Improve initial setup with new App Router TypeScript project

.github/workflows/build_reusable.yml

@@ -133,6 +133,12 @@ jobs:
       # clean up any previous artifacts to avoid hitting disk space limits
       - run: git clean -xdf && rm -rf /tmp/next-repo-*; rm -rf /tmp/next-install-* /tmp/yarn-* /tmp/ncc-cache target
 
+      # Configure a git user so that Create Next App can initialize git repos during integration tests.
+      - name: Set CI git user
+        run: |
+          git config --global user.name "vercel-ci-bot"
+          git config --global user.email "infra+ci@vercel.com"
+
       - run: cargo clean
         if: ${{ inputs.skipNativeBuild != 'yes' || inputs.needsNextest == 'yes' || inputs.needsRust == 'yes' }}
 

packages/create-next-app/templates/app-tw/ts/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "target": "ES2017",
     "lib": ["dom", "dom.iterable", "esnext"],
     "allowJs": true,
     "skipLibCheck": true,

packages/create-next-app/templates/app/ts/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "target": "ES2017",
     "lib": ["dom", "dom.iterable", "esnext"],
     "allowJs": true,
     "skipLibCheck": true,

packages/create-next-app/templates/default-tw/ts/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "target": "ES2017",
     "lib": ["dom", "dom.iterable", "esnext"],
     "allowJs": true,
     "skipLibCheck": true,

packages/create-next-app/templates/default/ts/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "compilerOptions": {
+    "target": "ES2017",
     "lib": ["dom", "dom.iterable", "esnext"],
     "allowJs": true,
     "skipLibCheck": true,

packages/next/src/lib/typescript/writeConfigurationDefaults.test.ts

@@ -0,0 +1,257 @@
+import { mkdtemp, writeFile, readFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+// eslint-disable-next-line import/no-extraneous-dependencies
+import ts from 'typescript'
+import { writeConfigurationDefaults } from './writeConfigurationDefaults'
+
+describe('writeConfigurationDefaults()', () => {
+  let consoleLogSpy: jest.SpyInstance
+  let distDir: string
+  let hasAppDir: boolean
+  let tmpDir: string
+  let tsConfigPath: string
+  let isFirstTimeSetup: boolean
+  let hasPagesDir: boolean
+
+  beforeEach(async () => {
+    consoleLogSpy = jest.spyOn(console, 'log').mockImplementation()
+    distDir = '.next'
+    tmpDir = await mkdtemp(join(tmpdir(), 'nextjs-test-'))
+    tsConfigPath = join(tmpDir, 'tsconfig.json')
+    isFirstTimeSetup = false
+  })
+
+  afterEach(() => {
+    consoleLogSpy.mockRestore()
+  })
+
+  describe('appDir', () => {
+    beforeEach(() => {
+      hasAppDir = true
+      hasPagesDir = false
+    })
+
+    it('applies suggested and mandatory defaults to existing tsconfig.json and logs them', async () => {
+      await writeFile(tsConfigPath, JSON.stringify({ compilerOptions: {} }), {
+        encoding: 'utf8',
+      })
+
+      await writeConfigurationDefaults(
+        ts,
+        tsConfigPath,
+        isFirstTimeSetup,
+        hasAppDir,
+        distDir,
+        hasPagesDir
+      )
+
+      const tsConfig = await readFile(tsConfigPath, { encoding: 'utf8' })
+
+      expect(JSON.parse(tsConfig)).toMatchInlineSnapshot(`
+      {
+        "compilerOptions": {
+          "allowJs": true,
+          "esModuleInterop": true,
+          "incremental": true,
+          "isolatedModules": true,
+          "jsx": "preserve",
+          "lib": [
+            "dom",
+            "dom.iterable",
+            "esnext",
+          ],
+          "module": "esnext",
+          "moduleResolution": "node",
+          "noEmit": true,
+          "plugins": [
+            {
+              "name": "next",
+            },
+          ],
+          "resolveJsonModule": true,
+          "skipLibCheck": true,
+          "strict": false,
+          "target": "ES2017",
+        },
+        "exclude": [
+          "node_modules",
+        ],
+        "include": [
+          "next-env.d.ts",
+          ".next/types/**/*.ts",
+          "**/*.ts",
+          "**/*.tsx",
+        ],
+      }
+    `)
+
+      expect(
+        consoleLogSpy.mock.calls
+          .flat()
+          .join('\n')
+          // eslint-disable-next-line no-control-regex
+          .replace(/\x1B\[\d+m/g, '') // remove color control characters
+      ).toMatchInlineSnapshot(`
+      "
+
+      We detected TypeScript in your project and reconfigured your tsconfig.json file for you. Strict-mode is set to false by default.
+
+      The following suggested values were added to your tsconfig.json. These values can be changed to fit your project's needs:
+
+
+      	- target was set to ES2017 (For top-level \`await\`. Note: Next.js only polyfills for the esmodules target.)
+
+      	- lib was set to dom,dom.iterable,esnext
+
+      	- allowJs was set to true
+
+      	- skipLibCheck was set to true
+
+      	- strict was set to false
+
+      	- noEmit was set to true
+
+      	- incremental was set to true
+
+      	- include was set to ['next-env.d.ts', '.next/types/**/*.ts', '**/*.ts', '**/*.tsx']
+
+      	- plugins was updated to add { name: 'next' }
+
+      	- exclude was set to ['node_modules']
+
+
+      The following mandatory changes were made to your tsconfig.json:
+
+
+      	- module was set to esnext (for dynamic import() support)
+
+      	- esModuleInterop was set to true (requirement for SWC / babel)
+
+      	- moduleResolution was set to node (to match webpack resolution)
+
+      	- resolveJsonModule was set to true (to match webpack resolution)
+
+      	- isolatedModules was set to true (requirement for SWC / Babel)
+
+      	- jsx was set to preserve (next.js implements its own optimized jsx transform)
+      "
+    `)
+    })
+
+    it('does not warn about disabled strict mode if strict mode was already enabled', async () => {
+      await writeFile(
+        tsConfigPath,
+        JSON.stringify({ compilerOptions: { strict: true } }),
+        { encoding: 'utf8' }
+      )
+
+      await writeConfigurationDefaults(
+        ts,
+        tsConfigPath,
+        isFirstTimeSetup,
+        hasAppDir,
+        distDir,
+        hasPagesDir
+      )
+
+      expect(
+        consoleLogSpy.mock.calls
+          .flat()
+          .join('\n')
+          // eslint-disable-next-line no-control-regex
+          .replace(/\x1B\[\d+m/g, '') // remove color control characters
+      ).not.toMatch('Strict-mode is set to false by default.')
+    })
+
+    describe('with tsconfig extends', () => {
+      let tsConfigBasePath: string
+      let nextAppTypes: string
+
+      beforeEach(() => {
+        tsConfigBasePath = join(tmpDir, 'tsconfig.base.json')
+        nextAppTypes = `${distDir}/types/**/*.ts`
+      })
+
+      it('should support empty includes when base provides it', async () => {
+        const include = ['**/*.ts', '**/*.tsx', nextAppTypes]
+        const content = { extends: './tsconfig.base.json' }
+        const baseContent = { include }
+
+        await writeFile(tsConfigPath, JSON.stringify(content, null, 2))
+        await writeFile(tsConfigBasePath, JSON.stringify(baseContent, null, 2))
+
+        await expect(
+          writeConfigurationDefaults(
+            ts,
+            tsConfigPath,
+            isFirstTimeSetup,
+            hasAppDir,
+            distDir,
+            hasPagesDir
+          )
+        ).resolves.not.toThrow()
+
+        const output = await readFile(tsConfigPath, 'utf-8')
+        const parsed = JSON.parse(output)
+
+        expect(parsed.include).toBeUndefined()
+      })
+
+      it('should replace includes when base is missing appTypes', async () => {
+        const include = ['**/*.ts', '**/*.tsx']
+        const content = { extends: './tsconfig.base.json' }
+        const baseContent = { include }
+
+        await writeFile(tsConfigPath, JSON.stringify(content, null, 2))
+        await writeFile(tsConfigBasePath, JSON.stringify(baseContent, null, 2))
+
+        await expect(
+          writeConfigurationDefaults(
+            ts,
+            tsConfigPath,
+            isFirstTimeSetup,
+            hasAppDir,
+            distDir,
+            hasPagesDir
+          )
+        ).resolves.not.toThrow()
+
+        const output = await readFile(tsConfigPath, 'utf8')
+        const parsed = JSON.parse(output)
+
+        expect(parsed.include.sort()).toMatchInlineSnapshot(`
+          [
+            "**/*.ts",
+            "**/*.tsx",
+            ".next/types/**/*.ts",
+          ]
+        `)
+      })
+
+      it('should not add strictNullChecks if base provides it', async () => {
+        const content = { extends: './tsconfig.base.json' }
+
+        const baseContent = {
+          compilerOptions: { strictNullChecks: true, strict: true },
+        }
+
+        await writeFile(tsConfigPath, JSON.stringify(content, null, 2))
+        await writeFile(tsConfigBasePath, JSON.stringify(baseContent, null, 2))
+
+        await writeConfigurationDefaults(
+          ts,
+          tsConfigPath,
+          isFirstTimeSetup,
+          hasAppDir,
+          distDir,
+          hasPagesDir
+        )
+        const output = await readFile(tsConfigPath, 'utf8')
+        const parsed = JSON.parse(output)
+
+        expect(parsed.compilerOptions.strictNullChecks).toBeUndefined()
+      })
+    })
+  })
+})

packages/next/src/lib/typescript/writeConfigurationDefaults.ts

@@ -176,9 +176,7 @@ export async function writeConfigurationDefaults(
           cyan(optionKey) +
             ' was set to ' +
             bold(check.suggested) +
-            check.reason
-            ? ` (${check.reason})`
-            : ''
+            (check.reason ? ` (${check.reason})` : '')
         )
       }
     } else if ('value' in check) {
@@ -337,8 +335,13 @@ export async function writeConfigurationDefaults(
   Log.info(
     `We detected TypeScript in your project and reconfigured your ${cyan(
       'tsconfig.json'
-    )} file for you. Strict-mode is set to ${cyan('false')} by default.`
+    )} file for you.${
+      userTsConfig.compilerOptions?.strict
+        ? ''
+        : ` Strict-mode is set to ${cyan('false')} by default.`
+    }`
   )
+
   if (suggestedActions.length) {
     Log.info(
       `The following suggested values were added to your ${cyan(

test/development/acceptance-app/fixtures/app-hmr-changes/tsconfig.json

@@ -14,8 +14,13 @@
     "resolveJsonModule": true,
     "isolatedModules": true,
     "incremental": true,
-    "baseUrl": "."
+    "baseUrl": ".",
+    "plugins": [
+      {
+        "name": "next"
+      }
+    ]
   },
   "exclude": ["node_modules"],
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"]
+  "include": ["**/*.ts", "**/*.tsx", "next-env.d.ts", ".next/types/**/*.ts"]
 }

test/development/app-dir/experimental-lightningcss/tsconfig.json

@@ -16,7 +16,8 @@
       {
         "name": "next"
       }
-    ]
+    ],
+    "target": "ES2017"
   },
   "include": ["next-env.d.ts", ".next/types/**/*.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]

test/development/basic/define-class-fields/fixture/tsconfig.json

@@ -15,5 +15,7 @@
     "moduleResolution": "bundler",
     "resolveJsonModule": true,
     "isolatedModules": true
-  }
+  },
+  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx"],
+  "exclude": ["node_modules"]
 }

test/e2e/app-dir/edge-runtime-node-compatibility/tsconfig.json

@@ -18,7 +18,8 @@
         "name": "next"
       }
     ],
-    "strictNullChecks": true
+    "strictNullChecks": true,
+    "target": "ES2017"
   },
   "include": ["next-env.d.ts", ".next/types/**/*.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]

test/e2e/app-dir/interception-middleware-rewrite/tsconfig.json

@@ -17,7 +17,8 @@
       {
         "name": "next"
       }
-    ]
+    ],
+    "target": "ES2017"
   },
   "include": ["next-env.d.ts", ".next/types/**/*.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]

test/e2e/app-dir/metadata-suspense/tsconfig.json

@@ -17,7 +17,8 @@
       {
         "name": "next"
       }
-    ]
+    ],
+    "target": "ES2017"
   },
   "include": ["next-env.d.ts", ".next/types/**/*.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]

test/e2e/app-dir/modularizeimports/tsconfig.json

@@ -18,7 +18,8 @@
         "name": "next"
       }
     ],
-    "strictNullChecks": true
+    "strictNullChecks": true,
+    "target": "ES2017"
   },
   "include": ["next-env.d.ts", ".next/types/**/*.ts", "**/*.ts", "**/*.tsx"],
   "exclude": ["node_modules"]