Debugging Extensions

Debugging Visual Studio extensions requires running a second instance of VS - the Experimental Instance. This keeps your main VS installation clean while testing.

The Experimental Instance

When you press F5 to debug your extension, Visual Studio launches a separate instance with its own:

• Settings and configurations
• Installed extensions
• Window layouts
• Recent projects

This isolation means:

• Your extension won’t crash your main VS
• You can test different configurations
• You can easily reset to a clean state

Starting a Debug Session

1. Set your VSIX project as the startup project
2. Press F5 or go to Debug > Start Debugging
3. A new VS instance opens with “(Experimental Instance)” in the title bar
4. Your extension is automatically installed and loaded

Setting Breakpoints

Set breakpoints in your extension code just like any other project:

protected override async Task ExecuteAsync(OleMenuCmdEventArgs e)
{
    // Set a breakpoint on the next line
    var docView = await VS.Documents.GetActiveDocumentViewAsync();

    if (docView?.TextView != null)
    {
        // Your code here
    }
}

When you trigger your command in the Experimental Instance, the debugger breaks at your breakpoint.

Debug Output

Use the Output window to see diagnostic information:

protected override async Task ExecuteAsync(OleMenuCmdEventArgs e)
{
    await VS.StatusBar.ShowMessageAsync("Command started...");

    try
    {
        // Your code here
        System.Diagnostics.Debug.WriteLine("Command executed successfully");
    }
    catch (Exception ex)
    {
        System.Diagnostics.Debug.WriteLine($"Error: {ex.Message}");
    }
}

View output in View > Output and select “Debug” from the dropdown.

ActivityLog.xml

Visual Studio logs detailed information to ActivityLog.xml:

Location:

%APPDATA%\Microsoft\VisualStudio\17.0_<hash>Exp\ActivityLog.xml

To enable verbose logging:

1. Start VS with /Log command line argument
2. Or set VSLOGENABLED=1 environment variable

Resetting the Experimental Instance

If the Experimental Instance gets corrupted or you want a fresh start:

Method 1: Visual Studio

1. Close all VS instances
2. Open Developer Command Prompt for VS 2022
3. Run: devenv /ResetSettings Exp

Method 2: Delete User Data

1. Close all VS instances
2. Delete the folder: %LOCALAPPDATA%\Microsoft\VisualStudio\17.0_<hash>Exp

Method 3: Reset All

# From Developer Command Prompt
devenv /ResetSettings Exp
devenv /ClearCache Exp

Common Debugging Issues

Extension Not Loading

Check these common issues:

1. Missing attributes - Ensure your package has [PackageRegistration]
2. Async loading - Use AllowsBackgroundLoading = true
3. Missing dependencies - Check your NuGet references
4. MEF errors - Look in ActivityLog.xml for composition errors

Breakpoints Not Hit

1. Symbols not loaded - Ensure PDB files are included
2. Wrong instance - Make sure you’re debugging the right VS
3. Background thread - Use JoinableTaskFactory.SwitchToMainThreadAsync()

Package Load Failure

Check the error message in VS and ActivityLog.xml:

SetSite failed for package [YourPackageGuid]

Common causes:

• Exception in InitializeAsync
• Missing service dependency
• COM registration issue

Debug Configuration

Your .csproj should include debug settings:

<PropertyGroup Condition="'$(Configuration)' == 'Debug'">
  <StartAction>Program</StartAction>
  <StartProgram>$(DevEnvDir)devenv.exe</StartProgram>
  <StartArguments>/rootsuffix Exp</StartArguments>
</PropertyGroup>

The /rootsuffix Exp argument launches the Experimental Instance.

Next Steps

Once your extension is working, learn about Packaging and Publishing to share it with others.