Stop overriding the user's TS config with defaults during next build

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

@@ -41,8 +41,8 @@ export async function runTypeCheck(
   const requiredConfig = getRequiredConfiguration(ts)
 
   const options = {
-    ...effectiveConfiguration.options,
     ...requiredConfig,
+    ...effectiveConfiguration.options,
     declarationMap: false,
     emitDeclarationOnly: false,
     noEmit: true,

test/integration/tsconfig-verifier/pages/index.tsx

@@ -1,6 +1,6 @@
-// eslint-disable-next-line @typescript-eslint/no-unused-vars
+/* eslint-disable @typescript-eslint/no-unused-vars */
 const blah: boolean = false
-// eslint-disable-next-line @typescript-eslint/no-unused-vars
-const blah2 = import('../value').then((r) => r.default)
+// @ts-expect-error ignore the import issue here caused by https://github.com/microsoft/TypeScript/issues/49083
+const blah2 = import('../value.ts').then((r) => r.default)
 
 export default () => <h3>Hello TypeScript</h3>

test/production/supports-module-resolution-nodenext/pages/index.tsx

@@ -0,0 +1,5 @@
+import helloWorldString from 'pkg/sub-export'
+
+export default function Page() {
+  return <p>{helloWorldString}</p>
+}

test/production/supports-module-resolution-nodenext/pkg/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "pkg",
+  "version": "1.0.0",
+  "type": "module",
+  "exports": {
+    "./sub-export": "./src/some-file.js"
+  }
+}

test/production/supports-module-resolution-nodenext/pkg/src/some-file.d.ts

@@ -0,0 +1,2 @@
+declare const _default: 'Hello, world'
+export default _default

test/production/supports-module-resolution-nodenext/pkg/src/some-file.js

@@ -0,0 +1 @@
+export default 'Hello, world'

test/production/supports-module-resolution-nodenext/supports-moduleresolution-nodenext.test.ts

@@ -0,0 +1,26 @@
+import { createNextDescribe, FileRef } from 'e2e-utils'
+import { join } from 'path'
+
+// regression test suite for https://github.com/vercel/next.js/issues/38854
+createNextDescribe(
+  'Does not override tsconfig moduleResolution field during build',
+  {
+    packageJson: { type: 'module' },
+    files: {
+      'tsconfig.json': new FileRef(join(__dirname, 'tsconfig.json')),
+      pages: new FileRef(join(__dirname, 'pages')),
+      pkg: new FileRef(join(__dirname, 'pkg')),
+    },
+    dependencies: {
+      typescript: 'latest',
+      '@types/react': 'latest',
+      '@types/node': 'latest',
+      pkg: './pkg',
+    },
+  },
+  ({ next }) => {
+    it('boots and renders without throwing an error', async () => {
+      await next.render$('/')
+    })
+  }
+)

test/production/supports-module-resolution-nodenext/tsconfig.json

@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "esModuleInterop": true,
+    "module": "esnext",
+    "jsx": "preserve",
+    "target": "es5",
+    "lib": ["dom", "dom.iterable", "esnext"],
+    "allowJs": true,
+    "skipLibCheck": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "noEmit": true,
+    "incremental": true,
+    "moduleResolution": "nodenext",
+    "resolveJsonModule": true,
+    "isolatedModules": true
+  },
+  "exclude": ["node_modules"],
+  "include": ["next-env.d.ts", "components", "pages"]
+}