Function write_patch 

pub fn write_patch<W: Write>(
    repo: &Repository,
    entries: &[DiffEntry],
    opts: &PatchTextOptions,
    out: &mut W,
) -> Result<()>

Write git diff --binary-style patches for tree diff entries (for git apply).

Emits diff --git headers, index lines, unified hunks or GIT binary patch bodies.

Errors

Propagates ODB reads, diff generation, and I/O errors.