How can I output errors when using .less programmatically?

Question

I\'ve written an ASP.NET MVC action method that receives a .less file name, processes it via Less.Parse() and outputs the processed css file.

Answer 1

I just faced this today in my RequestReduce project. I was getting blank less -> css transforms because there were parse errors that appeared to be going into the ether. Thanks to qes's answer I was able to work out a solution where I could write the errors to the response stream. Here is my dotless.Core.Loggers.ILogger:

public class LessLogger : ILogger
{
    public void Log(LogLevel level, string message)
    {
    }

    public void Info(string message)
    {
    }

    public void Debug(string message)
    {
    }

    public void Warn(string message)
    {
    }

    public void Error(string message)
    {
        Response.Write(message);
    }

    public HttpResponseBase Response { get; set; }
}

I pass this into the Configuration sent to the EngineFactory:

            var engine = new EngineFactory(new DotlessConfiguration
                                               {
                                                   CacheEnabled = false,
                                                   Logger = typeof (LessLogger)
                                               }
                ).GetEngine();

For unit testing purposes I wanted to pass in my HttpResponseBase that would write the error. This is where I felt things getting ugly with some nasty casting to get a reference to my logger:

            ((LessLogger)((LessEngine)((ParameterDecorator)engine).Underlying).Logger).Response = response;

I hope this helps out and if someone knows of a more elegant way to get a reference to the logger, please let me know.