From badf25dacadcd82b718dae9694b8ff78f7298414 Mon Sep 17 00:00:00 2001
From: Maarten Zuidhoorn <maarten@zuidhoorn.com>
Date: Tue, 10 Dec 2024 13:07:33 +0100
Subject: [PATCH 1/3] Improve error message for invalid JSON values

---
 src/json.ts | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/json.ts b/src/json.ts
index 159ce5e37..29f492729 100644
--- a/src/json.ts
+++ b/src/json.ts
@@ -16,6 +16,8 @@ import {
   union,
   unknown,
   Struct,
+  assert,
+  refine,
 } from '@metamask/superstruct';
 import type {
   Context,
@@ -215,18 +217,20 @@ export const UnsafeJsonStruct: Struct<Json> = define('JSON', (json) =>
  * This struct sanitizes the value before validating it, so that it is safe to
  * use with untrusted input.
  */
-export const JsonStruct = coerce(UnsafeJsonStruct, any(), (value) => {
-  assertStruct(value, UnsafeJsonStruct);
-  return JSON.parse(
-    JSON.stringify(value, (propKey, propValue) => {
-      // Strip __proto__ and constructor properties to prevent prototype pollution.
-      if (propKey === '__proto__' || propKey === 'constructor') {
-        return undefined;
-      }
-      return propValue;
-    }),
-  );
-});
+export const JsonStruct = coerce(
+  UnsafeJsonStruct,
+  refine(any(), 'JSON', (value) => is(value, UnsafeJsonStruct)),
+  (value) =>
+    JSON.parse(
+      JSON.stringify(value, (propKey, propValue) => {
+        // Strip __proto__ and constructor properties to prevent prototype pollution.
+        if (propKey === '__proto__' || propKey === 'constructor') {
+          return undefined;
+        }
+        return propValue;
+      }),
+    ),
+);
 
 /**
  * Check if the given value is a valid {@link Json} value, i.e., a value that is

From 1943d742be4ad90c94a231e7bbc11e6450772fc8 Mon Sep 17 00:00:00 2001
From: Maarten Zuidhoorn <maarten@zuidhoorn.com>
Date: Tue, 10 Dec 2024 13:13:49 +0100
Subject: [PATCH 2/3] Remove unused import

---
 src/json.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/json.ts b/src/json.ts
index 29f492729..0182a332b 100644
--- a/src/json.ts
+++ b/src/json.ts
@@ -16,7 +16,6 @@ import {
   union,
   unknown,
   Struct,
-  assert,
   refine,
 } from '@metamask/superstruct';
 import type {

From c70a520523f0f87c046488bd193f43f4ebd4eb98 Mon Sep 17 00:00:00 2001
From: Maarten Zuidhoorn <maarten@zuidhoorn.com>
Date: Tue, 10 Dec 2024 13:26:28 +0100
Subject: [PATCH 3/3] Add test

---
 src/json.test.ts | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/src/json.test.ts b/src/json.test.ts
index c4e620a58..96c16bec8 100644
--- a/src/json.test.ts
+++ b/src/json.test.ts
@@ -239,6 +239,18 @@ describe('json', () => {
         'Expected a value of type `JSON`, but received: `undefined`',
       );
     });
+
+    it('returns a readable error message for a nested JsonStruct', () => {
+      const struct = object({
+        value: JsonStruct,
+      });
+
+      const [error] = validate({ value: undefined }, struct);
+      assert(error !== undefined);
+      expect(error.message).toBe(
+        'At path: value -- Expected a value of type `JSON`, but received: `undefined`',
+      );
+    });
   });
 
   describe('getSafeJson', () => {