makeRelative never introduces "../"

[mgsloan]

This is due to how the implementation in filepath works - https://hackage.haskell.org/package/filepath-1.4.1.0/docs/System-FilePath-Posix.html#v:makeRelative . While somewhat "correct" to never yield "../", I find that behavior fairly useless. We should choose the behavior that will reduce unexpected errorcases in user code. If .. does go up a directory, then it should be used. Otherwise throw some error like "Couldn't make /some/abs/path relative /a/wonky/path because they don't straightforwardly share an ancestor"

[mrkkrp]

AFAIK, it's not possible to construct a Path with .. segment in it anyway, see: commercialhaskell/path#8. For example:

λ> parseRelFile "../something.txt"
*** Exception: InvalidRelFile "../something.txt"