feat(nuxt): support app config for server routes (#19489)

docs/2.guide/2.directory-structure/3.app-config.md

@@ -38,7 +38,8 @@ export default defineAppConfig({
 When adding `theme` to the `app.config`, Nuxt uses Vite or webpack to bundle the code. We can universally access `theme` both when server-rendering the page and in the browser using [useAppConfig](/docs/api/composables/use-app-config) composable.
 
 ::alert{type=info}
-Support for accessing `useAppConfig()` in Nitro and `server` directory is [coming soon](https://github.com/nuxt/nuxt/issues/14670).
+<!-- TODO: Remove banner when releasing Nuxt on stable channel -->
+Support for accessing `useAppConfig()` in Nitro and `server` directory is [coming soon](https://github.com/nuxt/nuxt/pull/19489) and available on [edge-channel](https://nuxt.com/docs/guide/going-further/edge-channel).
 ::
 
 ```js

packages/nuxt/src/core/nitro.ts

@@ -47,6 +47,13 @@ export async function initNitro (nuxt: Nuxt & { _nitro?: Nitro }) {
           as: '__publicAssetsURL',
           name: 'publicAssetsURL',
           from: resolve(distDir, 'core/runtime/nitro/paths')
+        },
+        {
+          // TODO: Remove after https://github.com/unjs/nitro/issues/1049
+          as: 'defineAppConfig',
+          name: 'defineAppConfig',
+          from: resolve(distDir, 'core/runtime/nitro/config'),
+          priority: -1
         }
       ],
       exclude: [...excludePattern, /[\\/]\.git[\\/]/]
@@ -79,6 +86,10 @@ export async function initNitro (nuxt: Nuxt & { _nitro?: Nitro }) {
         ...nuxt.options.runtimeConfig.nitro
       }
     },
+    appConfig: nuxt.options.appConfig,
+    appConfigFiles: nuxt.options._layers.map(
+      layer => resolve(layer.config.srcDir, 'app.config')
+    ),
     typescript: {
       generateTsConfig: false
     },

packages/nuxt/src/core/runtime/nitro/config.ts

@@ -0,0 +1 @@
+export const defineAppConfig = (config: any) => config

test/basic.test.ts

@@ -1035,6 +1035,9 @@ describe('app config', () => {
     }
 
     expect(html).toContain(JSON.stringify(expectedAppConfig))
+
+    const serverAppConfig = await $fetch('/api/app-config')
+    expect(serverAppConfig).toMatchObject({ appConfig: expectedAppConfig })
   })
 })
 

test/fixtures/basic/server/api/app-config.ts

@@ -0,0 +1,6 @@
+export default defineEventHandler(() => {
+  const appConfig = useAppConfig()
+  return {
+    appConfig
+  }
+})