Function diff_attr_external_driver 

pub fn diff_attr_external_driver(
    git_dir: &Path,
    config: &ConfigSet,
    path: &str,
) -> Option<(String, bool)>

Resolved external diff driver from a path’s diff=<name> attribute.

Mirrors Git’s userdiff_find_by_path → drv->external: when a path has a diff=<name> attribute and diff.<name>.command is configured, that driver takes precedence over GIT_EXTERNAL_DIFF / diff.external. The boolean is diff.<name>.trustExitCode.