[kmike84]

The API is quite simple - you need to implement a script which takes 3 arguments, writes a result of a merge to a file, and exits with non-zero status code in case of merge error. Quote from https://git-scm.com/docs/gitattributes#_defining_a_custom_me...:

To define a custom merge driver filfre, add a section to your $GIT_DIR/config file (or $HOME/.gitconfig file) like this

  [merge "filfre"]
    name = feel-free merge driver
    driver = filfre %O %A %B %L %P
    recursive = binary

The merge.?.name variable gives the driver a human-readable name.

The merge.?.driver variable’s value is used to construct a command to run to merge ancestor’s version (%O), current version (%A) and the other branches' version (%B). These three tokens are replaced with the names of temporary files that hold the contents of these versions when the command line is built. Additionally, %L will be replaced with the conflict marker size (see below).

The merge driver is expected to leave the result of the merge in the file named with %A by overwriting it, and exit with zero status if it managed to merge them cleanly, or non-zero if there were conflicts.