conflicts now generally expects packages that override functions in base packages to obey the “superset principle”, i.e. that
foo::bar(...) must return the same value of
base::bar(...) whenever the input is not an error. In other words, if you override a base function you can only extend the API, not change or reduce it.
There are two exceptions. If the arguments of the two functions are not compatible (i.e. the function in the package doesn’t include all arguments of the base package), conflicts can tell it doesn’t follow the superset principle. Additionally,
dplyr::lag() fails to follow the superset principle, and is marked as a special case (#2).
Functions that have moved between packages (i.e. functions with a call to
.Deprecated("pkg::foo")) as the first element of the function body) will never generate conflicts.