Don't lose OutputWindow contents after reload

After project/solution conversion a reload will be needed, so it's kind of annoying to destroy the log
Could refine this more to only restore the log in that particular circumstance, but there seems little to lose doing it all the time.

Author: GrahamTheCoder

Vsix/CodeConversion.cs

@@ -24,6 +24,7 @@ class CodeConversion
         private readonly VisualStudioWorkspace _visualStudioWorkspace;
         public static readonly string ConverterTitle = "Code converter";
         private static readonly string Intro = Environment.NewLine + Environment.NewLine + new string(Enumerable.Repeat('-', 80).ToArray()) + Environment.NewLine + "Writing converted files to disk:";
+        private VisualStudioInteraction.OutputWindow _outputWindow;
         private string SolutionDir => Path.GetDirectoryName(_visualStudioWorkspace.CurrentSolution.FilePath);
 
         public CodeConversion(IServiceProvider serviceProvider, VisualStudioWorkspace visualStudioWorkspace,
@@ -32,6 +33,7 @@ public CodeConversion(IServiceProvider serviceProvider, VisualStudioWorkspace vi
             GetOptions = getOptions;
             _serviceProvider = serviceProvider;
             _visualStudioWorkspace = visualStudioWorkspace;
+            _outputWindow = new VisualStudioInteraction.OutputWindow();
         }
 
         public async Task PerformProjectConversion<TLanguageConversion>(IReadOnlyCollection<Project> selectedProjects) where TLanguageConversion : ILanguageConversion, new()
@@ -52,7 +54,7 @@ await Task.Run(() => {
 
             if (GetOptions().CopyResultToClipboardForSingleDocument) {
                 Clipboard.SetText(conversionResult.ConvertedCode ?? conversionResult.GetExceptionsAsString());
-                VisualStudioInteraction.OutputWindow.WriteToOutputWindow("Conversion result copied to clipboard.");
+                _outputWindow.WriteToOutputWindow("Conversion result copied to clipboard.");
                 VisualStudioInteraction.ShowMessageBox(_serviceProvider, "Conversion result copied to clipboard.", conversionResult.GetExceptionsAsString(), false);
             }
 
@@ -66,8 +68,9 @@ private void WriteConvertedFilesAndShowSummary(IEnumerable<ConversionResult> con
             string longestFilePath = null;
             var longestFileLength = -1;
 
-            VisualStudioInteraction.OutputWindow.WriteToOutputWindow(Intro);
-            VisualStudioInteraction.OutputWindow.ForceShowOutputPane();
+            _outputWindow.Clear();
+            _outputWindow.WriteToOutputWindow(Intro);
+            _outputWindow.ForceShowOutputPane();
 
             foreach (var convertedFile in convertedFiles) {
                 if (convertedFile.SourcePathOrNull == null) continue;
@@ -96,8 +99,8 @@ private void FinalizeConversion(List<string> files, List<string> errors, string
         {
             var options = GetOptions();
             var conversionSummary = GetConversionSummary(files, errors);
-            VisualStudioInteraction.OutputWindow.WriteToOutputWindow(conversionSummary);
-            VisualStudioInteraction.OutputWindow.ForceShowOutputPane();
+            _outputWindow.WriteToOutputWindow(conversionSummary);
+            _outputWindow .ForceShowOutputPane();
 
             if (longestFilePath != null)
             {
@@ -113,14 +116,14 @@ private void FinalizeConversion(List<string> files, List<string> errors, string
             if (shouldOverwriteSolutionAndProjectFiles)
             {
                 var titleMessage = options.CreateBackups ? "Creating backups and overwriting files:" : "Overwriting files:" + "";
-                VisualStudioInteraction.OutputWindow.WriteToOutputWindow(titleMessage);
+                _outputWindow.WriteToOutputWindow(titleMessage);
                 foreach (var fileToOverwrite in filesToOverwrite)
                 {
                     if (options.CreateBackups) File.Copy(fileToOverwrite.SourcePathOrNull, fileToOverwrite.SourcePathOrNull + ".bak", true);
                     File.WriteAllText(fileToOverwrite.TargetPathOrNull, fileToOverwrite.ConvertedCode);
 
                     var targetPathRelativeToSolutionDir = PathRelativeToSolutionDir(fileToOverwrite.TargetPathOrNull);
-                    VisualStudioInteraction.OutputWindow.WriteToOutputWindow(Environment.NewLine + $"* {targetPathRelativeToSolutionDir}");
+                    _outputWindow.WriteToOutputWindow(Environment.NewLine + $"* {targetPathRelativeToSolutionDir}");
                 }
             }
         }
@@ -163,7 +166,7 @@ private void LogProgress(ConversionResult convertedFile, List<string> errors)
                 output += $" contains errors{Environment.NewLine}    {indentedException}";
             }
 
-            VisualStudioInteraction.OutputWindow.WriteToOutputWindow(output);
+            _outputWindow.WriteToOutputWindow(output);
         }
 
         private string PathRelativeToSolutionDir(string path)

Vsix/VisualStudioInteraction.cs

@@ -5,6 +5,7 @@
 using System.Linq;
 using System.Reflection;
 using System.Runtime.InteropServices;
+using System.Text;
 using EnvDTE;
 using EnvDTE80;
 using Microsoft.VisualStudio;
@@ -147,12 +148,25 @@ public static bool ShowMessageBox(IServiceProvider serviceProvider, string title
                 defaultOk || !showCancelButton ? OLEMSGDEFBUTTON.OLEMSGDEFBUTTON_FIRST : OLEMSGDEFBUTTON.OLEMSGDEFBUTTON_SECOND) == answeredOk;
         }
 
-        public static class OutputWindow
+        public class OutputWindow
         {
             private const string PaneName = "Code Converter";
             private static readonly Guid PaneGuid = new Guid("44F575C6-36B5-4CDB-AAAE-E096E6A446BF");
-            private static readonly Lazy<IVsOutputWindowPane> OutputPane = new Lazy<IVsOutputWindowPane>(CreateOutputPane);
-            
+            private readonly IVsOutputWindowPane _outputPane;
+            private readonly StringBuilder _cachedOutput = new StringBuilder();
+
+            // Reference to avoid GC https://docs.microsoft.com/en-us/dotnet/api/envdte.solutionevents?view=visualstudiosdk-2017#remarks
+            // ReSharper disable once PrivateFieldCanBeConvertedToLocalVariable
+            private readonly SolutionEvents _solutionEvents;
+
+            public OutputWindow()
+            {
+                _outputPane = CreateOutputPane();
+
+                _solutionEvents = Dte.Events.SolutionEvents;
+                _solutionEvents.Opened += () => { WriteToOutputWindow(_cachedOutput.ToString()); };
+            }
+
             private static IVsOutputWindow GetOutputWindow()
             {
                 IServiceProvider serviceProvider = new ServiceProvider(Dte as Microsoft.VisualStudio.OLE.Interop.IServiceProvider);
@@ -161,9 +175,8 @@ private static IVsOutputWindow GetOutputWindow()
             private static IVsOutputWindowPane CreateOutputPane()
             {
                 Guid generalPaneGuid = PaneGuid;
-                IVsOutputWindowPane pane;
                 var outputWindow = GetOutputWindow();
-                outputWindow.GetPane(ref generalPaneGuid, out pane);
+                outputWindow.GetPane(ref generalPaneGuid, out var pane);
 
                 if (pane == null) {
                     outputWindow.CreatePane(ref generalPaneGuid, PaneName, 1, 1);
@@ -173,15 +186,22 @@ private static IVsOutputWindowPane CreateOutputPane()
                 return pane;
             }
 
-            public static void ForceShowOutputPane()
+            public void Clear()
+            {
+                _cachedOutput.Clear();
+                _outputPane.Clear();
+            }
+
+            public void ForceShowOutputPane()
             {
                 Dte.Windows.Item(EnvDTE.Constants.vsWindowKindOutput).Visible = true;
-                OutputPane.Value.Activate();
+                _outputPane.Activate();
             }
 
-            public static void WriteToOutputWindow(string message)
+            public void WriteToOutputWindow(string message)
             {
-                OutputPane.Value.OutputString(message);
+                _cachedOutput.AppendLine(message);
+                _outputPane.OutputString(message);
             }
         }
     }