next-upgrade: prompt (un)install only when there's a change (#71308)

### Why?

When running next-upgrade, `next-request-geo-ip` requires to install
`@vercel/functions` and `built-in-next-font` makes `@next/font` no
longer needed. We added a prompt to ask user whether to (un)install it
at #71038 but it prompts even if
there were no transform occurred.

This is unnecessary layer so we only prompt when there's a change caused
from the codemod.

### No Modification


https://github.com/user-attachments/assets/3acfdb24-c8e7-4189-9c81-4765ce748822

### With Modification


https://github.com/user-attachments/assets/f44a8b1c-c75a-4446-afc8-f74111de939d

---------

.eslintignore

@@ -23,6 +23,7 @@ packages/react-dev-overlay/lib/**
 .github/actions/next-stats-action/.work
 packages/next-codemod/transforms/__testfixtures__/**/*
 packages/next-codemod/transforms/__tests__/**/*
+packages/next-codemod/bin/__testfixtures__/**/*
 packages/next-codemod/**/*.js
 packages/next-codemod/**/*.d.ts
 packages/next-env/**/*.d.ts

packages/next-codemod/bin/__testfixtures__/geo-ip-usage/README.md

@@ -0,0 +1 @@
+Installs `@vercel/functions`

packages/next-codemod/bin/__testfixtures__/geo-ip-usage/app/route.tsx

@@ -0,0 +1,8 @@
+// @ts-nocheck
+import { type NextRequest, NextResponse } from 'next/server'
+
+export function GET(request: NextRequest) {
+  const geo = request.geo
+  const ip = request.ip
+  return NextResponse.json({ geo, ip })
+}

packages/next-codemod/bin/__testfixtures__/geo-ip-usage/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "geo-ip-usage",
+  "scripts": {
+    "dev": "next dev --turbo"
+  },
+  "dependencies": {
+    "next": "15.0.0-canary.152",
+    "react": "19.0.0-rc-94e652d5-20240912",
+    "react-dom": "19.0.0-rc-94e652d5-20240912"
+  }
+}

packages/next-codemod/bin/__testfixtures__/no-geo-ip-usage/README.md

@@ -0,0 +1 @@
+Should not install `@vercel/functions`

packages/next-codemod/bin/__testfixtures__/no-geo-ip-usage/app/page.tsx

@@ -0,0 +1,3 @@
+export default function Page() {
+  return null
+}

packages/next-codemod/bin/__testfixtures__/no-geo-ip-usage/package.json

@@ -0,0 +1,11 @@
+{
+  "name": "no-geo-ip-usage",
+  "scripts": {
+    "dev": "next dev --turbo"
+  },
+  "dependencies": {
+    "next": "15.0.0-canary.152",
+    "react": "19.0.0-rc-94e652d5-20240912",
+    "react-dom": "19.0.0-rc-94e652d5-20240912"
+  }
+}

packages/next-codemod/bin/transform.ts

@@ -1,6 +1,7 @@
 import execa from 'execa'
 import globby from 'globby'
 import prompts from 'prompts'
+import stripAnsi from 'strip-ansi'
 import { join } from 'node:path'
 import { installPackages, uninstallPackage } from '../lib/handle-package'
 import {
@@ -79,6 +80,25 @@ export async function runTransform(
     transformer = res.transformer
   }
 
+  if (transformer === 'next-request-geo-ip') {
+    const { isAppDeployedToVercel } = await prompts(
+      {
+        type: 'confirm',
+        name: 'isAppDeployedToVercel',
+        message:
+          'Is your app deployed to Vercel? (Required to apply the selected codemod)',
+        initial: true,
+      },
+      { onCancel }
+    )
+    if (!isAppDeployedToVercel) {
+      console.log(
+        'Skipping codemod "next-request-geo-ip" as your app is not deployed to Vercel.'
+      )
+      return
+    }
+  }
+
   const filesExpanded = expandFilePathsIfNeeded([directory])
 
   if (!filesExpanded.length) {
@@ -126,40 +146,89 @@ export async function runTransform(
 
   console.log(`Executing command: jscodeshift ${args.join(' ')}`)
 
-  const result = execa.sync(jscodeshiftExecutable, args, {
-    stdio: 'inherit',
-    stripFinalNewline: false,
+  const execaChildProcess = execa(jscodeshiftExecutable, args, {
+    // include ANSI color codes
+    // Note: execa merges env with existing env by default.
+    env: process.stdout.isTTY ? { FORCE_COLOR: 'true' } : {},
   })
 
-  if (result.failed) {
-    throw new Error(`jscodeshift exited with code ${result.exitCode}`)
-  }
+  // "\n" + "a\n" + "b\n"
+  let lastThreeLineBreaks = ''
 
-  if (!dry && transformer === 'built-in-next-font') {
-    const { uninstallNextFont } = await prompts({
-      type: 'confirm',
-      name: 'uninstallNextFont',
-      message: 'Do you want to uninstall `@next/font`?',
-      initial: true,
+  if (execaChildProcess.stdout) {
+    execaChildProcess.stdout.pipe(process.stdout)
+    execaChildProcess.stderr.pipe(process.stderr)
+
+    // The last two lines contain the successful transformation count as "N ok".
+    // To save memory, we "slide the window" to keep only the last three line breaks.
+    // We save three line breaks because the EOL is always "\n".
+    execaChildProcess.stdout.on('data', (chunk) => {
+      lastThreeLineBreaks += chunk.toString('utf-8')
+
+      let cutoff = lastThreeLineBreaks.length
+
+      // Note: the stdout ends with "\n".
+      // "foo\n" + "bar\n" + "baz\n" -> "\nbar\nbaz\n"
+      // "\n" + "foo\n" + "bar\n" -> "\nfoo\nbar\n"
+
+      for (let i = 0; i < 3; i++) {
+        cutoff = lastThreeLineBreaks.lastIndexOf('\n', cutoff) - 1
+      }
+
+      if (cutoff > 0 && cutoff < lastThreeLineBreaks.length) {
+        lastThreeLineBreaks = lastThreeLineBreaks.slice(cutoff + 1)
+      }
     })
+  }
+
+  try {
+    const result = await execaChildProcess
+
+    if (result.failed) {
+      throw new Error(`jscodeshift exited with code ${result.exitCode}`)
+    }
+  } catch (error) {
+    throw error
+  }
+
+  // With ANSI color codes, it will be "\x1B[39m\x1B[32m0 ok".
+  // Without, it will be "0 ok".
+  const targetOkLine = lastThreeLineBreaks.split('\n').at(-3)
+
+  if (!targetOkLine.endsWith('ok')) {
+    throw new Error(
+      `Failed to parse the successful transformation count "${targetOkLine}". This is a bug in the codemod tool.`
+    )
+  }
+
+  const stripped = stripAnsi(targetOkLine)
+  // "N ok" -> "N"
+  const parsedNum = parseInt(stripped.split(' ')[0], 10)
+  const hasChanges = parsedNum > 0
+
+  if (!dry && transformer === 'built-in-next-font' && hasChanges) {
+    const { uninstallNextFont } = await prompts(
+      {
+        type: 'confirm',
+        name: 'uninstallNextFont',
+        message:
+          '`built-in-next-font` should have removed all usages of `@next/font`. Do you want to uninstall `@next/font`?',
+        initial: true,
+      },
+      { onCancel }
+    )
 
     if (uninstallNextFont) {
       console.log('Uninstalling `@next/font`')
       uninstallPackage('@next/font')
     }
   }
 
-  if (!dry && transformer === 'next-request-geo-ip') {
-    const { installVercelFunctions } = await prompts({
-      type: 'confirm',
-      name: 'installVercelFunctions',
-      message: 'Do you want to install `@vercel/functions`?',
-      initial: true,
-    })
-
-    if (installVercelFunctions) {
-      console.log('Installing `@vercel/functions`...')
-      installPackages(['@vercel/functions'])
-    }
+  // When has changes, it requires `@vercel/functions`, so skip prompt.
+  if (!dry && transformer === 'next-request-geo-ip' && hasChanges) {
+    console.log(
+      'Installing `@vercel/functions` because the `next-request-geo-ip` made changes.'
+    )
+    installPackages(['@vercel/functions'])
   }
 }

packages/next-codemod/package.json

@@ -17,7 +17,8 @@
     "jscodeshift": "17.0.0",
     "picocolors": "1.0.0",
     "prompts": "2.4.2",
-    "semver": "7.6.3"
+    "semver": "7.6.3",
+    "strip-ansi": "6.0.0"
   },
   "files": [
     "transforms/*.js",