From 326df1f711c831296cf8853d78f2bdea508ed292 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Mon, 11 May 2026 12:44:57 +0200
Subject: [PATCH] Update the `deepCompare` helper function to handle `Ref`s and
 `Name`s correctly

Note that `Ref`s and `Name`s are cached globally[1], since that helps reduce object creation (a lot) during parsing.
That cache will be cleared after a period of inactivity in the viewer[2], which is why those primitives cannot *safely* be compared with just `===`/`!==` and also (partially) why abstractions such as `RefSet`/`RefSetCache` are necessary.

Currently `deepCompare` doesn't handle `Ref`s and `Name`s correctly, which may lead to future *intermittent* bugs in any code using the `deepCompare` helper function.

---

[1] This applies to `Cmd` as well, however that doesn't matter in the context of this patch.

[2] Currently, and for more than a decade, set to 30 seconds.
---
 src/core/core_utils.js       |  9 +++++++-
 test/unit/core_utils_spec.js | 45 +++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/src/core/core_utils.js b/src/core/core_utils.js
index 56fa0236f..02c9adae6 100644
--- a/src/core/core_utils.js
+++ b/src/core/core_utils.js
@@ -23,7 +23,7 @@ import {
   Util,
   warn,
 } from "../shared/util.js";
-import { Dict, isName, Ref, RefSet } from "./primitives.js";
+import { Dict, isName, isRefsEqual, Name, Ref, RefSet } from "./primitives.js";
 import { BaseStream } from "./base_stream.js";
 
 const PDF_VERSION_REGEXP = /^[1-9]\.\d$/;
@@ -210,6 +210,13 @@ function deepCompare(a, b) {
   if (a === b) {
     return true;
   }
+  if (a instanceof Ref && b instanceof Ref) {
+    return isRefsEqual(a, b);
+  }
+  if (a instanceof Name && b instanceof Name) {
+    return a.name === b.name;
+  }
+
   if (a instanceof Dict && b instanceof Dict) {
     if (a.size !== b.size) {
       return false;
diff --git a/test/unit/core_utils_spec.js b/test/unit/core_utils_spec.js
index 788e70eab..7f60f4ac8 100644
--- a/test/unit/core_utils_spec.js
+++ b/test/unit/core_utils_spec.js
@@ -31,7 +31,12 @@ import {
   toRomanNumerals,
   validateCSSFont,
 } from "../../src/core/core_utils.js";
-import { Dict, Ref } from "../../src/core/primitives.js";
+import {
+  clearPrimitiveCaches,
+  Dict,
+  Name,
+  Ref,
+} from "../../src/core/primitives.js";
 import { XRefMock } from "./test_utils.js";
 
 describe("core_utils", function () {
@@ -498,6 +503,20 @@ describe("core_utils", function () {
       expect(deepCompare(a, b)).toBeTrue();
     });
 
+    it("should return true for Dicts with same Ref values, after clearing cached Refs", function () {
+      const refA = Ref.get(10, 0);
+      clearPrimitiveCaches();
+      const refB = Ref.get(10, 0);
+      // Ensure that Ref-objects are not identical, after clearing the cache.
+      expect(refA).not.toBe(refB);
+
+      const a = new Dict();
+      a.set("Foo", refA);
+      const b = new Dict();
+      b.set("Foo", refB);
+      expect(deepCompare(a, b)).toBeTrue();
+    });
+
     it("should return false for Dicts with different Ref values", function () {
       const a = new Dict();
       a.set("Foo", Ref.get(10, 0));
@@ -555,6 +574,30 @@ describe("core_utils", function () {
     it("should return false for arrays with different values", function () {
       expect(deepCompare([Ref.get(1, 0)], [Ref.get(2, 0)])).toBeFalse();
     });
+
+    it("should return true for equal Names", function () {
+      const name1 = Name.get("name"),
+        name2 = Name.get("name");
+      expect(name1).toBe(name2); // Names are cached.
+
+      expect(deepCompare(name1, name2)).toBeTrue();
+    });
+
+    it("should return false for different Names", function () {
+      const name1 = Name.get("name"),
+        name2 = Name.get("otherName");
+      expect(deepCompare(name1, name2)).toBeFalse();
+    });
+
+    it("should return true for equal Names, after clearing cached Names", function () {
+      const name1 = Name.get("name");
+      clearPrimitiveCaches();
+      const name2 = Name.get("name");
+      // Ensure that Name-objects are not identical, after clearing the cache.
+      expect(name1).not.toBe(name2);
+
+      expect(deepCompare(name1, name2)).toBeTrue();
+    });
   });
 
   describe("getSizeInBytes", function () {