Fix duplicate LoggerMessage event ids; add a guard test

src/StackExchange.Redis/LoggerExtensions.cs

@@ -71,6 +71,7 @@ internal static void LogWithThreadPoolStats(this ILogger? log, string message)
     // awkwardly they read. If a name genuinely must change, pin the old one via the attribute's EventName.
     [LoggerMessage(
         Level = LogLevel.Error,
+        EventId = 127,
         Message = "Connection failed: {EndPoint} ({ConnectionType}, {FailureType}): {ErrorMessage}")]
     internal static partial void LogErrorConnectionFailed(this ILogger logger, Exception? exception, EndPointLogValue endPoint, ConnectionType connectionType, ConnectionFailureType failureType, string errorMessage);
 
@@ -768,7 +769,7 @@ internal static void LogWithThreadPoolStats(this ILogger? log, string message)
     // established" arrived under one id on netfx and another on modern TFMs, for no gain to anyone.
     [LoggerMessage(
         Level = LogLevel.Information,
-        EventId = 99,
+        EventId = 126,
         Message = "TLS connection established successfully using protocol: {SslProtocol}, cipher suite: {CipherSuite}")]
     internal static partial void LogInformationTLSConnectionEstablished(this ILogger logger, System.Security.Authentication.SslProtocols sslProtocol, System.Net.Security.TlsCipherSuite cipherSuite);
 #endif
@@ -781,13 +782,13 @@ internal static void LogWithThreadPoolStats(this ILogger? log, string message)
 
     [LoggerMessage(
         Level = LogLevel.Information,
-        EventId = 116,
+        EventId = 124,
         Message = "{Server}: Requesting maintenance notifications ({Mode})")]
     internal static partial void LogInformationRequestingMaintenanceNotifications(this ILogger logger, ServerEndPointLogValue server, MaintenanceNotificationMode mode);
 
     [LoggerMessage(
         Level = LogLevel.Information,
-        EventId = 117,
+        EventId = 125,
         Message = "{Server}: Maintenance notifications accepted")]
     internal static partial void LogInformationMaintenanceNotificationsAccepted(this ILogger logger, ServerEndPointLogValue server);
 

tests/StackExchange.Redis.Tests/LoggerEventIdTests.cs

@@ -0,0 +1,60 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using Microsoft.Extensions.Logging;
+using Xunit;
+
+namespace StackExchange.Redis.Tests;
+
+/// <summary>
+/// Guards the source-generated <see cref="LoggerMessageAttribute"/> events in <c>LoggerExtensions</c>:
+/// every event must carry an explicit <c>EventId</c>, and no two events may share one. Event ids are
+/// what consumers filter and alert on, so a clash silently merges unrelated events downstream; this
+/// has happened when parallel branches both took "the next free number".
+/// </summary>
+public class LoggerEventIdTests(ITestOutputHelper output) : TestBase(output)
+{
+    [Fact]
+    public void EventIdsAreExplicitAndUnique()
+    {
+        var events = (
+            from method in typeof(LoggerExtensions).GetMethods(BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic)
+            let attrib = method.GetCustomAttribute<LoggerMessageAttribute>()
+            where attrib is not null
+            orderby attrib.EventId, method.Name
+            select (Method: method, Attrib: attrib)).ToList();
+
+        Assert.NotEmpty(events); // if reflection stops finding them, the test is vacuous
+
+        var problems = new List<string>();
+
+        // LoggerMessageAttribute.EventId defaults to -1 when not specified; the generator then emits 0,
+        // which is indistinguishable from "unknown" to a consumer
+        foreach (var (method, attrib) in events.Where(e => e.Attrib.EventId < 0))
+        {
+            problems.Add($"{Describe(method)} has no explicit EventId");
+        }
+
+        foreach (var group in events.Where(e => e.Attrib.EventId >= 0).GroupBy(e => e.Attrib.EventId).Where(g => g.Count() > 1))
+        {
+            problems.Add($"EventId {group.Key} is used {group.Count()} times: {string.Join(", ", group.Select(e => Describe(e.Method)))}");
+        }
+
+        int max = events.Max(e => e.Attrib.EventId);
+        Log($"{events.Count} events; highest EventId {max}; next free EventId {max + 1}");
+        foreach (var problem in problems)
+        {
+            Log(problem);
+        }
+
+        Assert.True(problems.Count == 0, string.Join(Environment.NewLine, problems));
+    }
+
+    private static string Describe(MethodInfo method)
+    {
+        // skip the "this ILogger" parameter; show the rest so overloads are distinguishable
+        var args = method.GetParameters().Skip(1).Select(p => p.ParameterType.Name);
+        return $"{method.Name}({string.Join(", ", args)})";
+    }
+}