From f75d9ed091827cff322f91cf6f0da519a5d6b030 Mon Sep 17 00:00:00 2001
From: Ruben Bridgewater <ruben@bridgewater.de>
Date: Mon, 29 Nov 2021 18:00:26 +0100
Subject: [PATCH] assert,util: compare RegExp.lastIndex while using deep equal
 checks

Compare the `lastIndex` property of regular expressions next to the
flags and source property.

Fixes: https://github.com/nodejs/node/issues/28766

Signed-off-by: Ruben Bridgewater <ruben@bridgewater.de>
---
 doc/api/assert.md                 | 10 ++++++++++
 lib/internal/util/comparisons.js  |  4 +++-
 test/parallel/test-assert-deep.js |  4 ++--
 3 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/doc/api/assert.md b/doc/api/assert.md
index a22a6082c3a379..21966d4d140514 100644
--- a/doc/api/assert.md
+++ b/doc/api/assert.md
@@ -465,6 +465,9 @@ An alias of [`assert.ok()`][].
 <!-- YAML
 added: v0.1.21
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/REPLACEME
+    description: Regular expressions lastIndex property is now compared as well
   - version:
       - v16.0.0
       - v14.18.0
@@ -539,6 +542,8 @@ are also recursively evaluated by the following rules.
   objects.
 * [`Symbol`][] properties are not compared.
 * [`WeakMap`][] and [`WeakSet`][] comparison does not rely on their values.
+* [`RegExp`][] lastIndex, flags and source are always compared, even if these
+  are not enumerable properties.
 
 The following example does not throw an [`AssertionError`][] because the
 primitives are considered equal by the [Abstract Equality Comparison][]
@@ -642,6 +647,9 @@ parameter is an instance of an [`Error`][] then it will be thrown instead of the
 <!-- YAML
 added: v1.2.0
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/REPLACEME
+    description: Regular expressions lastIndex property is now compared as well
   - version: v9.0.0
     pr-url: https://github.com/nodejs/node/pull/15169
     description: Enumerable symbol properties are now compared.
@@ -697,6 +705,8 @@ are recursively evaluated also by the following rules.
   reference.
 * [`WeakMap`][] and [`WeakSet`][] comparison does not rely on their values. See
   below for further details.
+* [`RegExp`][] lastIndex, flags and source are always compared, even if these
+  are not enumerable properties.
 
 ```mjs
 import assert from 'assert/strict';
diff --git a/lib/internal/util/comparisons.js b/lib/internal/util/comparisons.js
index 95515fb78ace0d..c126bd6346dae7 100644
--- a/lib/internal/util/comparisons.js
+++ b/lib/internal/util/comparisons.js
@@ -63,7 +63,9 @@ const kIsMap = 3;
 
 // Check if they have the same source and flags
 function areSimilarRegExps(a, b) {
-  return a.source === b.source && a.flags === b.flags;
+  return a.source === b.source &&
+         a.flags === b.flags &&
+         a.lastIndex === b.lastIndex;
 }
 
 function areSimilarFloatArrays(a, b) {
diff --git a/test/parallel/test-assert-deep.js b/test/parallel/test-assert-deep.js
index bdc634fb5f6ab0..22e01afff15211 100644
--- a/test/parallel/test-assert-deep.js
+++ b/test/parallel/test-assert-deep.js
@@ -712,7 +712,7 @@ assertNotDeepOrStrict(/a/igm, /a/im);
 {
   const re1 = /a/g;
   re1.lastIndex = 3;
-  assert.deepEqual(re1, /a/g);
+  assert.notDeepEqual(re1, /a/g);
 }
 
 assert.deepEqual(4, '4');
@@ -852,7 +852,7 @@ assert.throws(
 {
   const re1 = /a/;
   re1.lastIndex = 3;
-  assert.deepStrictEqual(re1, /a/);
+  assert.notDeepStrictEqual(re1, /a/);
 }
 
 assert.throws(