Function explain_package 

pub fn explain_package(
    graph: &PackageGraph,
    roots: &[usize],
    name: &str,
    active_patches: Option<&ActivePatchSet>,
    lockfile: Option<&Lockfile>,
) -> Result<PackageExplanation, ExplainError>

Build a PackageExplanation for name. Returns ExplainError::PackageNotFound when the name is not in the resolved graph; returns ExplainError::AmbiguousPackageName if a future graph gains multiple packages with the same name from distinct sources (today the resolver enforces unique names).

Errors

Returns ExplainError::PackageNotFound (with the known package names as candidates) when no package in graph matches name, and ExplainError::AmbiguousPackageName when more than one package shares that name.