How to conditionally skip compilation

As I mentioned in my last post, I was having problems getting an MVC web application to play nice with my framework targeting builds. Specifically, my CI server would fall over if I tried to build using Framework 3.5 when the web application was using 4.0 (due to 4.0-specific web.config settings that 3.5 does not recognise). I managed to spend a large portion of the afternoon searching for an answer until I had one of those “eureka” moments. My objective was to simply not build the web application unless the framework was 4.0 (the same would apply to any project that is framework version-specific). I tried putting a conditional on the project element. No Joy. I tried a whole bunch of other things and it was starting to look like I would have to manually configure each project to be built – very nasty, not at all what I want.

My “eureka” moment happened as I was gazing forlornly at a project file. My eye alighted upon an attribute of DefaultTargets="Build" on the project element. Build? I thought… I’ve not seen a target called that. A quick check confirmed my suspicion. The “Build” target is effectively inherited. In a flash I thought I wonder if I can intercept this? I changed the attribute to DefaultTargets="Conditional" and then added the following target and all is well again in Narnia:

<Target Name="Conditional">
<CallTarget Targets="Build" Condition=" '$(TargetFrameworkVersion)' == 'v4.0' " />
</Target>