fix(helper/adapter): correct env type (#3885)

* fix(helper/adapter): correct `env` type

* support another pattern and add test

src/helper/adapter/index.test.ts

@@ -16,13 +16,39 @@ describe('env', () => {
         MY_VAR: string
       }
     }
-    const app = new Hono<Env>()
 
-    it('Should set the type of the Context correctly and not throw a type error')
-    app.get('/var', (c) => {
-      const { MY_VAR } = env<{ MY_VAR: string }>(c)
-      return c.json({
-        var: MY_VAR,
+    it('Should not throw type errors with env has generics', () => {
+      const app = new Hono()
+      app.get('/var', (c) => {
+        const { MY_VAR } = env<{ MY_VAR: string }>(c)
+        expectTypeOf<string>(MY_VAR)
+        return c.json({
+          var: MY_VAR,
+        })
+      })
+    })
+
+    it('Should not throw type errors with Hono has generics', () => {
+      const app = new Hono<Env>()
+
+      app.get('/var', (c) => {
+        const { MY_VAR } = env(c)
+        expectTypeOf<string>(MY_VAR)
+        return c.json({
+          var: MY_VAR,
+        })
+      })
+    })
+
+    it('Should not throw type errors with env and Hono have generics', () => {
+      const app = new Hono<Env>()
+
+      app.get('/var', (c) => {
+        const { MY_VAR } = env<{ MY_VAR: string }>(c)
+        expectTypeOf<string>(MY_VAR)
+        return c.json({
+          var: MY_VAR,
+        })
       })
     })
   })

src/helper/adapter/index.ts

@@ -9,13 +9,11 @@ export type Runtime = 'node' | 'deno' | 'bun' | 'workerd' | 'fastly' | 'edge-lig
 
 export const env = <
   T extends Record<string, unknown>,
-  C extends Context = Context<
-    {} & {
-      Bindings: T
-    }
-  >
+  C extends Context = Context<{
+    Bindings: T
+  }>
 >(
-  c: C,
+  c: T extends Record<string, unknown> ? Context : C,
   runtime?: Runtime
 ): T & C['env'] => {
   // eslint-disable-next-line @typescript-eslint/no-explicit-any