From 72a29abaaafc1d7a5769613267b1cbe094da4142 Mon Sep 17 00:00:00 2001
From: arimu1 <19286898+arimu1@users.noreply.github.com>
Date: Thu, 6 Aug 2026 06:23:49 +0700
Subject: [PATCH] fix: support negative array index for set/delete/map (#1077)

Normalize negative array indices before creating the update PathRef so
set, delete, and map resolve $[-n] the same way as read.
---
 .../jsonpath/internal/path/PathToken.java     |  3 ++-
 .../java/com/jayway/jsonpath/WriteTest.java   | 26 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
index 34cf1402b..e338d8bf6 100644
--- a/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
+++ b/json-path/src/main/java/com/jayway/jsonpath/internal/path/PathToken.java
@@ -133,8 +133,9 @@ private static Object readObjectProperty(String property, Object model, Evaluati
 
     protected void handleArrayIndex(int index, String currentPath, Object model, EvaluationContextImpl ctx) {
         String evalPath = Utils.concat(currentPath, "[", String.valueOf(index), "]");
-        PathRef pathRef = ctx.forUpdate() ? PathRef.create(model, index) : PathRef.NO_OP;
+        // Normalize negative indices before creating PathRef so set/delete/map match read (#1077)
         int effectiveIndex = index < 0 ? ctx.jsonProvider().length(model) + index : index;
+        PathRef pathRef = ctx.forUpdate() ? PathRef.create(model, effectiveIndex) : PathRef.NO_OP;
         try {
             Object evalHit = ctx.jsonProvider().getArrayIndex(model, effectiveIndex);
             if (isLeaf()) {
diff --git a/json-path/src/test/java/com/jayway/jsonpath/WriteTest.java b/json-path/src/test/java/com/jayway/jsonpath/WriteTest.java
index 5dfb0e3e4..a5a9862c8 100644
--- a/json-path/src/test/java/com/jayway/jsonpath/WriteTest.java
+++ b/json-path/src/test/java/com/jayway/jsonpath/WriteTest.java
@@ -100,6 +100,32 @@ public void an_array_index_can_be_updated() {
         assertThat(res).isEqualTo("a");
     }
 
+    @Test
+    public void a_negative_array_index_can_be_updated() {
+        // set/delete/map must resolve $[-1] like read (#1077)
+        DocumentContext ctx = parse("[\"a\",\"b\",\"c\"]");
+        assertThat(ctx.<String>read("$[-1]")).isEqualTo("c");
+
+        ctx.set("$[-1]", "z");
+        assertThat(ctx.<List<String>>json()).containsExactly("a", "b", "z");
+        assertThat(ctx.<String>read("$[-1]")).isEqualTo("z");
+    }
+
+    @Test
+    public void a_negative_array_index_can_be_deleted() {
+        DocumentContext ctx = parse("[\"a\",\"b\",\"c\"]");
+        ctx.delete("$[-1]");
+        assertThat(ctx.<List<String>>json()).containsExactly("a", "b");
+    }
+
+    @Test
+    public void a_negative_array_index_can_be_mapped() {
+        DocumentContext ctx = parse("[\"a\",\"b\",\"c\"]");
+        ctx.map("$[-1]", (currentValue, configuration) -> currentValue + "!");
+        assertThat(ctx.<List<String>>json()).containsExactly("a", "b", "c!");
+        assertThat(ctx.<String>read("$[-1]")).isEqualTo("c!");
+    }
+
     @Test
     public void an_array_slice_can_be_updated() {