A challenging architectural problem that several of us are trying to get someone nerdsniped into: inverting the dependency tree, such that you first check what symbols exist in a large crate like windows, then go to all the crates depending on it and see what they actually consume, then go back and only compile the bits needed for those symbols.

That'd be a massive improvement to compilation time, but it's a complicated change. You'd have to either do a two-pass compilation (first to get the symbol list, then again to compile the needed symbols) or leave that instance of the compiler running and feed the list of needed symbols back into it.