This is an addition to (and sub-warning of) -Wnullability-completeness that warns when an array parameter is missing nullability. When the specific warning is switched off, the compiler falls back to only warning on pointer types written as pointer types.
Note that use of nullability within an array triggers the completeness checks regardless of whether or not the array-specific warning is enabled; the intent there is simply to determine whether a particular header is trying to be nullability-aware at all.
Depends on D25850. Part of rdar://problem/25846421.