c# - Roslyn Code Action: How to check if preview or real execution?

Question

I am currently experimenting with Roslyn and Code Actions, more specific Code Refactorings. It feels kind of easy, but I have a difficulty I cannot solve.

Code actions are executed once against a dummy workspace as a "preview" option, so that you can see the actual changes before you click the action and execute it against the real workspace.

Now I am dealing with some things Roslyn can't really do (yet), so I am doing some changes via EnvDTE. I know, it's bad, but I couldn't find another way.

So the issue here is: When I hover over my code action, the code gets executed as preview, and it should NOT do the EnvDTE changes. Those should only be done when the real execute happens.

I have created a gist with a small example of my code. It doesn't really makes sense, but should show what I want to achieve. Do some modifications via roslyn, then do something via EnvDTE, like changing Cursor position. But of course only on the real execution.

The relevant part for those who can't click the gist:

public sealed override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
{
    var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(continueOnCapturedContext: false);
    var node = root.FindNode(context.Span);

    var dec = node as MethodDeclarationSyntax;
    if (dec == null)
        return;

    context.RegisterRefactoring(CodeAction.Create("MyAction", c => DoMyAction(context.Document, dec, c)));
}

private static async Task<Solution> DoMyAction(Document document, MethodDeclarationSyntax method, CancellationToken cancellationToken)
{
    var syntaxTree = await document.GetSyntaxTreeAsync(cancellationToken);
    var root = await syntaxTree.GetRootAsync(cancellationToken);

    // some - for the question irrelevant - roslyn changes, like:
    document = document.WithSyntaxRoot(root.ReplaceNode(method, method.WithIdentifier(SyntaxFactory.ParseToken(method.Identifier.Text + "Suffix"))));

    // now the DTE magic
    var preview = false; // <--- TODO: How to check if I am in preview here?
    if (!preview)
    {
        var requestedItem = DTE.Solution.FindProjectItem(document.FilePath);
        var window = requestedItem.Open(Constants.vsViewKindCode);
        window.Activate();

        var position = method.Identifier.GetLocation().GetLineSpan().EndLinePosition;
        var textSelection = (TextSelection) window.Document.Selection;
        textSelection.MoveTo(position.Line, position.Character);
    }

    return document.Project.Solution;
}

Answer 1

You can choose to override ComputePreviewOperationsAsync to have different behavior for Previews from regular code.