Backporting Tickets to a Release Branch¶

So you have a ticket that you think should be backported to a previous release. What next?

First, add the label “backport-v23” to your jira ticket, replacing “23” here and elsewhere on this page with the actual release you’re targeting. To backport to multiple releases, add multiple labels.

This will flag it for review by the DM-CCB. Continue merging your ticket to the default branch (main) and mark the ticket Done per instructions in the normal DM Development Workflow with Git, GitHub, JIRA and Jenkins.
Wait for approval. The ticket will gain the label “backport-approved.” A comment will be posted on the ticket that you may start the backporting process. Backports are approved for all requested releases together.
Checkout the release branch, v23.0.x, for each repo affected by your ticket.
```
git checkout v23.0.x
```
If the repo does not already have a v23.0.x branch, you need to create one based on v23.0.0.rc1 (not the latest rcN, although that should be identical):
```
git checkout v23.0.0.rc1
git checkout -b v23.0.x
git push -u origin v23.0.x
```
Now treat v23.0.x same as you would the default branch (main).
Create a copy of your ticket branch called tickets/DM-XXXXX-v23.
```
git checkout tickets/DM-XXXXX
git checkout -b tickets/DM-XXXXX-v23
git rebase --onto v23.0.x <sha_of_last_commit_before_your_branch>
```
In a new clone, this branch may not exist anymore if you have already merged your PR because merged branches may be automatically deleted. In this case, you can branch tickets/DM-XXXXX-v23 from v23.0.x, and cherry-pick the ticket commits.
```
git checkout v23.0.x
git checkout -b tickets/DM-XXXXX-v23
git cherry-pick <ticket commit>
```
The following may help you find your hash[es] from main: git show --quiet $(git log --oneline | grep 'Merge.*DM-XXXXX' | cut -d' ' -f1)^2
Resolve any rebase or cherry-pick problems depending on your method. Continue using the same procedure outlined in Review Preparation. Check that it cleanly builds via scons. There should be a latest shared v23.0.0.rcN stack on lsst-devl. Run Jenkins. When running Jenkins, build against the release branch and rc1 even if later rcNs exist. The default SPLENV_REF value (the rubin-env conda metapackage version) may no longer be appropriate for v23.0.x. If you are unsure of the recommended env for the release, see the release documentation page, the release tag files. or the env_name files nested under /sdf/group/rubin/sw/tag/ at USDF.
```
REFS: tickets/DM-XXXXX-v23 v23.0.x v23.0.0.rc1
PRODUCTS: lsst_distrib lsst_ci ci_imsim ci_hsc
SPLENV_REF: 0.8.0
```
You may find that the ticket cannot be cleanly backported without first backporting another ticket.
When it passes, merge to v23.0.x using the same procedure outlined in Merging, including creating a pull request. On your pull request, remember to change the base branch to v23.0.x. If the backport was clean, you may self-review. If the backport was not clean and you would like another pair of eyes, you may ask someone to hit the “Approved” button on GitHub, but please do not put your ticket status back into In Review on Jira.
When a ticket has been backported to all requested releases, label your Jira ticket backport-done.