Function detect_provider_dependency_cycles 

pub fn detect_provider_dependency_cycles(
    providers: &HashMap<String, ProviderDecl>,
    errors: &mut Vec<CompileError>,
)

v0.12: detect cycles in the provider dependency graph. Each provided capability depends (via its provider’s given) on other capabilities; a cycle means the composition root cannot order instantiation. Emits bynk.provider.dependency_cycle on every provider that participates in a cycle. providers is keyed by capability name.