Could not think of a foolproof way to detect if the old adjusted branch was
just behind the current branch. It's possible that the user amended the
adjusting commit at the head of the adjusted branch, for example.
I decided to bail in this situation, instead of just entering the old
branch, so that if git annex adjust succeeds the user is always in a
*current* adjusted branch, not some old and out of date one.
What could perhaps be done is enter the old branch and then update it. But
that seems too magical; the user may have rebased master or something or
may not want to propigate the changes from the old branch. Best to error
out.
When git-annex is used with a git version older than 2.2.0, disable support for
adjusted branches, since GIT_COMMON_DIR is needed to update them and was first
added in that version of git.
"git annex adjust" may be a temporary interface, but works for a proof of
concept.
It is pretty fast at creating the adjusted branch. The main overhead is
injecting pointer files. It might be worth optimising that by reusing the
symlink target as the pointer file content. When I tried to do that,
the problem was that the clean filter doesn't use that same format, and so
git thought files had changed. Could be dealt with, perhaps make the clean
filter use symlink format for pointer files when on an adjusted branch?
But the real overhead is in checking out the branch, when git runs the
smudge filter once per file. That is perhaps too slow to be usable,
although it may only affect initial checkout of the branch, and not
updates. TBD.
