implement support for op_True and extend unit test

ICSharpCode.Decompiler/Ast/Transforms/ReplaceMethodCallsWithOperators.cs

@@ -50,7 +50,7 @@ namespace ICSharpCode.Decompiler.Ast.Transforms
 			var arguments = invocationExpression.Arguments.ToArray();
 			
 			// Reduce "String.Concat(a, b)" to "a + b"
-			if (methodRef != null && methodRef.Name == "Concat" && methodRef.DeclaringType.FullName == "System.String" && arguments.Length >= 2)
+			if (methodRef.Name == "Concat" && methodRef.DeclaringType.FullName == "System.String" && arguments.Length >= 2)
 			{
 				invocationExpression.Arguments.Clear(); // detach arguments from invocationExpression
 				Expression expr = arguments[0];
@@ -97,7 +97,10 @@ namespace ICSharpCode.Decompiler.Ast.Transforms
 				return null;
 			}
 			if (methodRef.Name == "op_Implicit" && arguments.Length == 1) {
-				arguments[0].Remove(); // detach argument
+				invocationExpression.ReplaceWith(arguments[0]);
+				return null;
+			}
+			if (methodRef.Name == "op_True" && arguments.Length == 1 && invocationExpression.Role == AstNode.Roles.Condition) {
 				invocationExpression.ReplaceWith(arguments[0]);
 				return null;
 			}

ICSharpCode.Decompiler/Tests/CustomShortCircuitOperators.cs

@@ -29,6 +29,11 @@ public static class CustomShortCircuitOperators
 		{
 			return null;
 		}
+		
+		public static bool operator !(CustomShortCircuitOperators.C x)
+		{
+			return false;
+		}
 
 		private static void Main()
 		{
@@ -39,5 +44,32 @@ public static class CustomShortCircuitOperators
 			Console.WriteLine(c3.ToString());
 			Console.WriteLine(c4.ToString());
 		}
+		
+		private static void Test2()
+		{
+			CustomShortCircuitOperators.C c = new CustomShortCircuitOperators.C();
+			if (c && c)
+			{
+				Console.WriteLine(c.ToString());
+			}
+			
+			if (!(c && c))
+			{
+				Console.WriteLine(c.ToString());
+			}
+		}
+		
+		private static void Test3()
+		{
+			CustomShortCircuitOperators.C c = new CustomShortCircuitOperators.C();
+			if (c)
+			{
+				Console.WriteLine(c.ToString());
+			}
+			if (!c)
+			{
+				Console.WriteLine(c.ToString());
+			}
+		}
 	}
 }