Code action requests from other extensions crash the language server

This change fixes PowerShell/vscode-powershell#408 which states that code
action requests sent for diagnostic markers created by other extensions
cause our language server to crash.  This was due to us not handling the
case where irrelevant diagnostics might (mistakenly?) get sent to us to
resolve their code actions.

Author: daviwil

src/PowerShellEditorServices.Protocol/LanguageServer/Diagnostics.cs

@@ -71,6 +71,11 @@ public class Diagnostic
         /// Gets or sets the diagnostic message.
         /// </summary>
         public string Message { get; set; }
+
+        /// <summary>
+        /// Gets or sets the source of the diagnostic message.
+        /// </summary>
+        public string Source { get; set; }
     }
 }
 

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -27,6 +27,7 @@ namespace Microsoft.PowerShell.EditorServices.Protocol.Server
     public class LanguageServer : LanguageServerBase
     {
         private static CancellationTokenSource existingRequestCancellation;
+        private readonly static string DiagnosticSourceName = "PowerShellEditorServices";
 
         private bool profilesLoaded;
         private EditorSession editorSession;
@@ -994,7 +995,9 @@ protected async Task HandleCodeActionRequest(
             {
                 foreach (var diagnostic in codeActionParams.Context.Diagnostics)
                 {
-                    if (markerIndex.TryGetValue(diagnostic.Code, out correction))
+                    if (string.Equals(diagnostic.Source, DiagnosticSourceName, StringComparison.CurrentCultureIgnoreCase) &&
+                        !string.IsNullOrEmpty(diagnostic.Code) &&
+                        markerIndex.TryGetValue(diagnostic.Code, out correction))
                     {
                         codeActionCommands.Add(
                             new CodeActionCommand
@@ -1335,9 +1338,9 @@ private static Diagnostic GetDiagnosticFromMarker(ScriptFileMarker scriptFileMar
                 Severity = MapDiagnosticSeverity(scriptFileMarker.Level),
                 Message = scriptFileMarker.Message,
                 Code = Guid.NewGuid().ToString(),
+                Source = DiagnosticSourceName,
                 Range = new Range
                 {
-                    // TODO: What offsets should I use?
                     Start = new Position
                     {
                         Line = scriptFileMarker.ScriptRegion.StartLineNumber - 1,