Function parse_index_file 

pub fn parse_index_file(
    object_format: ObjectFormat,
    bytes: &[u8],
) -> Result<LogicalIndex, Error>

Parses one complete raw .git/index byte string under git-index-v1: versions two through four, ordinary stage-zero rows only, the exact mode pairings, strictly increasing prefix-free paths, mandatory unknown or split-index and sparse-directory extensions rejected, and the trailing checksum verified in the declared namespace.

Errors

IndexUnmerged for any nonzero stage, IntentToAdd for that bit, and IndexInvalid for every structural defect.