extending-open-folder

Open Folder Extensibility in Visual Studio

Open Folder lets users open any codebase in Visual Studio without a project or solution file. Extensions can enhance this experience by providing:

• File context providers — supply build, debug, or language contexts for files
• File context actions — attach right-click actions to custom file types
• File scanners — scan files for symbols that appear in Go To (Ctrl+,)
• Workspace settings — read and write per-folder settings stored in .vs/VSWorkspaceSettings.json

All Open Folder APIs are in the Microsoft.VisualStudio.Workspace.* namespaces and are MEF-based.

Open Folder extensibility matters when your extension needs to work outside the traditional project/solution model — for example, supporting lightweight editing of Python, Rust, Go, or JavaScript projects that don't use MSBuild. Without Open Folder providers, VS treats these folders as inert file trees with no build, navigation, or debug support.

When to use Open Folder vs. alternatives:

• Custom build/debug contexts for non-MSBuild file types → Open Folder file context providers (this skill)
• Symbol scanning for Go To in non-project files → Open Folder file scanners (this skill)
• Full language support (completion, diagnostics, navigation) → vs-language-server (works alongside Open Folder)
• Adding context menu actions in Solution Explorer for project files → vs-context-menu
• Reacting to solution/project open/close events → vs-solution-events

VisualStudio.Extensibility (out-of-process)

Not supported. The new extensibility model does not have Open Folder workspace APIs. The Microsoft.VisualStudio.Workspace.* APIs require in-process MEF composition. If your VisualStudio.Extensibility extension needs Open Folder support, use an in-process hybrid component.

---

VSSDK / VSIX Community Toolkit (in-process)

The Toolkit and VSSDK approaches are identical for Open Folder — all workspace extensibility uses the same MEF-based Microsoft.VisualStudio.Workspace.* APIs.

NuGet packages:

• Microsoft.VisualStudio.SDK (≥ 17.0)
• Microsoft.VisualStudio.Workspace.Extensions (contains the workspace API types)

Key namespaces:

• Microsoft.VisualStudio.Workspace
• Microsoft.VisualStudio.Workspace.Build
• Microsoft.VisualStudio.Workspace.Extensions.VS
• Microsoft.VisualStudio.Workspace.Indexing
• Microsoft.VisualStudio.Workspace.Settings

File organization

MyExtension/
├── OpenFolder/
│   ├── MyFileContextProvider.cs
│   ├── MyFileActionProvider.cs
│   ├── MyFileScanner.cs
│   └── MySettingsProvider.cs
├── MyExtensionPackage.cs
├── source.extension.vsixmanifest
└── MyExtension.csproj

VSIX manifest — MEF asset

Open Folder providers are discovered through MEF. Add the MefComponent asset to your source.extension.vsixmanifest:

<Assets>
  <Asset Type="Microsoft.VisualStudio.MefComponent" d:Source="Project" d:ProjectName="%CurrentProject%" Path="|%CurrentProject%|" />
</Assets>

---

1. File Context Providers

File context providers supply metadata about files — build contexts, debug contexts, or custom data. The workspace matches consumer requests to providers based on the context type GUID.

OpenFolder/MyFileContextProvider.cs:

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.VisualStudio.Workspace;

namespace MyExtension.OpenFolder;

// The factory creates a provider instance per workspace
[ExportFileContextProvider(
    ProviderType,
    PackageIds.BuildContextTypeGuid)]  // The context type GUID this provider produces
internal class MyBuildContextProviderFactory : IWorkspaceProviderFactory<IFileContextProvider>
{
    private const string ProviderType = "9A31D832-5AB2-4E1A-A446-5B4E5AC58A3A";

    public IFileContextProvider CreateProvider(IWorkspace workspace)
    {
        return new MyBuildContextProvider(workspace);
    }
}

internal class MyBuildContextProvider : IFileContextProvider
{
    private readonly IWorkspace workspace;

    public MyBuildContextProvider(IWorkspace workspace)
    {
        this.workspace = workspace;
    }

    public async Task<IReadOnlyCollection<FileContext>> GetContextsForFileAsync(
        string filePath,
        CancellationToken cancellationToken)
    {
        // Only provide context for .mylang files
        if (!filePath.EndsWith(".mylang", StringComparison.OrdinalIgnoreCase))
        {
            return Array.Empty<FileContext>();
        }

        var context = new FileContext(
            new Guid("9A31D832-5AB2-4E1A-A446-5B4E5AC58A3A"),  // Provider GUID
            BuildContextTypes.BuildContextType,                   // Context type
            filePath,
            new[] { filePath });

        return new[] { context };
    }
}

Built-in context type GUIDs

Constant	Purpose
BuildContextTypes.BuildContextType	Build contexts for the Build menu
BuildContextTypes.RebuildContextType	Rebuild contexts
BuildContextTypes.CleanContextType	Clean contexts

---

2. File Context Actions

File context actions add entries to the right-click context menu for files in Solution Explorer (Open Folder mode).

OpenFolder/MyFileActionProvider.cs:

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.VisualStudio.Workspace;
using Microsoft.VisualStudio.Workspace.Extensions.VS;

namespace MyExtension.OpenFolder;

[ExportFileContextActionProvider(
    (FileContextActionProviderOptions)0,   // No special options
    ProviderType,
    PackageIds.BuildContextTypeGuid)]       // Apply to build contexts
internal class MyFileActionProviderFactory : IWorkspaceProviderFactory<IFileContextActionProvider>
{
    private const string ProviderType = "B1C3F8A5-2D4E-4F6A-8B9C-1E2D3F4A5B6C";

    public IFileContextActionProvider CreateProvider(IWorkspace workspace)
    {
        return new MyFileActionProvider();
    }
}

internal class MyFileActionProvider : IFileContextActionProvider
{
    public Task<IReadOnlyList<IFileContextAction>> GetActionsAsync(
        string filePath,
        FileContext fileContext,
        CancellationToken cancellationToken)
    {
        var actions = new List<IFileContextAction>
        {
            new WordCountAction(filePath)
        };

        return Task.FromResult<IReadOnlyList<IFileContextAction>>(actions);
    }
}

internal class WordCountAction : IFileContextAction
{
    private readonly string filePath;

    public WordCountAction(string filePath)
    {
        this.filePath = filePath;
    }

    public string DisplayName => "Count Words";

    public async Task<IFileContextActionResult> ExecuteAsync(
        IProgress<IFileContextActionProgressUpdate> progress,
        CancellationToken cancellationToken)
    {
        string text = File.ReadAllText(filePath);
        int wordCount = text.Split(
            new[] { ' ', '\t', '\r', '\n' },
            StringSplitOptions.RemoveEmptyEntries).Length;

        // Show result — use VS.MessageBox if using Toolkit, or
        // IVsUIShell message box for pure VSSDK
        System.Windows.Forms.MessageBox.Show(
            $"Word count: {wordCount}",
            "Word Count",
            System.Windows.Forms.MessageBoxButtons.OK,
            System.Windows.Forms.MessageBoxIcon.Information);

        return new FileContextActionResult(true);
    }
}

---

3. File Scanners (Symbol Providers)

File scanners extract symbol information from custom file types so they appear in Go To (Ctrl+,) and Navigate To.

OpenFolder/MyFileScanner.cs:

using System;
using System.Collections.Generic;
using System.IO;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.VisualStudio.Workspace;
using Microsoft.VisualStudio.Workspace.Indexing;

namespace MyExtension.OpenFolder;

[ExportFileScannerProvider(
    ProviderType,
    "File")]                    // Scanner attribute type
internal class MyFileScannerProviderFactory : IWorkspaceProviderFactory<IFileScanner>
{
    private const string ProviderType = "D4E5F6A7-8B9C-1D2E-3F4A-5B6C7D8E9F10";

    public IFileScanner CreateProvider(IWorkspace workspace)
    {
        return new MyFileScanner();
    }
}

internal class MyFileScanner : IFileScanner
{
    // Declare which kinds of data this scanner produces
    public IReadOnlyCollection<FileDataValue> ReadableFileDataTypes { get; } = new[]
    {
        FileDataValue.FileSymbolType
    };

    public async Task<T[]> ReadFileAsync<T>(string filePath, CancellationToken cancellationToken)
        where T : class
    {
        // Only scan .mylang files
        if (!filePath.EndsWith(".mylang", StringComparison.OrdinalIgnoreCase))
        {
            return Array.Empty<T>();
        }

        if (typeof(T) != typeof(FileSymbol))
        {
            return Array.Empty<T>();
        }

        var symbols = new List<FileSymbol>();
        string[] lines = await Task.Run(() => File.ReadAllLines(filePath), cancellationToken);

        // Simple pattern: lines starting with "func " define a function symbol
        var funcPattern = new Regex(@"^func\s+(\w+)", RegexOptions.Compiled);

        for (int i = 0; i < lines.Length; i++)
        {
            var match = funcPattern.Match(lines[i]);
            if (match.Success)
            {
                symbols.Add(new FileSymbol(
                    match.Groups[1].Value,          // Symbol name
                    SymbolKind.Function,
                    new TextSpan(i, 0, i, lines[i].Length),
                    filePath));
            }
        }

        return symbols.Cast<T>().ToArray();
    }
}

---

4. Workspace Settings

Open Folder stores per-folder settings in .vs/VSWorkspaceSettings.json. Extensions can read and write these settings.

Reading settings

using Microsoft.VisualStudio.Workspace;
using Microsoft.VisualStudio.Workspace.Settings;

private void ReadSettings(IWorkspace workspace)
{
    IWorkspaceSettingsManager settingsManager = workspace.GetSettingsManager();
    IWorkspaceSettings settings = settingsManager.GetAggregatedSettings(SettingsTypes.Generic);

    // Read typed values
    WorkspaceSettingsResult result = settings.GetProperty("myext.maxItems", out int maxItems);
    if (result == WorkspaceSettingsResult.Success)
    {
        // Use maxItems
    }

    // Extension method with default
    string outputDir = settings.Property("myext.outputDir", /* default */ "bin");
}

Providing dynamic settings

Implement IWorkspaceSettingsProviderFactory to provide settings programmatically:

using System.ComponentModel.Composition;
using Microsoft.VisualStudio.Workspace;
using Microsoft.VisualStudio.Workspace.Settings;

[Export(typeof(IWorkspaceSettingsProviderFactory))]
internal class MySettingsProviderFactory : IWorkspaceSettingsProviderFactory
{
    public int Priority => 200;  // Lower = higher priority; built-in is ~100

    public IWorkspaceSettingsProvider CreateSettingsProvider(IWorkspace workspace)
    {
        return new MySettingsProvider(workspace);
    }
}

Settings scope hierarchy

Settings are aggregated across scopes (highest to lowest priority):

1. .vs/ folder ("local settings") at workspace root
2. The requested file's directory
3. Parent directories up to workspace root
4. User-global settings directory

---

Auto-loading packages in Open Folder mode

To auto-load your package when a folder is opened (instead of a solution), use the Open Folder UI context:

[ProvideAutoLoad(
    "4646B819-1AE0-4E79-97F4-8A8176FDD664",  // Open Folder UI context GUID
    PackageAutoLoadFlags.BackgroundLoad)]
public sealed class MyExtensionPackage : ToolkitPackage
{
    // ...
}

You can also implement IVsSolutionEvents7 for folder open/close events:

public void OnAfterOpenFolder(string folderPath)
{
    // Folder was opened — initialize workspace-related features
}

public void OnAfterCloseFolder(string folderPath)
{
    // Folder was closed — clean up
}

---

Troubleshooting

"The SourceExplorerPackage package did not load correctly"

This usually means a MEF composition error. Check the error log at:

%LOCALAPPDATA%\Microsoft\VisualStudio\17.0_<id>\ComponentModelCache\Microsoft.VisualStudio.Default.err

Common causes:

• Export attribute type doesn't match the implemented interface (e.g. exporting IFileContextProvider but implementing IFileContextActionProvider)
• Missing MEF asset in source.extension.vsixmanifest

Grammar/colorization not working in Open Folder

TextMate grammars work in Open Folder out of the box. If colorization isn't appearing, see the vs-textmate-grammar skill for registration steps.

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What NOT to do

Do NOT assume a solution is loaded — in Open Folder mode, IVsSolution reports no projects. Guard against null project references.

Do NOT use ProvideAutoLoad with SolutionExists for Open Folder features — use the Open Folder UI context GUID (4646B819-1AE0-4E79-97F4-8A8176FDD664).

Do NOT block the UI thread in file scanners or context providers — they run during indexing. Always use async Task implementations.

See also

• vs-language-server
• vs-textmate-grammar
• vs-solution-events
• vs-context-menu

Related documentation

• Open Folder extensibility overview
• Workspaces API
• File contexts and actions
• Workspace indexing
• Workspace build support
• Workspace language services
• VSSDK Open Folder sample