Here's some thinking outside the box. Traditional compilers are focused on building an executable as fast as possible, throwing away an enormous amount of state each time. The new rustc incremental compilation attempts to re-use some of that computed state, although still early days. If however the compiler's state remains persistent (it is running as a daemon) then small code changes should usually be pretty fast - it's analogous to the code scanners of Eclipse. If the target of the compiler isn't a native executable, but a continuously updated image containing code, then the link gets pretty fast as well. The result will not be fast, but it will be _fast enough_ to test changes.