[CodeAction] JoinStringAction: handle the case when left operand is a BinaryOperatorExpression

ICSharpCode.NRefactory.CSharp/Refactoring/CodeActions/JoinStringAction.cs

@@ -31,10 +31,19 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 	{
 		protected override CodeAction GetAction (RefactoringContext context, BinaryOperatorExpression node)
 		{
-			var left = node.Left as PrimitiveExpression;
+			if (node.Operator != BinaryOperatorType.Add)
+				return null;
+
+			PrimitiveExpression left;
+			var leftBinaryOperatorExpr = node.Left as BinaryOperatorExpression;
+			if (leftBinaryOperatorExpr != null && leftBinaryOperatorExpr.Operator == BinaryOperatorType.Add) {
+				left = leftBinaryOperatorExpr.Right as PrimitiveExpression;
+			} else {
+				left = node.Left as PrimitiveExpression;
+			}
 			var right = node.Right as PrimitiveExpression;
 
-			if (node.Operator != BinaryOperatorType.Add || left == null || right == null ||
+			if (left == null || right == null ||
 				!(left.Value is string) || !(right.Value is string) || !node.OperatorToken.Contains(context.Location))
 				return null;
 

ICSharpCode.NRefactory.Tests/CSharp/CodeActions/JoinStringTests.cs

@@ -37,14 +37,14 @@ namespace ICSharpCode.NRefactory.CSharp.CodeActions
 			Test<JoinStringAction> (@"
 class TestClass
 {
-	string TestMethod ()
+	string TestMethod (string arg)
 	{
 		return " + input + @";
 	}
 }", @"
 class TestClass
 {
-	string TestMethod ()
+	string TestMethod (string arg)
 	{
 		return " + output + @";
 	}
@@ -55,6 +55,7 @@ class TestClass
 		public void TestRegularString ()
 		{
 			Test ("\"a\" $+ \"a\"", "\"aa\"");
+			Test ("arg + \"a\" $+ \"a\"", "arg + \"aa\"");
 		}
 
 		[Test]