Error List integration

The Error List is one of Visual Studio’s most prominent tool windows. Extensions can push custom errors, warnings, and messages into it using the toolkit’s TableDataSource and ErrorListItem classes - no raw ITableDataSource or ITableEntry implementation needed.

Create a TableDataSource

The TableDataSource is the bridge between your extension and the Error List. Create one and give it a unique name (typically your extension name).

TableDataSource _errorList = new TableDataSource("MyExtension");

You only need one instance per extension. It’s common to create it once in your package or a singleton helper class.

Add errors to the Error List

Create ErrorListItem objects and pass them to AddErrors. Each item needs at least a FileName and a Message.

var errors = new List<ErrorListItem>
{
    new ErrorListItem
    {
        ProjectName = "MyProject",
        FileName = @"C:\repos\MyProject\Program.cs",
        Line = 10,
        Column = 5,
        Message = "Missing semicolon",
        ErrorCode = "EXT001",
        Severity = __VSERRORCATEGORY.EC_ERROR,
        BuildTool = "MyExtension"
    },
    new ErrorListItem
    {
        ProjectName = "MyProject",
        FileName = @"C:\repos\MyProject\Program.cs",
        Line = 25,
        Message = "Unused variable 'x'",
        ErrorCode = "EXT002",
        Severity = __VSERRORCATEGORY.EC_WARNING,
        BuildTool = "MyExtension"
    }
};

_errorList.AddErrors(errors);

The Severity property controls the icon and how the item shows up when filtering the Error List:

• __VSERRORCATEGORY.EC_ERROR - Error (red)
• __VSERRORCATEGORY.EC_WARNING - Warning (yellow)
• __VSERRORCATEGORY.EC_MESSAGE - Message (blue)

Tip: Setting the Line and Column properties makes the entry clickable - double-clicking navigates to that location in the editor.

Clear errors

Remove all previously added errors when they are no longer relevant (for example, after a successful re-validation).

_errorList.CleanAllErrors();

Putting it all together

Here’s a typical pattern where errors are refreshed every time a document is saved:

[Command(PackageIds.ValidateCommand)]
internal sealed class ValidateCommand : BaseCommand<ValidateCommand>
{
    private static readonly TableDataSource _errorList = new("MyExtension");

    protected override async Task InitializeCompletedAsync()
    {
        VS.Events.DocumentEvents.Saved += OnDocumentSaved;
    }

    private void OnDocumentSaved(string filePath)
    {
        _errorList.CleanAllErrors();

        IEnumerable<ErrorListItem> errors = ValidateFile(filePath);
        _errorList.AddErrors(errors);
    }

    private static IEnumerable<ErrorListItem> ValidateFile(string filePath)
    {
        // Your validation logic here
        yield break;
    }

    protected override Task ExecuteAsync(OleMenuCmdEventArgs e)
    {
        return Task.CompletedTask;
    }
}

ErrorListItem properties

ProjectName (string) - Project name shown in the Error List.

FileName (string) - Full path to the file. Required for clickable navigation.

Line (int) - 0-based line number.

Column (int) - 0-based column number.

Message (string) - The error/warning message text.

ErrorCode (string) - Short error code (e.g. “EXT001”).

ErrorCodeToolTip (string) - Tooltip shown when hovering the error code.

ErrorCategory (string) - Category string.

Severity (__VSERRORCATEGORY) - Error, Warning, or Message.

HelpLink (string) - URL for the help link.

BuildTool (string) - Name of the tool that generated the error.

Icon (ImageMoniker) - Custom icon moniker.