Fix: ActorSystem.Settings did not load config from app.config file (#…

…4331)

* Fix: ActorSystem.Settings did not load config from app.config file

* ActorSystemImpl does not need to check for empty config, it can process empty config

* Move spec to ConfigurationSpec. Ignore test on core target (not supported)

src/core/Akka.Tests/App.config

@@ -21,6 +21,7 @@
               }
             }          
           }
+          nonsense.entry = true
       ]]>
     </hocon>
   </akka>

src/core/Akka.Tests/Configuration/ConfigurationSpec.cs

@@ -5,6 +5,7 @@
 // </copyright>
 //-----------------------------------------------------------------------
 
+using System;
 using System.IO;
 using Akka.Configuration.Hocon;
 using System.Linq;
@@ -80,6 +81,20 @@ public void Deserializes_hocon_configuration_from_net_config_file()
 #endif
         }
 
+        // unit test for bug #4330
+        [Fact]
+        public void Should_load_config_from_app_config_file()
+        {
+#if !CORECLR
+            var system = ActorSystem.Create(Guid.NewGuid().ToString());
+            system.Settings.Config.GetBoolean("nonsense.entry").ShouldBeTrue();
+            system.Terminate();
+#else
+            // Skip this test for Linux targets
+            Output.WriteLine("This test is skipped.");
+#endif
+        }
+
     }
 
 }

src/core/Akka/Actor/ActorSystem.cs

@@ -112,7 +112,7 @@ public static ActorSystem Create(string name, Config config)
         /// <returns>A newly created actor system with the given name.</returns>
         public static ActorSystem Create(string name)
         {
-            return CreateAndStartSystem(name, ConfigurationFactory.Default());
+            return CreateAndStartSystem(name, ConfigurationFactory.Load());
         }
 
         private static ActorSystem CreateAndStartSystem(string name, Config withFallback)

src/core/Akka/Actor/Internal/ActorSystemImpl.cs

@@ -74,7 +74,7 @@ public ActorSystemImpl(string name, Config config)
                     $"Invalid ActorSystem name [{name}], must contain only word characters (i.e. [a-zA-Z0-9] plus non-leading '-')", nameof(name));
 
             // Not checking for empty Config here, default values will be substituted in Settings class constructor (called in ConfigureSettings)
-            if(config.IsNullOrEmpty())
+            if(config is null)
                 throw new ArgumentNullException(nameof(config), $"Cannot create {typeof(ActorSystemImpl)}: Configuration must not be null.");
 
             _name = name;