fix: Ensure non-object data in RPC errors is deserialized correctly (#7638)

## Explanation

As-is the compatibility function `deserializeError` strips out valid
`data` if it isn't an object. Serialized values based on the
`JsonRpcError` class may have `data` that is any JSON value. This PR
fixes the issue by adding an additional case to the deserialization to
account for `data` being a non-object JSON value.

This for example ensures that "execution reverted" errors from the node
have the revert data properly populated.

## Checklist

- [x] I've updated the test suite for new or updated code as appropriate
- [x] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [x] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Ensures `deserializeError` retains non-object JSON `data` for RPC
errors while still merging `cause` appropriately.
> 
> - Add `deserializeData` to merge object `data` with `cause` and pass
through primitive/JSON `data` using `isValidJson`
> - Update `deserializeError` to use `deserializeData`; import
`OptionalDataWithOptionalCause` and `isValidJson`
> - Extend tests to cover primitive `data` case and validated error
message behavior
> - Update `CHANGELOG.md` under Unreleased with the fix
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
6d843cb. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: FrederikBolding

packages/json-rpc-engine/CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Upgrade `@metamask/utils` from `^11.8.1` to `^11.9.0` ([#7511](https://github.com/MetaMask/core/pull/7511))
 
+### Fixed
+
+- Ensure non-object data in RPC errors is deserialized correctly when using JsonRpcEngine compatibility tools ([#7638](https://github.com/MetaMask/core/pull/7638))
+
 ## [10.2.0]
 
 ### Added

packages/json-rpc-engine/src/v2/compatibility-utils.test.ts

@@ -525,5 +525,17 @@ describe('compatibility-utils', () => {
 
       expect(result.message).toBe('Internal JSON-RPC error.');
     });
+
+    it('uses correct data when data is a primitive', () => {
+      const thrownValue = {
+        code: 3,
+        message: 'execution reverted',
+        data: '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',
+      };
+
+      const result = deserializeError(thrownValue) as JsonRpcError<string>;
+
+      expect(result.data).toBe(thrownValue.data);
+    });
   });
 });

packages/json-rpc-engine/src/v2/compatibility-utils.ts

@@ -1,6 +1,7 @@
+import type { OptionalDataWithOptionalCause } from '@metamask/rpc-errors';
 import { getMessageFromCode, JsonRpcError } from '@metamask/rpc-errors';
 import type { Json } from '@metamask/utils';
-import { hasProperty, isObject } from '@metamask/utils';
+import { hasProperty, isObject, isValidJson } from '@metamask/utils';
 // ATTN: We must NOT use 'klona/full' here because it freezes properties on the clone.
 import { klona } from 'klona';
 
@@ -132,6 +133,31 @@ export function propagateToRequest(
     });
 }
 
+/**
+ * Deserialize the error property for a thrown error, merging in the cause where possible.
+ *
+ * @param data - The data from the thrown error.
+ * @param cause - The cause from the thrown error.
+ * @returns The deserialized data.
+ */
+function deserializeData(
+  data: unknown,
+  cause: unknown,
+): OptionalDataWithOptionalCause {
+  // If data is an object, merge with cause.
+  if (isObject(data)) {
+    return { ...data, cause };
+  }
+
+  // If data is a JSON value that's not mergeable.
+  if (isValidJson(data)) {
+    return data;
+  }
+
+  // If data is undefined, only use cause.
+  return { cause };
+}
+
 /**
  * Unserialize an error from a thrown value. Creates a {@link JsonRpcError} if
  * the thrown value is an object with a `code` property. Otherwise, creates a
@@ -177,10 +203,7 @@ export function deserializeError(thrown: unknown): Error | JsonRpcError<Json> {
         // eslint-disable-next-line @typescript-eslint/ban-ts-comment
         // @ts-ignore - Our error type is outdated.
         new Error(message, { cause })
-      : new JsonRpcError(code, message, {
-          ...(isObject(data) ? data : undefined),
-          cause,
-        });
+      : new JsonRpcError(code, message, deserializeData(data, cause));
 
   if (typeof stack === 'string') {
     error.stack = stack;