feat(nitro): automatically type middleware/api routes (#708)

src/build.ts

@@ -1,4 +1,4 @@
-import { resolve, join } from 'pathe'
+import { relative, resolve, join } from 'pathe'
 import consola from 'consola'
 import { rollup, watch as rollupWatch } from 'rollup'
 import fse from 'fs-extra'
@@ -55,9 +55,38 @@ export async function build (nitroContext: NitroContext) {
 
   nitroContext.rollupConfig = getRollupConfig(nitroContext)
   await nitroContext._internal.hooks.callHook('nitro:rollup:before', nitroContext)
+  await writeTypes(nitroContext)
   return nitroContext._nuxt.dev ? _watch(nitroContext) : _build(nitroContext)
 }
 
+async function writeTypes (nitroContext: NitroContext) {
+  const routeTypes: Record<string, string[]> = {}
+
+  const middleware = [
+    ...nitroContext.scannedMiddleware,
+    ...nitroContext.middleware
+  ]
+
+  for (const mw of middleware) {
+    if (typeof mw.handle !== 'string') { continue }
+    const relativePath = relative(nitroContext._nuxt.buildDir, mw.handle).replace(/\.[a-z]+$/, '')
+    routeTypes[mw.route] = routeTypes[mw.route] || []
+    routeTypes[mw.route].push(`ReturnType<typeof import('${relativePath}').default>`)
+  }
+
+  const lines = [
+    'declare module \'@nuxt/nitro\' {',
+    '  interface InternalApi {',
+    ...Object.entries(routeTypes).map(([path, types]) => `    '${path}': ${types.join(' | ')}`),
+    '  }',
+    '}',
+    // Makes this a module for augmentation purposes
+    'export {}'
+  ]
+
+  await writeFile(join(nitroContext._nuxt.buildDir, 'nitro.d.ts'), lines.join('\n'))
+}
+
 async function _build (nitroContext: NitroContext) {
   nitroContext.scannedMiddleware = await scanMiddleware(nitroContext._nuxt.serverDir)
 
@@ -117,6 +146,7 @@ async function _watch (nitroContext: NitroContext) {
       nitroContext.scannedMiddleware = middleware
       if (['add', 'addDir'].includes(event)) {
         watcher.close()
+        writeTypes(nitroContext).catch(console.error)
         watcher = startRollupWatcher(nitroContext)
       }
     }

src/types/fetch.d.ts

@@ -0,0 +1,41 @@
+import type { FetchRequest, FetchOptions, FetchResponse } from 'ohmyfetch'
+
+// An interface to extend in a local project
+export declare interface InternalApi { }
+
+export declare type ValueOf<C> = C extends Record<any, any> ? C[keyof C] : never
+
+export declare type MatchedRoutes<Route extends string> = ValueOf<{
+  // exact match, prefix match or root middleware
+  [key in keyof InternalApi]: Route extends key | `${key}/${string}` | '/' ? key : never
+}>
+
+export declare type MiddlewareOf<Route extends string> = Exclude<InternalApi[MatchedRoutes<Route>], Error | void>
+
+export declare type TypedInternalResponse<Route, Default> =
+  Default extends string | boolean | number | null | void | object
+    // Allow user overrides
+    ? Default
+    : Route extends string
+      ? MiddlewareOf<Route> extends never
+        // Bail if only types are Error or void (for example, from middleware)
+        ? Default
+        : MiddlewareOf<Route>
+      : Default
+
+export declare interface $Fetch {
+  <T = unknown, R extends FetchRequest = FetchRequest> (request: R, opts?: FetchOptions): Promise<TypedInternalResponse<R, T>>
+  raw<T = unknown, R extends FetchRequest = FetchRequest> (request: R, opts?: FetchOptions): Promise<FetchResponse<TypedInternalResponse<R, T>>>
+}
+
+declare global {
+  // eslint-disable-next-line no-var
+  var $fetch: $Fetch
+  namespace NodeJS {
+    interface Global {
+      $fetch: $Fetch
+    }
+  }
+}
+
+export default {}

src/types/index.d.ts

@@ -7,4 +7,5 @@ declare module '@nuxt/kit' {
   }
 }
 
+export * from './fetch'
 export * from '../dist'

src/types/shims.d.ts

@@ -1,15 +1,3 @@
-declare global {
-  import type { $Fetch } from 'ohmyfetch'
-
-  // eslint-disable-next-line no-var
-  var $fetch: $Fetch
-  namespace NodeJS {
-    interface Global {
-      $fetch: $Fetch
-    }
-  }
-}
-
 declare module '#storage' {
   import type { Storage } from 'unstorage'
   export const storage: Storage
@@ -21,5 +9,3 @@ declare module '#assets' {
   export function statAsset(id: string): Promise<AssetMeta>
   export function getKeys() : Promise<string[]>
 }
-
-export default {}