first commit

test/integration/middleware-build-errors/middleware.js

@@ -0,0 +1 @@
+// this will be populated by each test

test/integration/middleware-build-errors/pages/index.js

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+export default function Home() {
+  return <div>A page</div>
+}

test/integration/middleware-build-errors/test/index.test.ts

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+import { remove, writeFile } from 'fs-extra'
+import { nextBuild } from 'next-test-utils'
+import { join } from 'path'
+
+describe('Middleware validation during build', () => {
+  ;(process.env.TURBOPACK_DEV ? describe.skip : describe)(
+    'production mode',
+    () => {
+      const appDir = join(__dirname, '..')
+      const middlewareFile = join(appDir, 'middleware.js')
+      const middlewareError = 'Middleware is returning a response body'
+
+      beforeEach(() => remove(join(appDir, '.next')))
+
+      afterEach(() =>
+        writeFile(middlewareFile, '// this will be populated by each test\n')
+      )
+
+      describe.each([
+        {
+          title: 'returning a text body',
+          code: `export default function () {
+              return new Response('this is not allowed')
+            }`,
+        },
+        {
+          title: 'building body with JSON.stringify',
+          code: `export default function () {
+              return new Response(JSON.stringify({ error: 'this is not allowed' }))
+            }`,
+        },
+        {
+          title: 'building response body with a variable',
+          code: `export default function () {
+              const body = 'this is not allowed, but hard to detect with AST'
+              return new Response(body)
+            }`,
+        },
+        {
+          title: 'building response body with custom code',
+          code: `function buildResponse() {
+              return JSON.stringify({ message: 'this is not allowed, but hard to detect with AST' })
+            }
+
+            export default function () {
+              return new Response(buildResponse())
+            }`,
+        },
+        {
+          title: 'returning a text body with NextResponse',
+          code: `import { NextResponse } from 'next/server'
+            export default function () {
+              return new NextResponse('this is not allowed')
+            }`,
+        },
+      ])('given a middleware $title', ({ code }) => {
+        beforeAll(() => writeFile(middlewareFile, code))
+
+        it('does not throw an error', async () => {
+          const { stderr, code } = await nextBuild(appDir, [], {
+            stderr: true,
+            stdout: true,
+          })
+          expect(stderr).not.toMatch(middlewareError)
+          expect(code).toBe(0)
+        })
+      })
+
+      describe.each([
+        {
+          title: 'returning a null body',
+          code: `export default function () {
+              return new Response(null)
+            }`,
+        },
+        {
+          title: 'returning an undefined body',
+          code: `export default function () {
+              return new Response(undefined)
+            }`,
+        },
+      ])('given a middleware $title', ({ code }) => {
+        beforeAll(() => writeFile(middlewareFile, code))
+
+        it('builds successfully', async () => {
+          const { stderr, code } = await nextBuild(appDir, [], {
+            stderr: true,
+            stdout: true,
+          })
+          expect(stderr).not.toMatch(middlewareError)
+          expect(code).toBe(0)
+        })
+      })
+    }
+  )
+})