Add configuration flags to disable integrated type checker

packages/next/README.md

@@ -2316,6 +2316,22 @@ To learn more about TypeScript checkout its [documentation](https://www.typescri
 > **Note**: Next.js does not enable TypeScript's `strict` mode by default.
 > When you feel comfortable with TypeScript, you may turn this option on in your `tsconfig.json`.
 
+> **Note**: By default, Next.js reports TypeScript errors during development for pages you are actively working on.
+> TypeScript errors for inactive pages do not block the development process.
+> Trying to run `next build` for an app that has TypeScript errors on any page will fail.
+> 
+> If you don't want to leverage this behavior and prefer to do type checks manually, set the following options in your `next.config.js`:
+>
+> ```js
+> // next.config.js
+> module.exports = {
+>   typescript: {
+>     ignoreDevErrors: true,
+>     ignoreBuildErrors: true,
+>   },
+> }
+> ```
+
 ### Exported types
 
 Next.js provides `NextPage` type that can be used for pages in the `pages` directory. `NextPage` adds definitions for [`getInitialProps`](#fetching-data-and-component-lifecycle) so that it can be used without any extra typing needed.

packages/next/build/output/store.ts

@@ -78,7 +78,7 @@ store.subscribe(state => {
   }
 
   if (state.typeChecking) {
-    Log.info('bundled successfully, waiting for typecheck results ...')
+    Log.info('bundled successfully, waiting for typecheck results...')
     return
   }
 

packages/next/build/webpack-config.ts

@@ -126,6 +126,9 @@ export default async function getBaseWebpackConfig(
   const useTypeScript = Boolean(
     typeScriptPath && (await fileExists(tsConfigPath))
   )
+  const ignoreTypeScriptErrors = dev
+    ? config.typescript && config.typescript.ignoreDevErrors
+    : config.typescript && config.typescript.ignoreBuildErrors
 
   const resolveConfig = {
     // Disable .mjs for node_modules bundling
@@ -845,6 +848,7 @@ export default async function getBaseWebpackConfig(
         }),
       !isServer &&
         useTypeScript &&
+        !ignoreTypeScriptErrors &&
         new ForkTsCheckerWebpackPlugin(
           PnpWebpackPlugin.forkTsCheckerOptions({
             typescript: typeScriptPath,

packages/next/server/hot-reloader.ts

@@ -349,11 +349,13 @@ export default class HotReloader {
   async prepareBuildTools(multiCompiler: webpack.MultiCompiler) {
     const tsConfigPath = join(this.dir, 'tsconfig.json')
     const useTypeScript = await fileExists(tsConfigPath)
+    const ignoreTypeScriptErrors =
+      this.config.typescript && this.config.typescript.ignoreDevErrors
 
     watchCompilers(
       multiCompiler.compilers[0],
       multiCompiler.compilers[1],
-      useTypeScript,
+      useTypeScript && !ignoreTypeScriptErrors,
       ({ errors, warnings }) => this.send('typeChecked', { errors, warnings })
     )
 

test/integration/typescript-ignore-errors/next.config.js

@@ -0,0 +1 @@
+module.exports = {}

test/integration/typescript-ignore-errors/pages/index.tsx

@@ -0,0 +1,2 @@
+// Below type error is intentional, it helps check typescript → ignoreDevErrors / ignoreBuildErrors flags in next.config.js
+export default (): boolean => 'Index page'

test/integration/typescript-ignore-errors/test/index.test.js

@@ -0,0 +1,84 @@
+/* eslint-env jest */
+/* global jasmine */
+import { join } from 'path'
+import {
+  renderViaHTTP,
+  nextBuild,
+  findPort,
+  launchApp,
+  killApp,
+  File
+} from 'next-test-utils'
+
+jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
+
+const appDir = join(__dirname, '..')
+const nextConfigFile = new File(join(appDir, 'next.config.js'))
+
+describe('TypeScript with error handling options', () => {
+  for (const ignoreDevErrors of [false, true]) {
+    for (const ignoreBuildErrors of [false, true]) {
+      describe(`ignoreDevErrors: ${ignoreDevErrors}, ignoreBuildErrors: ${ignoreBuildErrors}`, () => {
+        beforeAll(() => {
+          const nextConfig = {
+            typescript: { ignoreDevErrors, ignoreBuildErrors }
+          }
+          nextConfigFile.replace('{}', JSON.stringify(nextConfig))
+        })
+        afterAll(() => {
+          nextConfigFile.restore()
+        })
+
+        it(
+          ignoreDevErrors
+            ? 'Next renders the page in dev despite type errors'
+            : 'Next dev does not render the page in dev because of type errors',
+          async () => {
+            let app
+            let output = ''
+            try {
+              const appPort = await findPort()
+              app = await launchApp(appDir, appPort, {
+                onStdout: msg => (output += msg),
+                onStderr: msg => (output += msg)
+              })
+              await renderViaHTTP(appPort, '')
+
+              if (ignoreDevErrors) {
+                expect(output).not.toContain('waiting for typecheck results...')
+                expect(output).not.toContain("not assignable to type 'boolean'")
+              } else {
+                expect(output).toContain('waiting for typecheck results...')
+                expect(output).toContain("not assignable to type 'boolean'")
+              }
+            } finally {
+              await killApp(app)
+            }
+          }
+        )
+
+        it(
+          ignoreBuildErrors
+            ? 'Next builds the application despite type errors'
+            : 'Next fails to build the application despite type errors',
+          async () => {
+            const { stdout, stderr } = await nextBuild(appDir, [], {
+              stdout: true,
+              stderr: true
+            })
+
+            if (ignoreBuildErrors) {
+              expect(stdout).toContain('Compiled successfully')
+              expect(stderr).not.toContain('Failed to compile.')
+              expect(stderr).not.toContain("not assignable to type 'boolean'")
+            } else {
+              expect(stdout).not.toContain('Compiled successfully')
+              expect(stderr).toContain('Failed to compile.')
+              expect(stderr).toContain("not assignable to type 'boolean'")
+            }
+          }
+        )
+      })
+    }
+  }
+})

test/integration/typescript-ignore-errors/tsconfig.json

@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "module": "esnext",
+    "jsx": "preserve",
+    "target": "es5",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "noEmit": true,
+    "moduleResolution": "node",
+    "resolveJsonModule": true,
+    "isolatedModules": true
+  },
+  "exclude": ["node_modules"],
+  "include": ["next-env.d.ts", "pages"]
+}

test/integration/typescript/test/index.test.js

@@ -17,6 +17,11 @@ jasmine.DEFAULT_TIMEOUT_INTERVAL = 1000 * 60 * 2
 const appDir = join(__dirname, '..')
 let appPort
 let app
+let output
+
+const handleOutput = msg => {
+  output += msg
+}
 
 async function get$ (path, query) {
   const html = await renderViaHTTP(appPort, path, query)
@@ -26,8 +31,12 @@ async function get$ (path, query) {
 describe('TypeScript Features', () => {
   describe('default behavior', () => {
     beforeAll(async () => {
+      output = ''
       appPort = await findPort()
-      app = await launchApp(appDir, appPort)
+      app = await launchApp(appDir, appPort, {
+        onStdout: handleOutput,
+        onStderr: handleOutput
+      })
     })
     afterAll(() => killApp(app))
 
@@ -36,6 +45,10 @@ describe('TypeScript Features', () => {
       expect($('body').text()).toMatch(/Hello World/)
     })
 
+    it('should report type checking to stdout', async () => {
+      expect(output).toContain('waiting for typecheck results...')
+    })
+
     it('should not fail to render when an inactive page has an error', async () => {
       await killApp(app)
       let evilFile = join(appDir, 'pages', 'evil.tsx')