Function hg::dagops::heads

pub fn heads<'a>(
    graph: &impl Graph, 
    iter_revs: impl Clone + Iterator<Item = &'a Revision>
) -> Result<HashSet<Revision>, GraphError>

Relative heads out of some revisions, passed as an iterator.

These heads are defined as those revisions that have no children among those emitted by the iterator.

Performance notes

Internally, this clones the iterator, and builds a HashSet out of it.

This function takes an Iterator instead of impl IntoIterator to guarantee that cloning the iterator doesn't result in cloning the full construct it comes from.