Extensions.DotNet.Interactive - Add ENV to control disposal of tmp dir (#952)

Author: suhsteve

src/csharp/Extensions/Microsoft.Spark.Extensions.DotNet.Interactive/AssemblyKernelExtension.cs

@@ -25,6 +25,7 @@ namespace Microsoft.Spark.Extensions.DotNet.Interactive
     public class AssemblyKernelExtension : IKernelExtension
     {
         private const string TempDirEnvVar = "DOTNET_SPARK_EXTENSION_INTERACTIVE_TMPDIR";
+        private const string PreserveTempDirEnvVar = "DOTNET_SPARK_EXTENSION_INTERACTIVE_PRESERVE_TMPDIR";
 
         private readonly PackageResolver _packageResolver =
             new PackageResolver(new SupportNugetWrapper());
@@ -41,7 +42,11 @@ public Task OnLoadAsync(Kernel kernel)
                 Environment.SetEnvironmentVariable(Constants.RunningREPLEnvVar, "true");
 
                 DirectoryInfo tempDir = CreateTempDirectory();
-                compositeKernel.RegisterForDisposal(new DisposableDirectory(tempDir));
+
+                if (!EnvironmentUtils.GetEnvironmentVariableAsBool(PreserveTempDirEnvVar))
+                {
+                    compositeKernel.RegisterForDisposal(new DisposableDirectory(tempDir));
+                }
 
                 compositeKernel.AddMiddleware(async (command, context, next) =>
                 {