From 448a8fc687cca2bcab2353ea4237f1293706d5e2 Mon Sep 17 00:00:00 2001
From: Yusuke Wada <yusuke@kamawada.com>
Date: Mon, 7 Apr 2025 18:41:04 +0900
Subject: [PATCH] fix(zod-openapi): infer Env correctly if the middleware is
 `[]` (#1106)

* fix(zod-openapi): infer Env correctly if the middleware is `[]`

* add changeset
---
 .changeset/dark-kiwis-check.md           |  5 +++++
 packages/zod-openapi/src/index.test-d.ts | 21 +++++++++++++++++++++
 packages/zod-openapi/src/index.ts        |  2 +-
 packages/zod-openapi/tsconfig.spec.json  | 11 ++++++++---
 4 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/dark-kiwis-check.md

diff --git a/.changeset/dark-kiwis-check.md b/.changeset/dark-kiwis-check.md
new file mode 100644
index 00000000..58b4a664
--- /dev/null
+++ b/.changeset/dark-kiwis-check.md
@@ -0,0 +1,5 @@
+---
+'@hono/zod-openapi': patch
+---
+
+fix: infer Env correctly if the middleware is `[]`
diff --git a/packages/zod-openapi/src/index.test-d.ts b/packages/zod-openapi/src/index.test-d.ts
index 99865105..e0127e9c 100644
--- a/packages/zod-openapi/src/index.test-d.ts
+++ b/packages/zod-openapi/src/index.test-d.ts
@@ -337,4 +337,25 @@ describe('Middleware', () => {
       }
     )
   })
+
+  it('Should infer Env correctly when the middleware is empty', async () => {
+    const app = new OpenAPIHono<{ Variables: { foo: string } }>()
+    app.openapi(
+      createRoute({
+        method: 'get',
+        path: '/books',
+        middleware: [] as const, // empty
+        responses: {
+          200: {
+            description: 'response',
+          },
+        },
+      }),
+      (c) => {
+        const foo = c.get('foo')
+        type verify = Expect<Equal<typeof foo, string>>
+        return c.json({})
+      }
+    )
+  })
 })
diff --git a/packages/zod-openapi/src/index.ts b/packages/zod-openapi/src/index.ts
index f42a2f68..6e477c34 100644
--- a/packages/zod-openapi/src/index.ts
+++ b/packages/zod-openapi/src/index.ts
@@ -305,7 +305,7 @@ export type MiddlewareToHandlerType<M extends MiddlewareHandler<any, any, any>[]
     : never
   : M extends [infer Last]
   ? Last // Return the last remaining handler in the array
-  : never
+  : MiddlewareHandler<Env>
 
 type RouteMiddlewareParams<R extends RouteConfig> = OfHandlerType<
   MiddlewareToHandlerType<AsArray<R['middleware']>>
diff --git a/packages/zod-openapi/tsconfig.spec.json b/packages/zod-openapi/tsconfig.spec.json
index 191c0270..a1c2f484 100644
--- a/packages/zod-openapi/tsconfig.spec.json
+++ b/packages/zod-openapi/tsconfig.spec.json
@@ -2,12 +2,17 @@
   "extends": "../../tsconfig.base.json",
   "compilerOptions": {
     "outDir": "../../dist/out-tsc/packages/zod-openapi",
-    "types": ["vitest/globals"]
+    "types": [
+      "vitest/globals"
+    ]
   },
-  "include": ["**/*.test.ts"],
+  "include": [
+    "**/*.test.ts",
+    "**/*.test-d.ts"
+  ],
   "references": [
     {
       "path": "./tsconfig.build.json"
     }
   ]
-}
+}
\ No newline at end of file