Function resolve_dependency_graph 

pub async fn resolve_dependency_graph(
    root_id: &PackageId,
    root: &PackageInfo,
    source: &dyn Source,
) -> Result<DependencyGraph, ResolveError>

Given the PackageInfo for a root package, discover its dependency graph.

Unlike resolve(), this only queries and links packages. It does not apply runtime compatibility checks such as rejecting duplicate package versions.