Guard against null root - fixes #457 (followup)

Author: GrahamTheCoder

CHANGELOG.md

@@ -8,6 +8,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### Vsix
 
+* Fixed error caused when converting with "Copy to clipboard" option enabled
+
 ### VB -> C#
 * Add modifier for nested types
 * Remove body for converted extern methods

ICSharpCode.CodeConverter/CSharp/VisualBasicConverter.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Editing;
@@ -15,11 +16,21 @@ public static async Task<SyntaxNode> ConvertCompilationTree(Document document,
             var compilation = await document.Project.GetCompilationAsync();
             var tree = await document.GetSyntaxTreeAsync();
             var semanticModel = compilation.GetSemanticModel(tree, true);
-            var root = (VBasic.VisualBasicSyntaxNode)await document.GetSyntaxRootAsync();
+            var root = await document.GetSyntaxRootAsync() as VBasic.VisualBasicSyntaxNode ??
+                       throw new InvalidOperationException(NullRootError(document));
+
             var csSyntaxGenerator = SyntaxGenerator.GetGenerator(csharpReferenceProject);
             var visualBasicSyntaxVisitor = new
                 DeclarationNodeVisitor(document, compilation, semanticModel, csharpViewOfVbSymbols, csSyntaxGenerator);
             return await root.Accept(visualBasicSyntaxVisitor.TriviaConvertingVisitor);
         }
+
+        private static string NullRootError(Document document)
+        {
+            string initial = document.Project.Language != LanguageNames.VisualBasic
+                ? "Document cannot be converted because it's not within a VB project."
+                : "Could not find valid VB within document.";
+            return initial + " For best results, convert a VB document from within a VB project which compiles successfully.";
+        }
     }
 }

ICSharpCode.CodeConverter/VB/CSharpConverter.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Editing;
 using Microsoft.CodeAnalysis.VisualBasic;
@@ -15,11 +16,20 @@ public static async Task<SyntaxNode> ConvertCompilationTree(Document document,
             var compilation = await document.Project.GetCompilationAsync();
             var tree = await document.GetSyntaxTreeAsync();
             var semanticModel = compilation.GetSemanticModel(tree, true);
-            var root = (CS.CSharpSyntaxNode) await document.GetSyntaxRootAsync();
+            var root = await document.GetSyntaxRootAsync() as CS.CSharpSyntaxNode ??
+                       throw new InvalidOperationException(NullRootError(document));
 
             var vbSyntaxGenerator = SyntaxGenerator.GetGenerator(vbReferenceProject);
             var visualBasicSyntaxVisitor = new NodesVisitor(document, (CS.CSharpCompilation) compilation, semanticModel, vbViewOfCsSymbols, vbSyntaxGenerator);
             return root.Accept(visualBasicSyntaxVisitor.TriviaConvertingVisitor);
         }
+
+        private static string NullRootError(Document document)
+        {
+            var initial = document.Project.Language != LanguageNames.CSharp
+                ? "Document cannot be converted because it's not within a C# project."
+                : "Could not find valid C# within document.";
+            return initial + " For best results, convert a c# document from within a C# project which compiles successfully.";
+        }
     }
 }