Jamie Tanna documented the often-opaque process for setting up an external command as a `git diff` driver, moving beyond the simpler `textconv` method. Tanna noted that documentation for this capability, which he explored while working on `renovate-packagedata-diff`, is surprisingly hard to locate within Git's manuals. This approach proves necessary when the goal is exposing richer contextual data rather than just text conversion.

Git passes a surprising seven arguments to these external diff tools, offering file paths, SHA-1 hashes, and octal modes for both the 'before' and 'after' states. Understanding these arguments is key; for instance, `/dev/null` appears as the 'before' file when a new file is added, and as the 'after' file upon deletion. This rich input data allows for sophisticated custom tooling.

As a practical demonstration, Tanna provided a wrapper script utilizing oasdiff to generate a human-readable changelog when comparing OpenAPI specification files. This script checks for file addition or deletion states before invoking the specific comparison logic. Caching results using the provided SHA-1 checksums represents a sensible optimization for repeat operations.