: 'https://vercel.com/docs/configuration#project/builds',
+      action: 'View Documentation',
+    });
+  }
+
+  if (src[0] === '/') {
     // Remove a leading slash so that the globbing is relative
     // to `cwd` instead of the root of the filesystem.
-    pattern = pattern.substring(1);
+    src = src.substring(1);
   }
 
   const matches = files.filter(
-    name => name === pattern || minimatch(name, pattern, { dot: true })
+    name => name === src || minimatch(name, src, { dot: true })
   );
 
   return matches.map(m => {

packages/cli/test/fixtures/unit/commands/build/normalize-src/.vercel/project.json

@@ -0,0 +1,7 @@
+{
+  "orgId": ".",
+  "projectId": ".",
+  "settings": {
+    "framework": null
+  }
+}

packages/cli/test/fixtures/unit/commands/build/normalize-src/server.js

@@ -0,0 +1 @@
+module.exports = (req, res) => res.end('Vercel');

packages/cli/test/fixtures/unit/commands/build/normalize-src/vercel.json

@@ -0,0 +1,15 @@
+{
+  "version": 2,
+  "builds": [
+    {
+      "src": "./server.js",
+      "use": "@vercel/node"
+    }
+  ],
+  "routes": [
+    {
+      "src": "/(.*)",
+      "dest": "/server.js"
+    }
+  ]
+}

packages/cli/test/unit/commands/build.test.ts

@@ -111,6 +111,56 @@ describe('build', () => {
     }
   });
 
+  it('should normalize "src" path in `vercel.json`', async () => {
+    const cwd = fixture('normalize-src');
+    const output = join(cwd, '.vercel/output');
+    try {
+      process.chdir(cwd);
+      const exitCode = await build(client);
+      expect(exitCode).toEqual(0);
+
+      // `builds.json` says that "@vercel/node" was run
+      const builds = await fs.readJSON(join(output, 'builds.json'));
+      expect(builds).toMatchObject({
+        target: 'preview',
+        builds: [
+          {
+            require: '@vercel/node',
+            apiVersion: 3,
+            use: '@vercel/node',
+            src: 'server.js',
+          },
+        ],
+      });
+
+      // `config.json` includes "route" from `vercel.json`
+      const config = await fs.readJSON(join(output, 'config.json'));
+      expect(config).toMatchObject({
+        version: 3,
+        routes: [
+          {
+            src: '^/(.*)$',
+            dest: '/server.js',
+          },
+        ],
+      });
+
+      // "static" directory is empty
+      const hasStaticFiles = await fs.pathExists(join(output, 'static'));
+      expect(
+        hasStaticFiles,
+        'Expected ".vercel/output/static" to not exist'
+      ).toEqual(false);
+
+      // "functions" directory has output Function
+      const functions = await fs.readdir(join(output, 'functions'));
+      expect(functions.sort()).toEqual(['server.js.func']);
+    } finally {
+      process.chdir(originalCwd);
+      delete process.env.__VERCEL_BUILD_RUNNING;
+    }
+  });
+
   it('should build with 3rd party Builder', async () => {
     const cwd = fixture('third-party-builder');
     const output = join(cwd, '.vercel/output');