Git: maintaining many topic branches on a frequently-moving base

Question

In my day-to-day git workflow, I have many topic branches, like so:

              o--o--o (t2)
             /
         o--o (t1)
        /
 o--o--o (master)
        \
         o--o--o (t3)

When I pull from upstream,

              o--o--o (t2)
             /
         o--o (t1)
        /
 o--o--o--n--n--n (master)
        \
         o--o--o (t3)

I want to rebase all my topic branches on top of the new master:

                        o'--o'--o' (t2)
                       /
                  o'--o' (t1)
                 /
 o--o--o--n--n--n (master)
                 \
                  o'--o'--o' (t3)

Currently I do this by hand, using git rebase --onto. In this scenario, the whole update process would be:

$ git checkout master
$ git pull
$ git rebase master t1
$ git rebase --onto t1 t2~3 t2
$ git rebase master t3

This gets even hairier when jumping between various topic branches and adding commits.

Dependencies between topic branches in my case are purely tree-like: no branch depends on more than a single other branch. (I have to eventually upstream dependent patches in some particular order, so I choose that order a priori.)

Are there any tools that can help me manage this workflow? I've seen TopGit, but it seems to be tied quite heavily to the tg patch email-based workflow, which isn't relevant to me.

Answer 1

Pretty much the same question was asked on the git mailing list: Rebasing Multiple branches at once... The linked response has a perl script attached that generates the commands you would need.

If you want this script to be fast and avoid having it tread on your toes, also consider using git-new-workdir to set up a working copy just for automatic rebasing.

If you find yourself resolving the same conflicts over and over, consider enabling git rerere.

Having said all that, here is an alternate recipe:

# Construct a placeholder commit that has all topics as parent.
HEADS="$(git for-each-ref refs/heads/\*)" &&
MAGIC_COMMIT=$(echo "Magic Octopus"$'\n\n'"$HEADS" |
  git commit-tree \
    $(git merge-base $(echo "$HEADS" | sed 's/ .*//' ))^{tree} \
    $(echo "$HEADS" | sed 's/ .*//;s/^/-p /')) &&
git update-ref refs/hidden/all $MAGIC_COMMIT

# Rebase the whole lot at once.
git rebase --preserve-merges master refs/hidden/all

# Resolve conflicts and all that jazz.

# Update topic refs from the rebased placeholder.
PARENT=
echo "$HEADS" |
while read HASH TYPE REF
do
  let ++PARENT
  git update-ref -m 'Mass rebase' "$REF" refs/hidden/all^$PARENT "$HASH"
done