membranedepends

Membranedepends is a software library and concept primarily associated with the Nix package manager and its ecosystem. It provides a mechanism for managing dependencies within Nix derivations that are based on files or directories residing within a Nix store path. Essentially, it allows Nix to track not just direct build-time dependencies, but also implicit dependencies that are discovered or used during the execution of a derivation's build process, particularly those that are accessed through a mounted filesystem structure.

The core idea behind membranedepends is to ensure that when a Nix derivation is built, all the necessary components it might access via its build environment are correctly staged and available. This is crucial for reproducible builds. If a derivation relies on a file or directory that isn't explicitly listed as an input, Nix might not know to include it, leading to build failures or, worse, irreproducible builds if the missing dependency is present on the build machine but not in the Nix store. Membranedepends helps capture these "runtime" dependencies that manifest during the build phase.

This is often achieved by intercepting filesystem access calls within a sandboxed build environment. When a derivation attempts to read from or write to a file or directory that originates from another Nix store path, membranedepends records this access. This information is then used to ensure that the relevant Nix store path is added as a dependency to the current derivation. This allows Nix to accurately represent the complete set of inputs required for a reproducible build, preventing silent failures or inconsistencies.