Enforcing Type-Safe Linking using Inter-Package Relationships

Strongly-typed languages rely on link-time checks to ensure that type safety is not violated at the borders of compilation units. Such checks entail very fine-grained dependencies among compilation units, which are at odds with the implicit assumption of backward compatibility that is relied upon by common library packaging techniques adopted by FOSS (Free and Open Source Software) package-based distributions. As a consequence, package managers are often unable to prevent users to install a set of libraries which cannot be linked together. We discuss how to guarantee link-time compatibility using inter-package relationships; in doing so, we take into account real-life maintainability problems such as support for automatic package rebuild and manageability of ABI (Application Binary Interface) strings by humans. We present the dh_ocaml implementation of the proposed solution, which is currently in use in the Debian distribution to safely deploy more than 300 OCaml-related packages.