The ability to do this based on file modifications is my favorite feature of the build tool SBT (a Java/Scala build tool). I really wish more build tools would

The ability to do this based on file modifications is my favorite feature of the build tool SBT (a Java/Scala build tool). I really wish more build tools would integrate this natively. Usually this functionality only shows up as a plugin for a specific build task (such a Spork for Rails testing) or as a platform specific command line hack (which isn't as useful if the build tool has a large start up time).