Hello, 

I have tried to implement something like dynamic bundling. The idea is that on one page I might have different blocks and each of them to require different script files. I want to combine them in one bundle, which is page specific. What I have implemented: 

public static void AddScriptFileToPageBundle(this HtmlHelper htmlHelper, string scriptUrl)
{
      AddFileToPageBundle(BundleType.Script, scriptUrl);
}

private static void AddFileToPageBundle(BundleType bundleType, string fileUrl)
        {
            string templateName = bundleType == BundleType.Script ? ScriptsPageBundleTemplate : StylesCssPageBundleTemplate;
            string bundleVirtualPath = String.Format(templateName, HttpContext.Current.Request.Path);

            // Remove trailing slash if exists
            if (bundleVirtualPath.EndsWith("/"))
                bundleVirtualPath = bundleVirtualPath.Substring(0, bundleVirtualPath.Length - 1);

            var bundle = BundleTable.Bundles.GetBundleFor(bundleVirtualPath);
            if (bundle != null)
            {
                bundle.Include(fileUrl);
            }
            else
            {
                // File URL must start with ~, otherwise is not found
                if (!fileUrl.StartsWith("~"))
                    fileUrl = "~" + fileUrl;

                if (bundleType == BundleType.Script)
                {
                    var pageBundle = new CustomScriptBundle(bundleVirtualPath);
                    pageBundle.Include(fileUrl);
                    pageBundle.Transforms.Add(new ScriptTransformer(new MicrosoftAjaxJsMinifier()));
                    pageBundle.Orderer = new NullOrderer();
                    BundleTable.Bundles.Add(pageBundle);
                }
                else 
                {
                    var pageBundle = new CustomStyleBundle(bundleVirtualPath);
                    pageBundle.Include(fileUrl);                    
                    pageBundle.Transforms.Add(new StyleTransformer(new MicrosoftAjaxCssMinifier()));
                    pageBundle.Orderer = new NullOrderer();
                    BundleTable.Bundles.Add(pageBundle);
                }
            }
        }

Then in everyblock, which requires custom scripts, I have the following

@{
    Html.AddScriptFileToPageBundle("~/Static/Scripts/Blocks/CookieWarningBlock/CookieWarningBlock.js");
}

I combine all page specific scripts. Then, I have another method: 

public static MvcHtmlString RenderScriptsPageBundle(this HtmlHelper htmlHelper)
        {
            return RenderPageBundle(BundleType.Script);
        }

private static MvcHtmlString RenderPageBundle(BundleType bundleType)
        {
            string templateName = bundleType == BundleType.Script ? ScriptsPageBundleTemplate : StylesCssPageBundleTemplate;
            string bundleVirtualPath = String.Format(templateName, HttpContext.Current.Request.Path);

            // Remove trailing slash if exists
            if (bundleVirtualPath.EndsWith("/"))
                bundleVirtualPath = bundleVirtualPath.Substring(0, bundleVirtualPath.Length - 1);

            var bundle = BundleTable.Bundles.GetBundleFor(bundleVirtualPath);
            if (bundle != null)
            {
                string bundleUrl = BundleTable.Bundles.ResolveBundleUrl(bundleVirtualPath, true);
                string result = bundleType == BundleType.Script ?
                    String.Format("", bundleUrl) :
                    String.Format("", bundleUrl);

                return MvcHtmlString.Create(result);
            }

            return MvcHtmlString.Empty;
        } 

and in the _Root.cshtml I invoke it

@Html.RenderScriptsPageBundle()

At the end on every page I have the following result 

Homepage: 

Our-Products:

... and so on for the rest of the pages. As you can see, I am using the page request path as a unique bundle identifier. It all worked well in our dev & test environments. However, when we deployed to production I started getting the following error:

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.List`1.Enumerator.MoveNextRare()
   at System.Web.Optimization.Bundle.EnumerateFiles(BundleContext context)
   at System.Web.Optimization.Bundle.GenerateBundleResponse(BundleContext context)
   at System.Web.Optimization.Bundle.GetBundleUrl(BundleContext context, Boolean includeContentHash)
   at MyCompany.Web.Core.Business.Extensions.HtmlHelperExtensions.RenderPageBundle(BundleType bundleType) in c:\1250\489\Sources\WEB\Main\Web_dev\MyCompany.Web.Main.Site\MyCompany.Web.Core\Business\Extensions\HtmlHelperExtensions.cs:line 189
   at ASP._Page_Views_Shared_Layouts__Root_cshtml.Execute() in e:\Sites\CompanyWebsite\Views\Shared\Layouts\_Root.cshtml:line 35

Another weird thing: this is reproducible only if I copy and paste the link (for example the homepage) in a new browser tab and it happens randomly. If have the site already opened, and I click on the logo or other link pointing to the homepage, it is not reproducible.  

I would appreaciate any help on this. Thank you in advance.