Fix #282: (T)(object)DateTime.Now; decompiles as (T)DateTime.Now;, which does not compile

ICSharpCode.Decompiler/Ast/AstMethodBodyBuilder.cs

@@ -543,12 +543,15 @@ namespace ICSharpCode.Decompiler.Ast
 						}
 						return arg1;
 					}
-				case ILCode.Castclass:
-					return arg1.CastTo(operandAsTypeRef);
 				case ILCode.Unbox_Any:
 					// unboxing does not require a cast if the argument was an isinst instruction
 					if (arg1 is AsExpression && byteCode.Arguments[0].Code == ILCode.Isinst && TypeAnalysis.IsSameType(operand as TypeReference, byteCode.Arguments[0].Operand as TypeReference))
 						return arg1;
+					else
+						goto case ILCode.Castclass;
+				case ILCode.Castclass:
+					if (byteCode.Arguments[0].InferredType.IsGenericParameter)
+						return arg1.CastTo(new PrimitiveType("object")).CastTo(operandAsTypeRef);
 					else
 						return arg1.CastTo(operandAsTypeRef);
 				case ILCode.Isinst:

ICSharpCode.Decompiler/Tests/Generics.cs

@@ -107,4 +107,44 @@ public static class Generics
 		// Tests references to inner classes in generic classes
 		return d.Keys.GetEnumerator();
 	}
+	
+	public static bool IsString<T>(T input)
+	{
+		return input is string;
+	}
+	
+	public static string AsString<T>(T input)
+	{
+		return input as string;
+	}
+	
+	public static string CastToString<T>(T input)
+	{
+		return (string)((object)input);
+	}
+	
+	public static bool IsInt<T>(T input)
+	{
+		return input is int;
+	}
+	
+	public static int CastToInt<T>(T input)
+	{
+		return (int)((object)input);
+	}
+	
+	public static bool IsNullableInt<T>(T input)
+	{
+		return input is int?;
+	}
+	
+	public static int? AsNullableInt<T>(T input)
+	{
+		return input as int?;
+	}
+	
+	public static int? CastToNullableInt<T>(T input)
+	{
+		return (int?)((object)input);
+	}
 }