The checkout subcommand replaces the symlink that normally points at a
file's content, with a copy of the file. Once you've checked a file out,
you can edit it, and git commit it. On commit, git-annex will detect
if the file has been changed, and if it has, add its content to the
annex.
Internally, this will need to store the original symlink to the file, in
.git/annex/checkedout/$filename.
- git-annex uncheckout moves that back
- git-annex pre-commit hook checks each file being committed to see if it has a symlink there, and if so, removes the symlink and adds the new content to the annex.
And it seems the file content should be copied, not moved or hard linked:
- Makes sure other annexes can find it if transferring it from this annex.
- Ensures it's always available for uncheckout.
- Avoids the last copy of a file's content being lost when the checked out file is modified.