show config file path in error message

fixes #227

Author: FreeAndNil

src/log4net.Tests/Config/XmlConfiguratorTest.cs

@@ -0,0 +1,60 @@
+#region Apache License
+//
+// Licensed to the Apache Software Foundation (ASF) under one or more 
+// contributor license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership. 
+// The ASF licenses this file to you under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with 
+// the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#endregion
+
+#if NET8_0_OR_GREATER
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Xml;
+using log4net.Config;
+using log4net.Repository;
+using log4net.Util;
+using NUnit.Framework;
+
+namespace log4net.Tests.Config;
+
+/// <summary>
+/// Tests for <see cref="XmlConfigurator"/> class.
+/// </summary>
+[TestFixture]
+public class XmlConfiguratorTest
+{
+  /// <summary>
+  /// Show config file path in error message
+  /// </summary>
+  [Test]
+  public void ConfigureWithUnkownConfigFile()
+  {
+    Func<XmlElement?> getConfigSection = () => null;
+    ILoggerRepository repository = LogManager.CreateRepository(Guid.NewGuid().ToString());
+    SystemInfo.EntryAssemblyLocation = Guid.NewGuid().ToString();
+    List<LogLog> configurationMessages = [];
+
+    using (new LogLog.LogReceivedAdapter(configurationMessages))
+    {
+      typeof(XmlConfigurator)
+        .GetMethod("InternalConfigure", BindingFlags.NonPublic | BindingFlags.Static, [typeof(ILoggerRepository), getConfigSection.GetType()])!
+        .Invoke(null, [repository, getConfigSection]);
+    }
+
+    Assert.That(configurationMessages, Has.Count.EqualTo(1));
+    Assert.That(configurationMessages[0].Message, Contains.Substring(SystemInfo.EntryAssemblyLocation + ".config"));
+  }
+}
+#endif

src/log4net/Config/XmlConfigurator.cs

@@ -66,15 +66,15 @@ public static ICollection Configure(ILoggerRepository repository)
 
     using (new LogLog.LogReceivedAdapter(configurationMessages))
     {
-      InternalConfigure(repository);
+      InternalConfigure(repository, () => System.Configuration.ConfigurationManager.GetSection("log4net") as XmlElement);
     }
 
     repository.ConfigurationMessages = configurationMessages;
 
     return configurationMessages;
   }
 
-  private static void InternalConfigure(ILoggerRepository repository)
+  private static void InternalConfigure(ILoggerRepository repository, Func<XmlElement?> getConfigSection)
   {
     LogLog.Debug(_declaringType, $"configuring repository [{repository.Name}] using .config file section");
 
@@ -90,10 +90,12 @@ private static void InternalConfigure(ILoggerRepository repository)
 
     try
     {
-      if (System.Configuration.ConfigurationManager.GetSection("log4net") is not XmlElement configElement)
+      if (getConfigSection() is not XmlElement configElement)
       {
         // Failed to load the xml config using configuration settings handler
-        LogLog.Error(_declaringType, "Failed to find configuration section 'log4net' in the application's .config file. Check your .config file for the <log4net> and <configSections> elements. The configuration section should look like: <section name=\"log4net\" type=\"log4net.Config.Log4NetConfigurationSectionHandler,log4net\" />");
+        LogLog.Error(_declaringType, @$"Failed to find configuration section 'log4net' in the .config file '{SystemInfo.ConfigurationFileLocation}'.
+Check your .config file for the <log4net> and <configSections> elements.
+The configuration section should look like: <section name=""log4net"" type=""log4net.Config.Log4NetConfigurationSectionHandler,log4net"" />");
       }
       else
       {