pub fn from_package_ids<'a>(
        graph: &PackageGraph,
        package_ids: impl IntoIterator<Item = &'a PackageId>,
    ) -> Result<Self, Error> {
        let summary_ids = package_ids
            .into_iter()
            .map(|package_id| Ok(graph.metadata(package_id)?.to_summary_id()))
            .collect::<Result<_, Error>>()?;
        Ok(PackageSetSummary {
            summary_ids,
            ..PackageSetSummary::default()
        })
    }
Constructs a `PackageSetSummary` from an iterator of [`PackageId`]s.
guppy/src/graph/summaries/package_set.rs