Use interpolation to cover some more basic xml cases

Author: GrahamTheCoder

CodeConverter/CSharp/ExpressionNodeVisitor.cs

@@ -90,22 +90,36 @@ public override async Task<CSharpSyntaxNode> DefaultVisit(SyntaxNode node)
                 .WithNodeInformation(node);
         }
 
+        public override async Task<CSharpSyntaxNode> VisitXmlEmbeddedExpression(VBSyntax.XmlEmbeddedExpressionSyntax node) =>
+            await node.Expression.AcceptAsync<ExpressionSyntax>(TriviaConvertingExpressionVisitor);
+
         public override async Task<CSharpSyntaxNode> VisitXmlElement(VBasic.Syntax.XmlElementSyntax node)
         {
             _extraUsingDirectives.Add("System.Xml.Linq");
-            var aggregatedContent = node.Content.Select(n => n.ToString()).Aggregate(String.Empty, (a, b) => a + b);
-            var xmlAsString = $"{node.StartTag}{aggregatedContent}{node.EndTag}".Trim();
+            var interpolations = await AcceptXmlInterpolated(node);
+            var interpolationsList = SyntaxFactory.List(interpolations);
+            var xmlAsString = $"{node.StartTag}{interpolationsList}{node.EndTag}".Trim();
+            var interpolatedString = SyntaxFactory.InterpolatedStringExpression(SyntaxFactory.Token(SyntaxKind.InterpolatedStringStartToken), interpolationsList, SyntaxFactory.Token(SyntaxKind.InterpolatedStringEndToken));
             return SyntaxFactory.InvocationExpression(
                     SyntaxFactory.MemberAccessExpression(
                         SyntaxKind.SimpleMemberAccessExpression,
                         SyntaxFactory.IdentifierName("XElement"),
                         SyntaxFactory.IdentifierName("Parse")))
-                .WithArgumentList(
-                    ExpressionSyntaxExtensions.CreateArgList(
-                        SyntaxFactory.LiteralExpression(SyntaxKind.StringLiteralExpression,
-                            SyntaxFactory.Literal(xmlAsString))
-                    )
-                );
+                .WithArgumentList(ExpressionSyntaxExtensions.CreateArgList(interpolatedString));
+        }
+
+        private static InterpolatedStringTextSyntax InterpolatedStringText(string text) =>
+            SyntaxFactory.InterpolatedStringText(SyntaxFactory.Token(SyntaxFactory.TriviaList(), SyntaxKind.InterpolatedStringTextToken, text, text, SyntaxFactory.TriviaList()));
+
+        private async Task<IEnumerable<InterpolatedStringContentSyntax>> AcceptXmlInterpolated(VBSyntax.XmlNodeSyntax n)
+        {
+            if (n is VBSyntax.XmlElementSyntax xmlEs) {
+                return InterpolatedStringText(xmlEs.StartTag.ToString()).Yield()
+                .Concat(await xmlEs.Content.SelectManyAsync(AcceptXmlInterpolated))
+                .Concat(InterpolatedStringText(xmlEs.EndTag.ToString()));
+            }
+            var expression = await n.AcceptAsync<ExpressionSyntax>(TriviaConvertingExpressionVisitor);
+            return new[] { SyntaxFactory.Interpolation(expression) };
         }
 
         /// <summary>

Tests/CSharp/ExpressionTests/XmlExpressionTests.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Threading.Tasks;
+using ICSharpCode.CodeConverter.Tests.TestRunners;
+using Xunit;
+
+namespace ICSharpCode.CodeConverter.Tests.CSharp.ExpressionTests
+{
+    /// <summary>
+    /// See https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/language-features/xml/how-to-transform-xml-by-using-linq
+    /// </summary>
+    public class XmlExpressionTests : ConverterTestBase
+    {
+        [Fact]
+        public async Task NestedXmlEchoSimpleAsync()
+        {
+            await TestConversionVisualBasicToCSharpAsync(@"Class TestClass
+    Private Sub TestMethod()
+        Dim hello = ""Hello""
+        dim x = <h1><%= hello %></h1>
+    End Sub
+End Class", @"using System.Xml.Linq;
+
+internal partial class TestClass
+{
+    private void TestMethod()
+    {
+        string hello = ""Hello"";
+        XElement x = XElement.Parse($""<h1>{hello}</h1>"");
+    }
+}");
+        }
+        [Fact]
+        public async Task TwoLayerNestedXmlWithExpressionsAsync()
+        {
+            await TestConversionVisualBasicToCSharpAsync(@"Class TestClass
+    Private Sub TestMethod()
+        Dim var1 = 1
+        Dim var2 = 2
+        dim x = <h1><%= var1 %><%= var2 %><span><%= var2 %><%= var1 %></span></h1>
+    End Sub
+End Class", @"using System.Xml.Linq;
+
+internal partial class TestClass
+{
+    private void TestMethod()
+    {
+        int var1 = 1;
+        int var2 = 2;
+        XElement x = XElement.Parse($""<h1>{var1}{var2}<span>{var2}{var1}</span> </h1>"");
+    }
+}");
+        }
+    }
+}