From 99d229e186e1e5d08cb1fc417b4b911ade7aef33 Mon Sep 17 00:00:00 2001
From: Moti Zilberman <moti@fb.com>
Date: Wed, 23 Oct 2019 00:55:30 -0700
Subject: [PATCH] Make deepDiffer behavior with function inputs configurable,
 add logging

Summary: Changelog: [Internal]

Reviewed By: yungsters

Differential Revision: D17951644

fbshipit-source-id: 34bff1937a6157b049193359cb0ad346c48287a6
---
 .../differ/__tests__/deepDiffer-test.js       | 52 +++++++++++++++++++
 Libraries/Utilities/differ/deepDiffer.js      | 39 ++++++++++++--
 2 files changed, 86 insertions(+), 5 deletions(-)

diff --git a/Libraries/Utilities/differ/__tests__/deepDiffer-test.js b/Libraries/Utilities/differ/__tests__/deepDiffer-test.js
index 71ae73e59fb..a2aca448f33 100644
--- a/Libraries/Utilities/differ/__tests__/deepDiffer-test.js
+++ b/Libraries/Utilities/differ/__tests__/deepDiffer-test.js
@@ -128,4 +128,56 @@ describe('deepDiffer', function() {
       ),
     ).toBe(false);
   });
+  it('should consider all functions equal', () => {
+    expect(deepDiffer(() => {}, x => x)).toBe(false);
+    const f = () => {};
+    expect(deepDiffer(f, f)).toBe(false);
+  });
+  it('should compare functions if unsafelyIgnoreFunctions is false', () => {
+    expect(
+      deepDiffer(() => {}, x => x, undefined, {unsafelyIgnoreFunctions: false}),
+    ).toBe(true);
+    const f = () => {};
+    expect(deepDiffer(f, f, undefined, {unsafelyIgnoreFunctions: false})).toBe(
+      false,
+    );
+
+    // shorthand, omitting maxDepth
+    expect(deepDiffer(() => {}, x => x, {unsafelyIgnoreFunctions: false})).toBe(
+      true,
+    );
+    expect(deepDiffer(f, f, {unsafelyIgnoreFunctions: false})).toBe(false);
+  });
+  it('should log when implicitly considering two different functions equal', () => {
+    function a() {}
+    function b() {}
+    const listeners = {onDifferentFunctionsIgnored: jest.fn()};
+    deepDiffer.unstable_setLogListeners(listeners);
+    try {
+      deepDiffer(a, a);
+      expect(listeners.onDifferentFunctionsIgnored).not.toHaveBeenCalled();
+
+      deepDiffer(a, b);
+      expect(listeners.onDifferentFunctionsIgnored.mock.calls).toEqual([
+        ['a', 'b'],
+      ]);
+    } finally {
+      deepDiffer.unstable_setLogListeners(null);
+    }
+  });
+  it('should not log when explicitly considering two different functions equal', () => {
+    function a() {}
+    function b() {}
+    const listeners = {onDifferentFunctionsIgnored: jest.fn()};
+    deepDiffer.unstable_setLogListeners(listeners);
+    try {
+      deepDiffer(a, a, {unsafelyIgnoreFunctions: true});
+      expect(listeners.onDifferentFunctionsIgnored).not.toHaveBeenCalled();
+
+      deepDiffer(a, b, {unsafelyIgnoreFunctions: true});
+      expect(listeners.onDifferentFunctionsIgnored).not.toHaveBeenCalled();
+    } finally {
+      deepDiffer.unstable_setLogListeners(null);
+    }
+  });
 });
diff --git a/Libraries/Utilities/differ/deepDiffer.js b/Libraries/Utilities/differ/deepDiffer.js
index cae6cde1d06..ff8bd4628d1 100644
--- a/Libraries/Utilities/differ/deepDiffer.js
+++ b/Libraries/Utilities/differ/deepDiffer.js
@@ -10,14 +10,31 @@
 
 'use strict';
 
+let logListeners;
+
+type LogListeners = {|
+  +onDifferentFunctionsIgnored: (nameOne: ?string, nameTwo: ?string) => void,
+|};
+
+type Options = {|+unsafelyIgnoreFunctions?: boolean|};
+
+function unstable_setLogListeners(listeners: ?LogListeners) {
+  logListeners = listeners;
+}
+
 /*
  * @returns {bool} true if different, false if equal
  */
 const deepDiffer = function(
   one: any,
   two: any,
-  maxDepth: number = -1,
+  maxDepthOrOptions: Options | number = -1,
+  maybeOptions?: Options,
 ): boolean {
+  const options =
+    typeof maxDepthOrOptions === 'number' ? maybeOptions : maxDepthOrOptions;
+  const maxDepth =
+    typeof maxDepthOrOptions === 'number' ? maxDepthOrOptions : -1;
   if (maxDepth === 0) {
     return true;
   }
@@ -26,8 +43,19 @@ const deepDiffer = function(
     return false;
   }
   if (typeof one === 'function' && typeof two === 'function') {
-    // We consider all functions equal
-    return false;
+    // We consider all functions equal unless explicitly configured otherwise
+    let unsafelyIgnoreFunctions = options?.unsafelyIgnoreFunctions;
+    if (unsafelyIgnoreFunctions == null) {
+      if (
+        logListeners &&
+        logListeners.onDifferentFunctionsIgnored &&
+        (!options || !('unsafelyIgnoreFunctions' in options))
+      ) {
+        logListeners.onDifferentFunctionsIgnored(one.name, two.name);
+      }
+      unsafelyIgnoreFunctions = true;
+    }
+    return !unsafelyIgnoreFunctions;
   }
   if (typeof one !== 'object' || one === null) {
     // Primitives can be directly compared
@@ -48,13 +76,13 @@ const deepDiffer = function(
       return true;
     }
     for (let ii = 0; ii < len; ii++) {
-      if (deepDiffer(one[ii], two[ii], maxDepth - 1)) {
+      if (deepDiffer(one[ii], two[ii], maxDepth - 1, options)) {
         return true;
       }
     }
   } else {
     for (const key in one) {
-      if (deepDiffer(one[key], two[key], maxDepth - 1)) {
+      if (deepDiffer(one[key], two[key], maxDepth - 1, options)) {
         return true;
       }
     }
@@ -70,3 +98,4 @@ const deepDiffer = function(
 };
 
 module.exports = deepDiffer;
+module.exports.unstable_setLogListeners = unstable_setLogListeners;