fix: Fix max stack errors on cycles.

package.json

@@ -30,7 +30,6 @@
     "src/**/*.{ts,tsx,css,md}": "prettier --write"
   },
   "dependencies": {
-    "fast-deep-equal": "^3.1.3",
     "is-plain-object": "^5.0.0"
   },
   "peerDependencies": {

src/fields/deepEquals.ts

@@ -0,0 +1,40 @@
+/**
+ * Our own `deepEquals` because either `fast-deep-equals` or `dequal` or etc actually
+ * handle cyclic data structures, despite ChatGTP's assertions/hallucinations.
+ *
+ * Ported from https://github.com/KoryNunn/cyclic-deep-equal which is ISC.
+ */
+export function deepEquals(a: any, b: any, visited: Set<any> = new Set()): boolean {
+  const aType = typeof a;
+  if (aType !== typeof b) return false;
+
+  if (a == null || b == null || !(aType === "object" || aType === "function")) {
+    if (aType === "number" && isNaN(a) && isNaN(b)) return true;
+    return a === b;
+  }
+
+  if (Array.isArray(a) !== Array.isArray(b)) return false;
+
+  const aKeys = Object.keys(a),
+    bKeys = Object.keys(b);
+  if (aKeys.length !== bKeys.length) return false;
+
+  let equal = true;
+
+  for (const key of aKeys) {
+    if (!(key in b)) {
+      equal = false;
+      break;
+    }
+    if (a[key] && a[key] instanceof Object) {
+      if (visited.has(a[key])) break;
+      visited.add(a[key]);
+    }
+    if (!deepEquals(a[key], b[key], visited)) {
+      equal = false;
+      break;
+    }
+  }
+
+  return equal;
+}

src/formState.test.tsx

@@ -1688,6 +1688,26 @@ describe("formState", () => {
     expect(a.value).toEqual({ address: { street: "123", city: "nyc" } });
   });
 
+  it("can have child object states with cycles", () => {
+    // Given an author with an address child
+    // And two addresses that are basically identical and both have cycles
+    const address1: AuthorAddress = { city: "city2" };
+    (address1 as any).someCycle = address1;
+    const address2: AuthorAddress = { city: "city2" };
+    (address2 as any).someCycle = address2;
+    const a = createObjectState<AuthorInput>(
+      {
+        id: { type: "value" },
+        address: { type: "value" },
+      },
+      { address: address1 },
+    );
+    // When we change the address
+    a.address.set(address2);
+    // Then it doesn't error on dirty checks
+    expect(a.address.dirty).toBe(false);
+  });
+
   it("provides isNewEntity", () => {
     // Given an author without an id
     const formState = createObjectState(authorWithAddressConfig, {

src/utils.ts

@@ -1,7 +1,7 @@
-import equal from "fast-deep-equal";
 import { isPlainObject } from "is-plain-object";
 import { isObservable, toJS } from "mobx";
 import { ListFieldConfig, ObjectConfig, ObjectFieldConfig, ValueFieldConfig } from "src/config";
+import { deepEquals } from "src/fields/deepEquals";
 import { InputAndMap, QueryAndMap, UseFormStateOpts } from "src/useFormState";
 
 export type Builtin = Date | Function | Uint8Array | string | number | boolean;
@@ -124,16 +124,16 @@ export function isEmpty(value: any): boolean {
  */
 export function areEqual<T>(a?: T, b?: T, strictOrder?: boolean): boolean {
   if (isPlainObject(a)) {
-    return equal(toJS(a), toJS(b));
+    return deepEquals(toJS(a), toJS(b));
   }
   if (hasToJSON(a) || hasToJSON(b)) {
     const a1 = hasToJSON(a) ? a.toJSON() : a;
     const b1 = hasToJSON(b) ? b.toJSON() : b;
-    return equal(a1, b1);
+    return deepEquals(a1, b1);
   }
   if (a && b && a instanceof Array && b instanceof Array) {
     if (strictOrder !== false) {
-      return equal(a, b);
+      return deepEquals(a, b);
     }
     if (a.length !== b.length) return false;
     return a.every((a1) => b.some((b1) => areEqual(a1, b1)));

yarn.lock

@@ -2843,7 +2843,6 @@ __metadata:
     eslint-plugin-jsx-a11y: ^6.4.1
     eslint-plugin-react: ^7.22.0
     eslint-plugin-react-hooks: ^4.2.0
-    fast-deep-equal: ^3.1.3
     husky: ^3.1.0
     is-plain-object: ^5.0.0
     jest: ^29.7.0