fix configuration defaults

Author: ryan-nauman

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

@@ -223,6 +223,9 @@ export async function writeConfigurationDefaults(
         )
     )
   } else if (hasAppDir && !rawConfig.include.includes(nextAppTypes)) {
+    if (!Array.isArray(userTsConfig.include)) {
+      userTsConfig.include = []
+    }
     userTsConfig.include.push(nextAppTypes)
     suggestedActions.push(
       cyan('include') + ' was updated to add ' + bold(`'${nextAppTypes}'`)
@@ -270,14 +273,13 @@ export async function writeConfigurationDefaults(
       )
     }
 
-    // If `strict` is set to `false` or `strictNullChecks` is set to `false`,
+    // If `strict` is set to `false` and `strictNullChecks` is set to `false`,
     // then set `strictNullChecks` to `true`.
     if (
       hasPagesDir &&
       hasAppDir &&
-      userTsConfig.compilerOptions &&
-      !userTsConfig.compilerOptions.strict &&
-      !('strictNullChecks' in userTsConfig.compilerOptions)
+      !tsOptions.strict &&
+      !('strictNullChecks' in tsOptions)
     ) {
       userTsConfig.compilerOptions.strictNullChecks = true
       suggestedActions.push(

test/unit/write-configuration-defaults.test.ts

@@ -0,0 +1,75 @@
+/* eslint-env jest */
+import os from 'os'
+import fs from 'fs-extra'
+import { join } from 'path'
+import { writeConfigurationDefaults } from 'next/dist/lib/typescript/writeConfigurationDefaults'
+import * as ts from 'typescript'
+
+const fixtureDir = join(__dirname, 'fixtures/config-ts')
+const tsconfigFile = join(fixtureDir, 'tsconfig.json')
+const tsconfigBaseFile = join(fixtureDir, 'tsconfig.base.json')
+
+describe('tsconfig.base.json', () => {
+  beforeEach(async () => {
+    await fs.ensureDir(fixtureDir)
+  })
+  afterEach(async () => {
+    await fs.remove(tsconfigFile)
+    await fs.remove(tsconfigBaseFile)
+  })
+
+  it('should support empty includes when base provides it', async () => {
+    const content = {
+      extends: './tsconfig.base.json',
+    }
+
+    const baseContent = {
+      include: ['**/*.ts', '**/*.tsx'],
+    }
+
+    await fs.writeFile(tsconfigFile, JSON.stringify(content, null, 2))
+    await fs.writeFile(tsconfigBaseFile, JSON.stringify(baseContent, null, 2))
+
+    await expect(
+      writeConfigurationDefaults(ts, tsconfigFile, false, true, '.next', true)
+    ).resolves.not.toThrow()
+  })
+
+  it('should not add strictNullChecks if base provides it', async () => {
+    const content = {
+      extends: './tsconfig.base.json',
+      compilerOptions: {
+        plugins: [
+          {
+            name: 'next',
+          },
+        ],
+      },
+    }
+
+    const baseContent = {
+      compilerOptions: {
+        strictNullChecks: true,
+        strict: true,
+      },
+      include: ['next-env.d.ts', '**/*.ts', '**/*.tsx', '.next/types/**/*.ts'],
+      exclude: ['node_modules'],
+    }
+
+    await fs.writeFile(tsconfigFile, JSON.stringify(content, null, 2))
+    await fs.writeFile(tsconfigBaseFile, JSON.stringify(baseContent, null, 2))
+
+    await writeConfigurationDefaults(
+      ts,
+      tsconfigFile,
+      false,
+      true,
+      '.next',
+      true
+    )
+    const output = await fs.readFile(tsconfigFile, 'utf8')
+    const parsed = JSON.parse(output)
+
+    expect(parsed.compilerOptions.strictNullChecks).toBeUndefined()
+  })
+})