From 571c28494711a6d0cbe37a32f5fd827f123b8a1e Mon Sep 17 00:00:00 2001
From: Yusuke Wada <yusuke@kamawada.com>
Date: Mon, 1 Jan 2024 18:23:12 +0900
Subject: [PATCH] fix(types): `JSONParsed` supports interface and `Date` etc.
 (#1853)

* fix(types): `JSONParsed` supports interface and `Date` etc.

* denoify

* supports bigint as never

* denoify
---
 deno_dist/utils/types.ts | 15 +++++++--
 src/utils/types.test.ts  | 71 ++++++++++++++++++++++++++++++++++++++++
 src/utils/types.ts       | 15 +++++++--
 3 files changed, 95 insertions(+), 6 deletions(-)
 create mode 100644 src/utils/types.test.ts

diff --git a/deno_dist/utils/types.ts b/deno_dist/utils/types.ts
index 5f4bce2037..0da3742a1b 100644
--- a/deno_dist/utils/types.ts
+++ b/deno_dist/utils/types.ts
@@ -27,9 +27,18 @@ export type JSONPrimitive = string | boolean | number | null | undefined
 export type JSONArray = (JSONPrimitive | JSONObject | JSONArray)[]
 export type JSONObject = { [key: string]: JSONPrimitive | JSONArray | JSONObject | object }
 export type JSONValue = JSONObject | JSONArray | JSONPrimitive
-export type JSONParsed<T> = {
-  [k in keyof T]: T[k] extends JSONValue ? T[k] : string
-}
+// Non-JSON values such as `Date` implement `.toJSON()`, so they can be transformed to a value assignable to `JSONObject`:
+export type JSONParsed<T> = T extends { toJSON(): infer J }
+  ? (() => J) extends () => JSONObject
+    ? J
+    : JSONParsed<J>
+  : T extends JSONPrimitive
+  ? T
+  : T extends Array<infer U>
+  ? Array<JSONParsed<U>>
+  : T extends object
+  ? { [K in keyof T]: JSONParsed<T[K]> }
+  : never
 
 export type InterfaceToType<T> = T extends Function ? T : { [K in keyof T]: InterfaceToType<T[K]> }
 
diff --git a/src/utils/types.test.ts b/src/utils/types.test.ts
new file mode 100644
index 0000000000..4f465149f6
--- /dev/null
+++ b/src/utils/types.test.ts
@@ -0,0 +1,71 @@
+import type { Equal, Expect, JSONParsed } from './types'
+
+describe('JSONParsed', () => {
+  enum SampleEnum {
+    Value1 = 'value1',
+    Value2 = 'value2',
+  }
+
+  interface Meta {
+    metadata: {
+      href: string
+      sampleEnum: SampleEnum
+    }
+  }
+
+  interface SampleInterface {
+    someMeta: Meta
+  }
+
+  type SampleType = {
+    someMeta: Meta
+  }
+
+  it('Should parse a complex type', () => {
+    const sample: JSONParsed<SampleType> = {
+      someMeta: {
+        metadata: {
+          href: '',
+          sampleEnum: SampleEnum.Value1,
+        },
+      },
+    }
+    expectTypeOf(sample).toEqualTypeOf<SampleType>()
+  })
+
+  it('Should parse a complex interface', () => {
+    const sample: JSONParsed<SampleInterface> = {
+      someMeta: {
+        metadata: {
+          href: '',
+          sampleEnum: SampleEnum.Value1,
+        },
+      },
+    }
+    expectTypeOf(sample).toEqualTypeOf<SampleInterface>()
+  })
+
+  it('Should convert Date to string', () => {
+    type Post = {
+      datetime: Date
+    }
+    type Expected = {
+      datetime: string
+    }
+    type Actual = JSONParsed<Post>
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    type verify = Expect<Equal<Expected, Actual>>
+  })
+
+  it('Should convert bigint to never', () => {
+    type Post = {
+      num: bigint
+    }
+    type Expected = {
+      num: never
+    }
+    type Actual = JSONParsed<Post>
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    type verify = Expect<Equal<Expected, Actual>>
+  })
+})
diff --git a/src/utils/types.ts b/src/utils/types.ts
index 5f4bce2037..0da3742a1b 100644
--- a/src/utils/types.ts
+++ b/src/utils/types.ts
@@ -27,9 +27,18 @@ export type JSONPrimitive = string | boolean | number | null | undefined
 export type JSONArray = (JSONPrimitive | JSONObject | JSONArray)[]
 export type JSONObject = { [key: string]: JSONPrimitive | JSONArray | JSONObject | object }
 export type JSONValue = JSONObject | JSONArray | JSONPrimitive
-export type JSONParsed<T> = {
-  [k in keyof T]: T[k] extends JSONValue ? T[k] : string
-}
+// Non-JSON values such as `Date` implement `.toJSON()`, so they can be transformed to a value assignable to `JSONObject`:
+export type JSONParsed<T> = T extends { toJSON(): infer J }
+  ? (() => J) extends () => JSONObject
+    ? J
+    : JSONParsed<J>
+  : T extends JSONPrimitive
+  ? T
+  : T extends Array<infer U>
+  ? Array<JSONParsed<U>>
+  : T extends object
+  ? { [K in keyof T]: JSONParsed<T[K]> }
+  : never
 
 export type InterfaceToType<T> = T extends Function ? T : { [K in keyof T]: InterfaceToType<T[K]> }