Fix concat

src/Neo.Compiler.MSIL/MSIL/Conv_Multi.cs

@@ -1,3 +1,4 @@
+using Mono.Cecil;
 using Neo.SmartContract;
 using System;
 using System.Collections.Generic;
@@ -645,7 +646,18 @@ private int ConvertCall(OpCode src, NeoMethod to)
                 else if (src.tokenMethod.Contains("::Concat("))
                 {
                     //"System.String System.String::Concat(System.String,System.String)"
-                    Convert1by1(VM.OpCode.CAT, src, to);
+                    if (src.tokenUnknown is MethodReference mref)
+                    {
+                        //Concat can have more than two arguments
+                        for (int x = 0; x < mref.Parameters.Count - 1; x++)
+                        {
+                            Convert1by1(VM.OpCode.CAT, src, to);
+                        }
+                    }
+                    else
+                    {
+                        Convert1by1(VM.OpCode.CAT, src, to);
+                    }
                     Insert1(VM.OpCode.CONVERT, "", to, new byte[] { (byte)VM.Types.StackItemType.ByteString });
                     return 0;
                 }

tests/Neo.Compiler.MSIL.UnitTests/TestClasses/Contract_Concat.cs

@@ -0,0 +1,22 @@
+using Neo.SmartContract.Framework;
+
+namespace Neo.Compiler.MSIL.UnitTests.TestClasses
+{
+    public class Contract_Concat : SmartContract.Framework.SmartContract
+    {
+        public static string TestStringAdd1(string a)
+        {
+            return a + "hello";
+        }
+
+        public static string TestStringAdd2(string a, string b)
+        {
+            return a + b + "hello";
+        }
+
+        public static string TestStringAdd3(string a, string b, string c)
+        {
+            return a + b + c + "hello";
+        }
+    }
+}

tests/Neo.Compiler.MSIL.UnitTests/UnitTest_Concat.cs

@@ -0,0 +1,47 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Neo.Compiler.MSIL.UnitTests.Utils;
+using Neo.VM;
+using Neo.VM.Types;
+
+namespace Neo.Compiler.MSIL.UnitTests
+{
+    [TestClass]
+    public class UnitTest_Concat
+    {
+        private TestEngine _engine;
+
+        [TestInitialize]
+        public void Init()
+        {
+            _engine = new TestEngine();
+            _engine.AddEntryScript("./TestClasses/Contract_Concat.cs");
+        }
+
+        [TestMethod]
+        public void TestStringAdd1()
+        {
+            _engine.Reset();
+            var result = _engine.GetMethod("testStringAdd1").Run("a").ConvertTo(StackItemType.ByteString);
+            Assert.AreEqual(VMState.HALT, _engine.State);
+            Assert.AreEqual("ahello", result.GetString());
+        }
+
+        [TestMethod]
+        public void TestStringAdd2()
+        {
+            _engine.Reset();
+            var result = _engine.GetMethod("testStringAdd2").Run("a", "b").ConvertTo(StackItemType.ByteString);
+            Assert.AreEqual(VMState.HALT, _engine.State);
+            Assert.AreEqual("abhello", result.GetString());
+        }
+
+        [TestMethod]
+        public void TestStringAdd3()
+        {
+            _engine.Reset();
+            var result = _engine.GetMethod("testStringAdd3").Run("a", "b", "c").ConvertTo(StackItemType.ByteString);
+            Assert.AreEqual(VMState.HALT, _engine.State);
+            Assert.AreEqual("abchello", result.GetString());
+        }
+    }
+}