Hacking the ASP.NET Parser

A while ago I blogged about using external templates in an asp.net application. The problem with that was it wasn’t natively supported, so I had to create a derived SpecialRepeater in order to take advantage of the external template system. In this latest parser hack I’ve managed to “trick” the asp.net parser into letting me declaratively set any template property to be a virtual path in order to load a user control into that template at runtime. The ASP.NET compliation system is pretty complex. There are all kinds of extensibility points, including BuildProviders, PageParserFilters, ControlBuilders, ExpressionBuilders and the list goes on. One unknown *feature* of the parser is it’s ability to generate code from something called an InstanceDescriptor.