Function debug_adjacent_by 

pub fn debug_adjacent_by<T: Debug, F: Fn(&T, &T) -> bool>(
    items: &[T],
    is_adjacent: F,
) -> DebugAdjacentBy<'_, T, F>

Returns a value that implements Debug by collapsing runs of “adjacent” items.

The is_adjacent parameter defines whether two values in T are adjacent.