Switched to as cast in Init because some caller do not have the file map at the start of the param list (refsrc System.Web) (dotnet/corefx#30548)

Commit migrated from 331f135dc4

src/libraries/System.Configuration.ConfigurationManager/src/Resources/System.Configuration.ConfigurationManager.rd.xml

@@ -5,6 +5,8 @@
        <!--Both types are instantiated using CreateInstance from TypeUtil.CreateInstance -->
        <Type Name="System.Configuration.ClientConfigurationHost" Dynamic="Required All" />
        <Type Name="System.Configuration.ProtectedConfigurationSection" Dynamic="Required All" />
+       <Type Name="System.Configuration.Internal.InternalConfigHost" Dynamic="Required All" />
+       <Type Name="System.Configuration.Internal.InternalConfigConfigurationFactory" Dynamic="Required All" />
     </Assembly>
   </Library>
 </Directives>

src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/ImplicitMachineConfigHost.cs

@@ -23,14 +23,14 @@ namespace System.Configuration
             out string locationConfigPath, IInternalConfigRoot configRoot, params object[] hostInitConfigurationParams)
         {
             // Stash the filemap so we can see if the machine config was explicitly specified
-            _fileMap = (ConfigurationFileMap)hostInitConfigurationParams[0];
+            _fileMap = hostInitConfigurationParams[0] as ConfigurationFileMap;
             base.InitForConfiguration(ref locationSubPath, out configPath, out locationConfigPath, configRoot, hostInitConfigurationParams);
         }
 
         public override void Init(IInternalConfigRoot configRoot, params object[] hostInitParams)
         {
             // Stash the filemap so we can see if the machine config was explicitly specified
-            _fileMap = (ConfigurationFileMap)hostInitParams[0];
+            _fileMap = hostInitParams[0] as ConfigurationFileMap;
             base.Init(configRoot, hostInitParams);
         }
 

src/libraries/System.Configuration.ConfigurationManager/tests/System.Configuration.ConfigurationManager.Tests.csproj

@@ -103,6 +103,7 @@
     <Compile Include="System\Configuration\SmokeTest.cs" />
     <Compile Include="System\Configuration\StringUtilTests.cs" />
     <Compile Include="System\Configuration\TempConfig.cs" />
+    <Compile Include="System\Configuration\TempConfigurationHost.cs" />
     <Compile Include="System\Configuration\TestData.cs" />
     <Compile Include="System\Configuration\StringValidatorTests.cs" />
     <Compile Include="System\Configuration\SubclassTypeValidatorAttributeTests.cs" />

src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/ImplicitMachineConfigTests.cs

@@ -2,7 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Configuration;
+using System.Configuration.Internal;
 using System.IO;
 using Xunit;
 
@@ -61,5 +63,24 @@ namespace System.ConfigurationTests
                 Assert.Null(config.AppSettings);
             }
         }
+
+        [Fact]
+        public void EnsureInitWithDifferentOrderHostParams() 
+        {
+            string assemblyName = PlatformDetection.IsFullFramework ? "System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" : "System.Configuration.ConfigurationManager";
+
+            // InternalConfigFactory allows you to specify your own host / hostInitParams
+            // Ensure ImplictMachineConfigHost can init within this process and not throw an Invalid cast exception 
+            using (var temp = new TempConfig(TestData.EmptyConfig)) 
+            {
+                string typeName = "System.Configuration.Internal.InternalConfigConfigurationFactory, " + assemblyName;
+
+                Type type = Type.GetType(typeName, true);
+                var configFactory = (IInternalConfigConfigurationFactory) Activator.CreateInstance(type, true);
+                var config = configFactory.Create(typeof(TempConfigurationHost), "test", new ConfigurationFileMap(temp.ConfigPath), "test");
+
+                Assert.NotNull(config);
+            }
+        }
     }
 }

src/libraries/System.Configuration.ConfigurationManager/tests/System/Configuration/TempConfigurationHost.cs

@@ -0,0 +1,90 @@
+using System;
+using System.Configuration;
+using System.Configuration.Internal;
+using System.Reflection;
+
+public class TempConfigurationHost : DelegatingConfigHost 
+{
+    private static string s_assemblyName = PlatformDetection.IsFullFramework ? "System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" : "System.Configuration.ConfigurationManager";
+    private static IInternalConfigConfigurationFactory s_configurationFactory;
+    
+    private ConfigurationFileMap _fileMap;
+
+    public TempConfigurationHost() 
+    {
+        Type type = Type.GetType(InternalHostTypeName, true);
+        Host = (IInternalConfigHost) Activator.CreateInstance(type, true);
+    }
+
+    public override void Init(IInternalConfigRoot configRoot, params object[] hostInitParams) 
+    {
+        Host.Init(configRoot, hostInitParams);
+    }
+
+    public override void InitForConfiguration(ref string locationSubPath, out string configPath, out string locationConfigPath,
+                        IInternalConfigRoot configRoot, params object[] hostInitConfigurationParams) 
+    {
+
+        Host.Init(configRoot, hostInitConfigurationParams);
+
+        _fileMap = hostInitConfigurationParams[1] as ConfigurationFileMap;
+        
+        locationSubPath = ConfigurationFactory.NormalizeLocationSubPath(locationSubPath, null);
+        configPath = "MACHINE/EXE";
+        locationConfigPath = locationSubPath;
+    }
+
+    public override bool IsTrustedConfigPath(string configPath) 
+    {
+        return true;
+    }
+
+    public override bool IsLocationApplicable(string configPath) 
+    {
+        return true;
+    }
+
+    public override bool IsFullTrustSectionWithoutAptcaAllowed(IInternalConfigRecord configRecord) 
+    {
+        return true;
+    }
+
+    public override bool PrefetchAll(string configPath, string streamName)
+    {
+        return false;
+    }
+
+    public override bool PrefetchSection(string sectionGroupName, string sectionName)
+    {
+        return false;
+    }
+
+    public override string GetStreamName(string configPath) 
+    {
+        return _fileMap.MachineConfigFilename;
+    }
+
+    static string InternalConfigConfigurationFactoryTypeName 
+    {
+        get { return "System.Configuration.Internal.InternalConfigConfigurationFactory, " + s_assemblyName; }
+    }
+
+    static string InternalHostTypeName 
+    {
+        get { return "System.Configuration.Internal.InternalConfigHost, " + s_assemblyName; }
+    }
+
+    static internal IInternalConfigConfigurationFactory ConfigurationFactory 
+    {
+        get 
+        {    
+            if (s_configurationFactory == null) 
+            {
+                Type type = Type.GetType(InternalConfigConfigurationFactoryTypeName, true);
+                s_configurationFactory = (IInternalConfigConfigurationFactory) Activator.CreateInstance(type, true);
+            }
+
+            return s_configurationFactory;
+        }
+    }
+}