Decouple LoggingConfiguration from XmlLoggingConfiguration (#3449)

src/NLog/Config/IInitializeSucceeded.cs

@@ -0,0 +1,43 @@
+// 
+// Copyright (c) 2004-2019 Jaroslaw Kowalski <jaak@jkowalski.net>, Kim Christensen, Julian Verdurmen
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without 
+// modification, are permitted provided that the following conditions 
+// are met:
+// 
+// * Redistributions of source code must retain the above copyright notice, 
+//   this list of conditions and the following disclaimer. 
+// 
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution. 
+// 
+// * Neither the name of Jaroslaw Kowalski nor the names of its 
+//   contributors may be used to endorse or promote products derived from this
+//   software without specific prior written permission. 
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 
+// THE POSSIBILITY OF SUCH DAMAGE.
+// 
+
+namespace NLog.Config
+{
+    internal interface IInitializeSucceeded
+    {
+        /// <summary>
+        /// Did the Initialize Succeeded? <c>true</c>= success, <c>false</c>= error, <c>null</c> = initialize not started yet.
+        /// </summary>
+        bool? InitializeSucceeded { get; }
+    }
+}

src/NLog/Config/LoggingConfiguration.cs

@@ -482,7 +482,7 @@ internal LoggingConfiguration ReloadNewConfig()
                 //problem: XmlLoggingConfiguration.Initialize eats exception with invalid XML. ALso XmlLoggingConfiguration.Reload never returns null.
                 //therefor we check the InitializeSucceeded property.
 
-                if (newConfig is XmlLoggingConfiguration xmlConfig && xmlConfig.InitializeSucceeded != true)
+                if (newConfig is IInitializeSucceeded config2 && config2.InitializeSucceeded != true)
                 {
                     InternalLogger.Warn("NLog Config Reload() failed. Invalid XML?");
                     return null;

src/NLog/Config/XmlLoggingConfiguration.cs

@@ -57,7 +57,7 @@ namespace NLog.Config
     /// - This class is thread-safe.<c>.ToList()</c> is used for that purpose.
     /// - Update TemplateXSD.xml for changes outside targets
     /// </remarks>
-    public class XmlLoggingConfiguration : LoggingConfigurationParser
+    public class XmlLoggingConfiguration : LoggingConfigurationParser, IInitializeSucceeded
     {
 #if __ANDROID__