Function make_validity_registration 

pub fn make_validity_registration<'a, W: Write, E: Iterator<Item = (&'a StorePathRef<'a>, R)>, R: Iterator<Item = &'a StorePathRef<'a>> + ExactSizeIterator + 'a>(
    w: &mut W,
    elems: E,
) -> Result

Produces the format that Nix calls “makeValidityRegistration” and describes as: “A string accepted by decodeValidPathInfo() that registers the specified paths as valid.” Explained differently, this is the text format used in exportReferencesGraph, in the non-structured attrs case, which can be passed to nix-store --register-validity. We don’t implement the showDerivers and showHash functionality, as that doesn’t seem to be used for exportReferenceGraph.