I don't think you've done anything incorrectly. Though I would approach it using the IBundleBuilder interface, as this will also keep regular comments out of production from prying eyes who switch user agent, like specified in How to prevent User-Agent: Eureka/1 to return source code. I show some steps on how to test against this in this related blog post.
public class ConfigurableStyleBuilder : IBundleBuilder
{
public virtual string BuildBundleContent(Bundle bundle, BundleContext context, IEnumerable<BundleFile> files)
{
var content = new StringBuilder();
foreach (var file in files)
{
FileInfo f = new FileInfo(HttpContext.Current.Server.MapPath(file.VirtualFile.VirtualPath));
CssSettings settings = new CssSettings();
settings.CommentMode = Microsoft.Ajax.Utilities.CssComment.Important;
var minifier = new Microsoft.Ajax.Utilities.Minifier();
string readFile = Read(f);
string res = minifier.MinifyStyleSheet(readFile, settings);
if (minifier.ErrorList.Count > 0)
{
res = PrependErrors(readFile, minifier.ErrorList);
content.Insert(0, res);
}
else
{
content.Append(res);
}
}
return content.ToString();
}
private string PrependErrors(string file, ICollection<ContextError> errors )
{
var content = new StringBuilder();
content.Append("/* ");
content.Append("CSS MinifyError").Append("\r\n");
foreach (object current in errors)
{
content.Append(current.ToString()).Append("\r\n");
}
content.Append("Minify Error */\r\n");
content.Append(file);
return content.ToString();
}
private string Read(FileInfo file)
{
using (var r = file.OpenText())
{
return r.ReadToEnd();
}
}
}
public class BundleConfig
{
public static void RegisterBundles(BundleCollection bundles)
{
var cssBundle = new ConfigurableStyleBundle("~/Content/css");
cssBundle.Include("~/Content/stylesheet1.css");
cssBundle.Include("~/Content/stylesheet2.css");
bundles.Add(cssBundle);
//etc
}
}
I made a NuGet package for this (including a version for scripts) - https://www.nuget.org/packages/LicensedBundler/