isEqual: false 'circular references' warning for a reference repeated across sibling keys

[savkaoleg]

isEqual reports "There may be circular references" and returns false for deeply-equal objects

Package: rc-util@5.44.4 and @rc-component/util@1.13.0 (both current; identical logic in src/isEqual.ts)

What happens

isEqual returns false for two objects that are deeply equal, and logs Warning: There may be circular references, when one of them holds the same reference in two different keys. Neither object contains a cycle.

import isEqual from 'rc-util/lib/isEqual';

const shared = [];
const a = { errors: shared, warnings: shared }; // one array, two keys
const b = { errors: [], warnings: [] }; // same value, two separate arrays

isEqual(a, b);
// → false
// → console.error: "Warning: There may be circular references"

JSON.stringify(a) === JSON.stringify(b); // → true

The same happens for any repeated reference, not just arrays:

const point = { x: 1 };
isEqual({ a: point, b: point }, { a: { x: 1 }, b: { x: 1 } }); // → false, warns

Why

refSet is meant to detect cycles, but it records every value the walk has ever visited and never removes anything when the walk leaves a branch:

const refSet = new Set<any>();
function deepEqual(a: any, b: any, level = 1): boolean {
  const circular = refSet.has(a);
  warning(!circular, 'Warning: There may be circular references');
  if (circular) {
    return false;
  }
  ...
  refSet.add(a);   // added on the way in, never removed on the way out

A cycle means a value reachable from itself — that is, a value that is its own ancestor along the current path. The set therefore needs to hold the current path, not the whole history. As written, a value legitimately reached twice in two sibling branches is indistinguishable from a cycle: the second visit finds it in the set, warns, and returns false.

Why it matters in practice

rc-field-form shares one empty-array constant between two fields of a field's meta (Field.tsx):

const EMPTY_ERRORS: any[] = [];
...
public errors: string[] = EMPTY_ERRORS;
public warnings: string[] = EMPTY_ERRORS;

Field.triggerMetaEvent then compares the previous meta with the next via isEqual. Once a field has validated, its errors is a fresh [] while another field's meta still carries the shared constant in both keys — so the comparison hits exactly the case above.

The visible result in any antd app is a Warning: There may be circular references in the dev console after a programmatic form.setFieldValue(...), pointing at application code that has no circular data of any kind. The functional effect is milder but real: isEqual returns false for metas that are equal, so onMetaChange fires when nothing changed.

Suggested fix

Track ancestors rather than history — remove the entry once the walk leaves the branch:

     refSet.add(a);
     const newLevel = level + 1;
-    if (Array.isArray(a)) {
-      ...
-    }
-    // other
-    return false;
+    try {
+      if (Array.isArray(a)) {
+        ...
+      }
+      // other
+      return false;
+    } finally {
+      // `a` is an ancestor only while the walk is inside it; a value reached again in a sibling
+      // branch is a repeat, not a cycle.
+      refSet.delete(a);
+    }
   }

A full patch is attached, with cases added to the existing src/test/isEqual.test.ts. Every test already in that file passes unchanged, including should not equal 6, which is the cyclic one. With the change:

case	before	after
one array held in two keys	false, warns	true, silent
one object reused across sibling keys	false, warns	true, silent
a genuine cycle (a.self = a)	false, warns	false, warns
plainly equal / unequal values	unchanged	unchanged

Happy to open the PR if the approach looks right.