Backporting

General

We backport important fixes and improvements from the current master release to get them to our users faster.

Process

We mostly consider bug fixes for backporting. Occasionally, important changes to the API can be backported to make it easier for developers to keep their apps working between major releases. If you think a pull request (PR) is relevant for the stable release, go through these steps:

  1. Make sure the PR is merged to master

  2. Ask the feature maintainer if the code should be backported and add the label backport-request to the PR

  3. If the maintainer agrees, create a new branch based on the respective stable branch, cherry-pick the needed commits to that branch and create a PR on GitHub.

  4. Specify the corresponding milestone for that series to this PR and reference the original PR in there. This enables the QA team to find the backported items for testing and having the original PR with detailed description linked.

Before each patch release there is a freeze to be able to test everything as a whole without pulling in new changes. While this freeze is active a backport isn’t allowed and has to wait for the next patch release.

The QA team will try to reproduce all the issues with the X.Y.Z-next-maintenance milestone on the relevant release and verify it is fixed by the patch release (and doesn’t cause new problems). Once the patch release is out, the post-fix -next-maintenance is removed and a new -next-maintenance milestone is created for that series.

Backporting Steps

Because pushing directly to particular ownCloud branches is forbidden (e.g., origin/stable-xx), you need to create your own remote branch, based off of the branch that you wish to backport to. However, doing so can involve a number of manual steps. To reduce the effort and time involved, use the script below instead.

Backporting Notes

The script relies on a recent version of grep. macOS users may find on their system a version provided from Apple which is outdated and lacking needed options. Use homebrew to install a recent version of grep.
The script uses curl and the jq (lightweight and flexible command-line JSON processor) package. Please install them before first usage. Please see this link for installation details of jq covering various OS.
This script uses the github API. For unauthenticated requests, the rate limit allows for up to 60 requests per hour. Unauthenticated requests are associated with the originating IP address, and not the user making requests. Please see this link for more information about github rate limiting.
The script requires that you have checked out the branch containing the merge SHA1 hash. The script will not proceed if either the merge SHA1 hash is not present or the branch containing the merge SHA1 hash is not checked out.
In case of conflicts, the script exits. The merge conflicts will need to be resolved before manually continuing the backport. When done, we suggest that you use the printed subject title from the script for the Pull Request.
While adding, renaming or changing files has no issues for backporting, the script will fail if files have been deleted. You need to manually finalize the backport using git commands.

Backporting Script

#!/bin/bash
# version 2021.07.31

if ! [ -x "$(command -v jq)" ]; then
  echo
  echo 'Error: jq is not installed.' >&2
  echo 'Please install package "jq" before using this script'
  echo
  exit 1
fi

if ! [ -x "$(command -v curl)" ]; then
  echo
  echo 'Error: curl is not installed.' >&2
  echo 'Please install package "curl" before using this script'
  echo
  exit 1
fi

if [ "$#" -lt 2 ]; then
  echo
  echo "Illegal number of parameters"
  echo "  $0 <merge/commit-sha> <targetBranchName>"
  echo "  For example: $0 1234567 10.8"
  echo
  exit 1
fi

commit=$1
targetBranch=$2
sourceBranch=$(git rev-parse --abbrev-ref HEAD)

# check if the target branch exists on remote to avoid backporting to a non existing remote branch
exists_in_remote=$(git ls-remote --heads origin ${targetBranch})
if [ -z "$exists_in_remote" ]; then
    echo
    echo "Branch $targetBranch does not exist on remote. Create it first. Exiting"
    echo
    exit 1
fi

# check if the target branch already exists locally
exists_in_local=$(git branch --list ${targetBranch})
if [ -z "$exists_in_local" ]; then
    echo
    echo "Branch $targetBranch does not exist locally. Make it available first. Exiting"
    echo
    exit 1
fi

# check if the given merge commit exists in the actual checked out branch
is_merged=$(git branch --contains $1 2>/dev/null | grep -oP '(?<=\*).*')
if [ -z "$is_merged" ]; then
    echo
    echo "$commit does not exist because:"
    echo "- the PR has not been merged yet or"
    echo "- your actual backporting base branch ${sourceBranch} is not pulled/rebased."
    echo "Exiting"
    echo
    exit 1
fi

# get the PR number from the merge commit
# there can be a PR reference text in the commit like "fixes #1234".
# we only need to take the last line which is then the real PR # the commit belongs to
pullId=$(git log $1^! --oneline 2>/dev/null | tail -n 3 | grep -oP '(?<=#)[0-9]*' | tail -n 1)

# get the repository from the given commit
# remove prefix and suffix from the full url returned
repository=$(git config --get remote.origin.url 2>/dev/null)
repository=${repository#"https://github.com/"}
repository=${repository%".git"}

# get the list of commits in PR without any merge commit
# $1^ means the first parent of the merge commit (that is passed in as $1).
# because $1 is a "magically-generated" merge commit, it happily "jumps back"
# to the point on the main branch just before where the PR was merged.
# the commits from that point are exactly the list of individual
# commits in the original PR.
# --no-merges leaves out the merge commit itself, and we get just what we want
commitList=$(git log --no-merges --reverse --format=format:%h $1^..$1)

# get the request reset time window from github in epoch
rateLimitReset=$(curl -iks https://api.github.com/users/zen 2>&1 | grep -im1 'X-Ratelimit-Reset:' | grep -o '[[:digit:]]*')

# get the remaining requests in window from github
rateLimitRemaining=$(curl -iks https://api.github.com/users/zen 2>&1 | grep -im1 'X-Ratelimit-Remaining:' | grep -o '[[:digit:]]*')

# time remaining in epoch
now=$(date +%s)
((remaining=rateLimitReset-now))

# time remaining in HMS
remaining=$(date -u -d @$remaining +%H:%M:%S)

# echo one time for a good rendering
echo

# check if there are commits to cherry pick and list them if present
if [[ -z "$commitList" ]]; then
  echo "There are no commit(s) to cherry pick. Exiting"
  echo
  exit 1
else
  lineCount=$(echo "$commitList" | grep '' | wc -l)
  echo "$lineCount commit(s) to be cherry picked:"
  echo
  echo "$commitList"
  echo
fi

if [ $rateLimitRemaining -le 0 ]; then
  # do not continue if there are no remaining github requests available
  echo
  echo "You do not have enough github requests available to backport"
  echo "The current rate limit window resets in $remaining"
  echo
  exit 1
else
  # get the PR title, this is the only automated valid way to get the title
  pullTitle=$(curl https://api.github.com/repos/$repository/pulls/$pullId 2>/dev/null | jq '.title' | sed 's/^.//' | sed 's/.$//')
  # remove possible line breaks on any location in the string
  pullTitle=${pullTitle//$'\n'/}
fi

# build variables for later use
newBranch="${targetBranch}-${commit}-${pullId}"
message="[${targetBranch}] [PR ${pullId}] ${pullTitle}"

# first check, if the source branch is clean and has no uncommited changes
# in case this is true, checkout does not succeed and nothing needs to be done/switched
# xargs removes any possible leading and trailing whitespaces
is_source_branch_clean=$(git status --porcelain=v1 2>/dev/null | xargs)
if [[ ! -z "$is_source_branch_clean" ]]; then
  echo "Source branch $sourceBranch has probably uncommitted changes. Aborting."
  echo
  exit 1
fi

# exit the script if any statement returns a non-true return value
# means that all commands from now on must run successfully
set -e

# fetch branches and/or tags from one or more other repositories, along with the
# objects necessary to complete their histories
git fetch -p --quiet

# checkout and rebase the target branch
git checkout "$targetBranch" --quiet

# if everything is ok, then rebase the target branch
git pull --rebase --quiet

# create a new branch based on the target branch
# the new branch name equals the new commit name
git checkout -b "$newBranch" "$targetBranch"

echo

# cherry pick all commits from commitList
lC=1
echo "$commitList" | while IFS= read -r line; do
  # start cherry-picking
  echo "Cherry picking commit $lC: $line"

  # check if the commit to be cherry picked is already in the branch
  # this only works if the commit was cherry picked before!
  # else it will just try and continue.
  is_cherry_picked=$(git log --grep $line 2>/dev/null)
  if [[ ! -z "$is_cherry_picked" ]]; then
    echo
    echo "Commit $line has aready been cherry picked, abort backporting."
    # go back to the base branch and delete the new branch with all its contents.
    git checkout --quiet "$sourceBranch"
    git branch -D --quiet $newBranch
    echo
    exit 1
  fi

  # if you do not want to use a default conflict resolution to take theirs
  # (help fix missing cherry picked commits or file renames)
  #git cherry-pick $line > /dev/null
  git cherry-pick -Xtheirs $line > /dev/null
  lC=$(( $lC + 1 ))
done

echo

# the first amend creates the PR headline text
# the second amend creates the PR message text
git commit --quiet --amend -m "$message" -m "Backport of PR #$pullId"

echo "Pushing: $message"
echo

git push --quiet -u origin "$newBranch"
git checkout --quiet "$sourceBranch"
It is highly recommended to use the merge SHA1 hash when backporting a Pull Request. The merge commit includes all PR sub commits to be backported. With that, no individual sub commit backporting is necessary.

The following example assumes that:

  • You save the script in a file called <path>/backport.sh and marked it executable

  • You have checked out the branch containing the merge SHA1 hash (like master)

  • Your Pull Request merge SHA1 hash = 1234567 and your target branch = stable10

The command to backport this Pull Request would be called as follows:

<path>/backport.sh 1234567 stable10
4 commits beeing cherry picked:

2e03d938
fef19729
61ac3f09
0528601f
...
Switched to a new branch ‘stable10-1234567-34654‘
...
[stable10] [PR 34654] Each generated birthday or death event gets a new UID
...
Cherry picking commit 1: 2e03d938
Cherry picking commit 1: fef19729
...
Pushing: ...
...
Please keep in mind that this is an example and you have to adapt the commit hash and the target branch accordingly.

The script lists quantity and commits to be backported and the current commit in process. This can be helpful in case there is a conflict and you manually continue after the conflict has been resolved.

When the script completes, go to GitHub, where it will suggest that you make a PR from pushed branch. Even the script tries to automate, you may need to set the Pull Request subject and message text manually via copy/paste.

Change the base branch to be committed against, from master to your target branch (in our example stable10) and continue.

In case you have installed the xdg-utils package, you can add at the end of the script above following code which opens the PR to be finalized in your browser. macOS does not need this package. Use the command open instead of xdg-open:

# open the browser and prepare the pull request
echo "Creating pull request for branch $targetBranch in $repository"
xdg-open "https://github.com/$repository/pull/new/$targetBranch...$newBranch" &>/dev/null
This command opens the Pull Request and sets the target branch (in our example stable10) for the backport automatically.

Backporting Alias

You can also create a git alias for backporting, making it simpler to use.

Open the ~/.gitconfig file with the editor of your choice and add the following:

[alias]
	backport = !bash -c '<path_to_script>/backport.sh $1 $2' -

Create a backport by invoking following command

git backport 1234567 stable10
Please keep in mind that this is an example and you have to adapt the commit hash and the target branch accordingly.