Would it be feasible (for users wanting reproducible builds) to stick to clean build and sort sources?
Building from scratch sounds very feasible, sorting sources might depend on the build tool but is hopefully easier to hack than fixing Scalac?
IIUC, if stability is source-feature dependent, it’s only tested on compiler and library—which in turn are somewhat conservative/rely on more solid features than maybe shapeless or more original libraries. Of course that’s likely good enough for 90% of the code out there.
What about testing build stability on the community build, once known bugs are squashed?