set the file extension form CodeDomProvider;

make the temp file readonly

src/Main/Base/Project/Src/Editor/Commands/GoToDefinition.cs

@@ -56,6 +56,10 @@ namespace ICSharpCode.SharpDevelop.Editor.Commands
 				
 				// jump to definition
 				var info = ParserService.ParseFile(filePath);
+				
+				if (info == null)
+					return;
+				
 				int line = 0, col = 0;
 				foreach(var c in info.CompilationUnit.Classes) {
 					if (s.ResolvedMember.EntityType == EntityType.Event) {

src/Main/Base/Project/Src/Services/DecompilerService/DecompilerService.cs

@@ -311,15 +311,8 @@ namespace ICSharpCode.SharpDevelop
 		{
 			// temp file
 			string tempFolder = Path.GetTempPath();
-			string file = fileName + ".temp";
-			if (ProjectService.CurrentProject != null) {
-				string language = ProjectService.CurrentProject.Language.ToLower();
-				if (language == "c#" || language == "csharp")
-					file += ".cs";
-				else
-					if (language == "vb" || language == "vbnet")
-						file += ".vb";
-			}
+			string file = fileName + ".temp." + 
+				ProjectService.CurrentProject.LanguageProperties.CodeDomProvider.FileExtension;
 						
 			string filePath = Path.Combine(tempFolder, file);
 
@@ -337,6 +330,8 @@ namespace ICSharpCode.SharpDevelop
 						sw,
 						new CodeGeneratorOptions());
 			}
+			
+			File.SetAttributes(filePath, FileAttributes.ReadOnly);			
 			return filePath;
 		}
 	}