Function resolve_local_datetime 

pub(crate) fn resolve_local_datetime<T: TimeZone>(
    tz: &T,
    local: &NaiveDateTime,
) -> Option<DateTime<T>>

Reads local as a wall clock time in tz, resolving daylight savings ambiguities and gaps as described on resolve_local_offset.

This is TimeZone::from_local_datetime with the two unresolvable LocalResult cases decided rather than rejected.