Suppose we have the following revision graph:
A-B (master) \ C (feature-a) \ D (feature-b) [depends on feature a] \ E (feature-c) [depends on feature b]
And master is then modified to follow with commit
F. <strong>Is there any simple way to rebase
F (master) so that branches
feature-c all end up as follows:</strong>
A-B-F (master) \ C' (feature-a) \ D' (feature-b) \ E' (feature-c)
In real world situations there are obviously multiple patches between each feature so re-attaching branches in-between manually to rebased history is tedious and error prone job. I know that I can rebase
E' with a simple
git checkout feature-c && git rebase master but that leaves branches
feature-b pointing to commits
D instead of
D'. Rebase should have all the info to move all the branches, right?
There's nothing built in to git to do this, but it's certainly script-able.
What you need to do is:
<li>Identify the branch(es) to be rebased (here
feature-c).</li> <li>For each branch, determine which to-be-rebased branches "contain" them (let's call this "is a predecessor"). Branch
Xis a predecessor of
Yis a descendent of the
X(and choose something here to handle/break-ties-with two branch names that identify the same commit). In this case,
feature-ais a predecessor of both
feature-bis a predecessor of
feature-c(only). Save the "distance back" values for predecessors (how far to chase parent chain).</li> <li>Perform a topological sort. (Actually you can cheat and just find leaves. You only need a cycle-check if you pick branch names by some method other than observing the commit DAG.)</li> <li>For each leaf (in this case just
<li>For each predecessor of this leaf, move it from wherever it is now, to N-parents-back from the new leaf tip.</li>
(That's it, all done.)
Predecessor testing is easy with
git merge-base --is-ancestor (pairwise) or
git branch --contains (en masse, but requires filtering away non-rebased branches). Finding the "N back" value is a little trickier, but I believe can be done with
git rev-list piped to
wc -l, for instance.
Edit: I see that the linked answer (in comment above) uses a similar algorithm—including topo-sort/cyclicality-checking, needed because the branch selection method is not "take from commit DAG"—but with more work, explicitly rebasing each branch as directed. If you work from the DAG, the leaf rebase has done all the work, and the predecessors can simply be relabeled, as I noted.
git checkout featurea git rebase git branch --contains (sha1 of your old commit C) |xargs -n 1 git rebase --onto (sha1 of your new commit C') (sha1 of your old commit C)
The best way I can currently think of is rebasing one after the other:
git rebase --onto master B feature-a git rebase --onto feature-a C feature-b git rebase --onto feature-b D feature-c
But whenever you run into a problem like this, please think again, if you really want this and understand the consequences.
It should be simple. Rebasing
F would rabes the whole branch with commits
git checkout B … git commit -m 'F' git checkout E git rebase F