Preserve next-env.d.ts line ending (vercel#28100)

* Preserve `next-env.d.ts` line ending

Prevent next from changing already existing line ending on
`next-env.d.ts` for no good reason

* Update comparison

Co-authored-by: Steven <[email protected]>

* Update checks and add tests

* update test

Co-authored-by: Steven <[email protected]>
Co-authored-by: [email protected] <[email protected]>

packages/next/lib/typescript/writeAppTypeDeclarations.ts

@@ -1,7 +1,6 @@
-import { promises as fs } from 'fs'
 import os from 'os'
 import path from 'path'
-import { fileExists } from '../file-exists'
+import { promises as fs } from 'fs'
 
 export async function writeAppTypeDeclarations(
   baseDir: string,
@@ -10,27 +9,41 @@ export async function writeAppTypeDeclarations(
   // Reference `next` types
   const appTypeDeclarations = path.join(baseDir, 'next-env.d.ts')
 
+  // Defaults EOL to system default
+  let eol = os.EOL
+  let currentContent: string | undefined
+
+  try {
+    currentContent = await fs.readFile(appTypeDeclarations, 'utf8')
+    // If file already exists then preserve its line ending
+    const lf = currentContent.indexOf('\n', /* skip first so we can lf - 1 */ 1)
+
+    if (lf !== -1) {
+      if (currentContent[lf - 1] === '\r') {
+        eol = '\r\n'
+      } else {
+        eol = '\n'
+      }
+    }
+  } catch (err) {}
+
   const content =
     '/// <reference types="next" />' +
-    os.EOL +
+    eol +
     '/// <reference types="next/types/global" />' +
-    os.EOL +
+    eol +
     (imageImportsEnabled
-      ? '/// <reference types="next/image-types/global" />' + os.EOL
+      ? '/// <reference types="next/image-types/global" />' + eol
       : '') +
-    os.EOL +
+    eol +
     '// NOTE: This file should not be edited' +
-    os.EOL +
+    eol +
     '// see https://nextjs.org/docs/basic-features/typescript for more information.' +
-    os.EOL
+    eol
 
-  // Avoids a write for read-only filesystems
-  if (
-    (await fileExists(appTypeDeclarations)) &&
-    (await fs.readFile(appTypeDeclarations, 'utf8')) === content
-  ) {
+  // Avoids an un-necessary write on read-only fs
+  if (currentContent === content) {
     return
   }
-
   await fs.writeFile(appTypeDeclarations, content)
 }

test/unit/write-app-declarations.test.ts

@@ -0,0 +1,80 @@
+/* eslint-env jest */
+import os from 'os'
+import fs from 'fs-extra'
+import { join } from 'path'
+import { writeAppTypeDeclarations } from 'next/dist/lib/typescript/writeAppTypeDeclarations'
+
+const fixtureDir = join(__dirname, 'fixtures/app-declarations')
+const declarationFile = join(fixtureDir, 'next-env.d.ts')
+const imageImportsEnabled = false
+
+describe('find config', () => {
+  afterEach(() => fs.remove(declarationFile))
+
+  it('should preserve CRLF EOL', async () => {
+    const eol = '\r\n'
+    const content =
+      '/// <reference types="next" />' +
+      eol +
+      '/// <reference types="next/types/global" />' +
+      eol +
+      (imageImportsEnabled
+        ? '/// <reference types="next/image-types/global" />' + eol
+        : '') +
+      eol +
+      '// NOTE: This file should not be edited' +
+      eol +
+      '// see https://nextjs.org/docs/basic-features/typescript for more information.' +
+      eol
+
+    await fs.ensureDir(fixtureDir)
+    await fs.writeFile(declarationFile, content)
+
+    await writeAppTypeDeclarations(fixtureDir, imageImportsEnabled)
+    expect(await fs.readFile(declarationFile, 'utf8')).toBe(content)
+  })
+
+  it('should preserve LF EOL', async () => {
+    const eol = '\n'
+    const content =
+      '/// <reference types="next" />' +
+      eol +
+      '/// <reference types="next/types/global" />' +
+      eol +
+      (imageImportsEnabled
+        ? '/// <reference types="next/image-types/global" />' + eol
+        : '') +
+      eol +
+      '// NOTE: This file should not be edited' +
+      eol +
+      '// see https://nextjs.org/docs/basic-features/typescript for more information.' +
+      eol
+
+    await fs.ensureDir(fixtureDir)
+    await fs.writeFile(declarationFile, content)
+
+    await writeAppTypeDeclarations(fixtureDir, imageImportsEnabled)
+    expect(await fs.readFile(declarationFile, 'utf8')).toBe(content)
+  })
+
+  it('should use OS EOL by default', async () => {
+    const eol = os.EOL
+    const content =
+      '/// <reference types="next" />' +
+      eol +
+      '/// <reference types="next/types/global" />' +
+      eol +
+      (imageImportsEnabled
+        ? '/// <reference types="next/image-types/global" />' + eol
+        : '') +
+      eol +
+      '// NOTE: This file should not be edited' +
+      eol +
+      '// see https://nextjs.org/docs/basic-features/typescript for more information.' +
+      eol
+
+    await fs.ensureDir(fixtureDir)
+    await writeAppTypeDeclarations(fixtureDir, imageImportsEnabled)
+    expect(await fs.readFile(declarationFile, 'utf8')).toBe(content)
+  })
+})