From 33c2fae0bae6a5e029cb7ca9bb5b4c9e63995c97 Mon Sep 17 00:00:00 2001
From: Brian Smith <brian@dbsoft.org>
Date: Sat, 7 Mar 2026 01:17:18 -0600
Subject: [PATCH] Issue #2304 - Part 4 - Add xray support for the Error cause
 property. https://bugzilla.mozilla.org/show_bug.cgi?id=1679653

---
 js/xpconnect/src/XPCJSContext.cpp     | 1 +
 js/xpconnect/src/xpcprivate.h         | 1 +
 js/xpconnect/wrappers/XrayWrapper.cpp | 5 +++++
 3 files changed, 7 insertions(+)

diff --git a/js/xpconnect/src/XPCJSContext.cpp b/js/xpconnect/src/XPCJSContext.cpp
index 0a5d248185..e93854a9f9 100644
--- a/js/xpconnect/src/XPCJSContext.cpp
+++ b/js/xpconnect/src/XPCJSContext.cpp
@@ -111,6 +111,7 @@ const char* const XPCJSContext::mStrings[] = {
     "columnNumber",         // IDX_COLUMNNUMBER
     "stack",                // IDX_STACK
     "message",              // IDX_MESSAGE
+    "cause",                // IDX_CAUSE
     "errors",               // IDX_ERRORS
     "lastIndex"             // IDX_LASTINDEX
 };
diff --git a/js/xpconnect/src/xpcprivate.h b/js/xpconnect/src/xpcprivate.h
index 087e81a7ba..fc9a254a5c 100644
--- a/js/xpconnect/src/xpcprivate.h
+++ b/js/xpconnect/src/xpcprivate.h
@@ -495,6 +495,7 @@ public:
         IDX_COLUMNNUMBER            ,
         IDX_STACK                   ,
         IDX_MESSAGE                 ,
+        IDX_CAUSE                   ,
         IDX_ERRORS                  ,
         IDX_LASTINDEX               ,
         IDX_TOTAL_COUNT // just a count of the above
diff --git a/js/xpconnect/wrappers/XrayWrapper.cpp b/js/xpconnect/wrappers/XrayWrapper.cpp
index 8fc73b5d09..4660535a1b 100644
--- a/js/xpconnect/wrappers/XrayWrapper.cpp
+++ b/js/xpconnect/wrappers/XrayWrapper.cpp
@@ -609,6 +609,11 @@ JSXrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper,
                 return true;
             }
 
+            // The optional .cause property can have any value.
+            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_CAUSE)) {
+                return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
+            }
+
             if (key == JSProto_AggregateError &&
                 id == GetJSIDByIndex(cx, XPCJSContext::IDX_ERRORS)) {
                 return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);