fix(vercel): write vercel.json as a part of setup (#10355)

Follow up to #10295. Implements
the strategy suggested in
#10295 (comment).
Still need to validate with deploy target CI.

.changesets/10355.md

@@ -0,0 +1,3 @@
+- fix(vercel): write `vercel.json` as a part of setup (#10355) by @jtoar
+
+This PR smooths initial deploys to Vercel by writing a `vercel.json` file that specifies an env var that enables Corepack. Users that already successfully deploy to Vercel don't need to introduce this file.

packages/cli/src/commands/setup/deploy/providers/vercel.js

@@ -1,28 +1,33 @@
-// import terminalLink from 'terminal-link'
+import path from 'path'
+
 import { Listr } from 'listr2'
 
 import { recordTelemetryAttributes } from '@redwoodjs/cli-helpers'
 import { errorTelemetry } from '@redwoodjs/telemetry'
 
-import { printSetupNotes } from '../../../../lib'
+import { getPaths, printSetupNotes, writeFile } from '../../../../lib'
 import c from '../../../../lib/colors'
 import { updateApiURLTask } from '../helpers'
 
 export const command = 'vercel'
 export const description = 'Setup Vercel deploy'
 
-const notes = [
-  'You are ready to deploy to Vercel!',
-  'See: https://redwoodjs.com/docs/deploy#vercel-deploy',
-]
-
-export const handler = async () => {
+export async function handler(options) {
   recordTelemetryAttributes({
     command: 'setup deploy vercel',
   })
-  const tasks = new Listr([updateApiURLTask('/api'), printSetupNotes(notes)], {
-    rendererOptions: { collapseSubtasks: false },
-  })
+
+  const tasks = new Listr(
+    [
+      updateApiURLTask('/api'),
+      writeVercelConfigTask({ overwriteExisting: options.force }),
+      printSetupNotes(notes),
+    ],
+    {
+      rendererOptions: { collapseSubtasks: false },
+    },
+  )
+
   try {
     await tasks.run()
   } catch (e) {
@@ -31,3 +36,30 @@ export const handler = async () => {
     process.exit(e?.exitCode || 1)
   }
 }
+
+function writeVercelConfigTask({ overwriteExisting = false } = {}) {
+  return {
+    title: 'Writing vercel.json...',
+    task: (_ctx, task) => {
+      writeFile(
+        path.join(getPaths().base, 'vercel.json'),
+        JSON.stringify(vercelConfig, null, 2),
+        { overwriteExisting },
+        task,
+      )
+    },
+  }
+}
+
+const vercelConfig = {
+  build: {
+    env: {
+      ENABLE_EXPERIMENTAL_COREPACK: 1,
+    },
+  },
+}
+
+const notes = [
+  'You are ready to deploy to Vercel!',
+  'See: https://redwoodjs.com/docs/deploy#vercel-deploy',
+]