How to write a loop, or lambda expression, in the immediate window, part 2

$dte is the key.

That whole nuget package manager console window, that is a powershell window, that gives you easy access to the visual studio automation model, is neat, very powerful, and, as I have discovered, a treasure trove of Visual Studio arcana.

EnvDTE.DTE is easy to get at when you are in the context of an add-in that you have written yourself. Exposing it in ready made powershell window, is a complex and involved trick. Writing that whole powershell console as an add-in inside of Visual Studio, after reading the source code at nuget.codeplex.com, appears to be an elegant work of coding art.

But.. back to $dte, my favorite powershell-nuget-visualstudio variable. Here is the code that worked the magic and populated the variable inside of powershell:

http://nuget.codeplex.com/SourceControl/latest#src/VsConsole/PowerShellHost/RunspaceManager.cs

 

        [System.Diagnostics.CodeAnalysis.SuppressMessage(
            "Microsoft.Reliability",
            "CA2000:Dispose objects before losing scope",
            Justification = "We can't dispose it if we want to return it.")]
        private static Tuple CreateRunspace(IConsole console, string hostName)
        {
            DTE dte = ServiceLocator.GetInstance();

InitialSessionState initialSessionState = InitialSessionState.CreateDefault();
            initialSessionState.Variables.Add(
                new SessionStateVariableEntry(
                    "DTE",
                    (DTE2)dte,
                    "Visual Studio DTE automation object",
                    ScopedItemOptions.AllScope | ScopedItemOptions.Constant)
            );

// this is used by the functional tests
            var packageManagerFactory = ServiceLocator.GetInstance();
            var pmfTuple = Tuple.Create<string, object>("packageManagerFactory", packageManagerFactory);

Tuple<string, object>[] privateData = new Tuple<string, object>[] { pmfTuple };

var host = new NuGetPSHost(hostName, privateData)
            {
                ActiveConsole = console
            };

var runspace = RunspaceFactory.CreateRunspace(host, initialSessionState);
            runspace.ThreadOptions = PSThreadOptions.Default;
            runspace.Open();

//
            // Set this runspace as DefaultRunspace so I can script DTE events.
            //
            // WARNING: MSDN says this is unsafe. The runspace must not be shared across
            // threads. I need this to be able to use ScriptBlock for DTE events. The
            // ScriptBlock event handlers execute on DefaultRunspace.
            //
            Runspace.DefaultRunspace = runspace;

return Tuple.Create(new RunspaceDispatcher(runspace), host);
        }

 

Pasted from <http://nuget.codeplex.com/SourceControl/latest>

 

 

So here is what I learned from strolling down this rabbit hole.

1. They brute forced the whole console window. They didn't recycle any sort of existing powershell or command window. They wrote a new one and dealt with all the keypress by keypress nastiness that is involved therein.
2. $dte is actually spelled $DTE, and just a variable passed into a Runspace through its InitialSessionState.
3. OpenSource code is fun.

Also, and unrelated to codeplex and nuget, if you want to create a headless $dte object, or rather one connected to a new instance of visual studio 2012, that is simply:

$dte = New-Object -comobject VisualStudio.DTE.11.0

Getting the running obect is done like this:

$dte = [System.Runtime.InteropSrevices.Marshal]::GetActiveObject("VisualStudio.DTE.11.0")

How to write a loop, or lambda expression, in the immediate window

First, you can't write lambda expressions in the immediate window. There are some very good, boring reasons why this is the case. Jared Par explains here...

However, what you really wanted to do is write a loop inside the immediate window because there is some particular debugging goal that you are trying to achieve. This post is about how you can do that.

For example, let's say we have an array of a large number of elements, 1000 or so should do. Let's also say that there is one piece of data in that array that is relevant. We wish to inspect each element individually and test the validity of each item. The following code snipped creates this situation.

static void Main(string[] args)
{ 
  List<int> ints = new List<int>();
  for (int i = 0; i < 1000; i++)
  {
    ints.Add(i);
  }  
  Random random = new Random();
  ints[random.Next(1000)] = -12;
  Console.ReadLine();
}

In this artificial case we're looking for the index of the element in the array that is equal to -12.

The immediate window forces us to do this one item in the array at a time. Potentially taking 1000 user-interactive steps.

Since that method sucks, here's an alternative:

1. Run the program in the debugger and set a breakpoint on the ReadLine() statement.
2. Open up the nuget package manager console.
3. Write some clever powershell that does the evaluation and looping for us.

The clever bit of powershell code that is necessary starts with something like this:

$dte.Debugger.GetExpression("expression", 1, $true)

$dte is the variable that contains the Visual Studio automation model.
Documentation about $dte is here.

In our case, the completed powershell expression looks like this:

for($i = 0; $i -lt 1000; $i++) { $a = $dte.Debugger.GetExpression("ints[$i]"); if ($a.Value -ne $i) { Write-Host $a.Value $i } }

Or, broken into multiple, more readable lines:

for($i = 0; $i -lt 1000; $i++) {
  $a = $dte.Debugger.GetExpression("ints[$i]");
  if ($a.Value -ne $i) {
    Write-Host $a.Value $i
  }
}

This rather neatly writes out the index we're looking for and the value found there. 

The anomalous value (-12) wound up in the 604th element of the array. Groovy.

Most programmers aren't going to do this. It requires good knowledge of powershell, some knowledge of the Visual Studio automation model, and an interesting and difficult debugging problem before it is useful.

But it is fun.

Edit.FormatDocument

Also goes by Cntrl-E + D.

I had a document with all the formatting messed up. Tabs were spaces, and they were 4 instead of 2 which is the standard here. I typed these 3 keys, and everything was magically fixed. Groovy.

The stack overflow answer that got me here.

This is just another time saving shortcut that I'm trying to remember.

Is it leaking?

I wondered if my program was leaking. Here's how I found out:
Using Visual Studio 2012, into the immediate window, I typed:

.load SOS

Then, I investigated my class with this command (still in the immediate window).

!DumpHeap -type

I could see how many objects there were of this type in the heap. I could see their addresses in memory.

!gcroot

This command showed me where they came from and what other objects had references to them.

Finally:

!finalizequeue -allready

This allowed me to verify that although the object wasn't finalized yet, it was due to be whenever the Garbage Collector got around to it and therefore, my program wasn't leaking.