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How to Move Mercurial Changesets to a New Branch

Sometimes you put your code in the wrong branch, but catch it in time to fix it

This is me when I realize I've been committing in the wrong branch all day:

via GIPHY

Fortunately, there is a way to move changesets between branches, provided you haven't pushed your changes out to any other repositories. If you have pushed your changes out to the mothership repository, or your coworkers, the only way to pick up the pieces is to get all the users of the repo together and coordinate. That is beyond to scope of this article, and too hard for all but the smallest or dictatorial teams.

Problem Setup

Here at Reci-p.com we make recipes and sell advertising. I've been hard at work writing up new recipes. Here's what I start with:

$ hg history
changeset:  1:b1c330d2ac79
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added quesadilla recipe

changeset:  0:6f5ef8f77a9f
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Jan 28 11:30:00 2017 -0900
summary:    Added taco recipe

I want to add drink recipes, but they aren't ready to show to our valuable users, so I want to add them in a development branch. Unfortunately, I've been out all night sampling drink recipes and I forget to create the new branch!

via GIPHY

This is what I end up with:

$ hg history    
changeset:  3:398dfc004270
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added michela recipe

changeset:  2:852364587134
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added mojito recipe

changeset:  1:b1c330d2ac79
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added quesadilla recipe

changeset:  0:6f5ef8f77a9f
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Jan 28 11:30:00 2017 -0900
summary:    Added taco recipe

Fortunately, before I push all my code to the mothership repo, I notice I've been working in the wrong branch.

Move My Code to a Different Branch

The approach to fixing this problem is to create the missing branch, then create a patch from my new changesets, apply the patch to the new branch, then strip off the changesets from the incorrect branch.

Working in the same repository as above:

$ hg export -o patch.diff 3 2

I create a patch, which shows up as a file called patch.diff.

Create a branch off the newest changeset before I started adding new stuff:

$ hg update 1
$ hg branch drinks
$ hg commit

Patch the new branch I just made:

$ hg import patch.diff

This is dangerous, so make sure you are targeting the correct changeset. You can't easily undo this. You also need to have the strip extension enabled

Remove the changes off the original branch, so we can avoid mixing drink and food recipes:

$ hg strip 3

Phew, my repository is fixed. Now when look at the history I can see that I've got everything in the correct branch:

$ hg history -l 4
changeset:  4:8afca56c4940
branch:     drinks
tag:        tip
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added michela recipe

changeset:  3:357ff9545db
branch:     drinks
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added mojito recipe

changeset:  2:357ff9545db
branch:     drinks
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    drinks branch

changeset:  1:b1c330d2ac79
user:       Gunnar Gissel <gunnar@reci-p.com>
date:       Sat Feb 04 05:15:00 2017 -0900
summary:    Added quesadilla recipe

Now I'm safe to push and I won't accidentally pollute our recipes with drink mixing recipes

via GIPHY

Tags: mercurial hg dvcs version control vcs problem fix til

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