Avoid freezing child properties of unfreezable objects.

src/utilities/common/__tests__/maybeDeepFeeze.ts

@@ -26,4 +26,16 @@ describe('maybeDeepFreeze', () => {
     expect(Object.isFrozen(result)).toBe(true);
     expect(Object.isFrozen(result.oyez)).toBe(false);
   });
+
+  it('should not freeze child properties of unfreezable objects', () => {
+    const result = maybeDeepFreeze({
+      buffer: Object.assign(Buffer.from("oyez"), {
+        doNotFreeze: { please: "thanks" },
+      }),
+    });
+    expect(Object.isFrozen(result)).toBe(true);
+    expect(Object.isFrozen(result.buffer)).toBe(false);
+    expect(Object.isFrozen(result.buffer.doNotFreeze)).toBe(false);
+    expect(result.buffer.doNotFreeze).toEqual({ please: "thanks" });
+  });
 });

src/utilities/common/maybeDeepFreeze.ts

@@ -4,8 +4,7 @@ import { isNonNullObject } from './objects';
 function deepFreeze(value: any) {
   const workSet = new Set([value]);
   workSet.forEach(obj => {
-    if (isNonNullObject(obj)) {
-      shallowFreeze(obj);
+    if (isNonNullObject(obj) && shallowFreeze(obj) === obj) {
       Object.getOwnPropertyNames(obj).forEach(name => {
         if (isNonNullObject(obj[name])) workSet.add(obj[name]);
       });
@@ -14,15 +13,15 @@ function deepFreeze(value: any) {
   return value;
 }
 
-function shallowFreeze<T extends object>(obj: T): T {
+function shallowFreeze<T extends object>(obj: T): T | null {
   if (__DEV__ && !Object.isFrozen(obj)) {
     try {
       Object.freeze(obj);
     } catch (e) {
       // Some types like Uint8Array and Node.js's Buffer cannot be frozen, but
       // they all throw a TypeError when you try, so we re-throw any exceptions
       // that are not TypeErrors, since that would be unexpected.
-      if (e instanceof TypeError) return obj;
+      if (e instanceof TypeError) return null;
       throw e;
     }
   }