fix(nuxt): provide fallback values for undefined runtime config (#18586)

packages/schema/src/config/common.ts

@@ -423,14 +423,17 @@ export default defineUntypedSchema({
    * @type {typeof import('../src/types/config').RuntimeConfig}
    */
   runtimeConfig: {
-    $resolve: async (val: RuntimeConfig, get) => defu(val, {
-      public: {},
-      app: {
-        baseURL: (await get('app')).baseURL,
-        buildAssetsDir: (await get('app')).buildAssetsDir,
-        cdnURL: (await get('app')).cdnURL,
-      }
-    })
+    $resolve: async (val: RuntimeConfig, get) => {
+      provideFallbackValues(val)
+      return defu(val, {
+        public: {},
+        app: {
+          baseURL: (await get('app')).baseURL,
+          buildAssetsDir: (await get('app')).buildAssetsDir,
+          cdnURL: (await get('app')).cdnURL,
+        }
+      })
+    }
   },
 
   /**
@@ -445,3 +448,13 @@ export default defineUntypedSchema({
 
   $schema: {}
 })
+
+function provideFallbackValues (obj: Record<string, any>) {
+  for (const key in obj) {
+    if (typeof obj[key] === 'undefined' || obj[key] === null) {
+      obj[key] = ''
+    } else if (typeof obj[key] === 'object') {
+      provideFallbackValues(obj[key])
+    }
+  }
+}

test/basic.test.ts

@@ -52,6 +52,7 @@ describe('pages', () => {
     expect(html).toContain('Hello Nuxt 3!')
     // should inject runtime config
     expect(html).toContain('RuntimeConfig | testConfig: 123')
+    expect(html).toContain('needsFallback:')
     // composables auto import
     expect(html).toContain('Composable | foo: auto imported from ~/components/foo.ts')
     expect(html).toContain('Composable | bar: auto imported from ~/components/useBar.ts')

test/fixtures/basic/nuxt.config.ts

@@ -51,6 +51,7 @@ export default defineNuxtConfig({
   runtimeConfig: {
     privateConfig: 'secret_key',
     public: {
+      needsFallback: undefined,
       testConfig: 123
     }
   },