From 6836552e2573b833f3375b1a781625897688d1c2 Mon Sep 17 00:00:00 2001
From: Tony Liao <tonyliaoss@google.com>
Date: Tue, 25 Aug 2026 10:48:17 -0700
Subject: [PATCH] Allow later enum aliases to overwrite in C# custom JSON enum
 mapping.

When constructing the custom JSON enum name map in C# JsonParser, remove the
ContainsKey check so that subsequent aliased enum values overwrite earlier ones,
aligning with the "last match wins" semantics used across C++, Java, PHP, and Python.

PiperOrigin-RevId: 970656172
---
 csharp/src/Google.Protobuf/JsonParser.cs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/csharp/src/Google.Protobuf/JsonParser.cs b/csharp/src/Google.Protobuf/JsonParser.cs
index 6db3b8e072..ef9de22820 100644
--- a/csharp/src/Google.Protobuf/JsonParser.cs
+++ b/csharp/src/Google.Protobuf/JsonParser.cs
@@ -774,8 +774,7 @@ namespace Google.Protobuf
             {
                 var jsonOptions = value.GetOptions()?.GetExtension(
                     Pb.Enumvalue.JsonEnumvalueOptionsExtensions.Json);
-                if (jsonOptions != null && jsonOptions.HasString &&
-                    !map.ContainsKey(jsonOptions.String))
+                if (jsonOptions != null && jsonOptions.HasString)
                 {
                     map[jsonOptions.String] = value;
                 }