This page documents decisions we made while finding out how to best work with Git as well and various quality-of-life tips related to Git.

Cloning the Sling git repositories

This is documented in the Sling Aggregator Github module.


Force pushing to the master branch, or to other branches that are shared with others, is discouraged. It makes collaboration harder and potentially impacts other tools as well - Jenkins, SonarCloud, etc. If you need time experimenting and fiddling with history, it's better to start working with an individual repository and then bring it to Sling, once it's stable.

Merging pull requests from contributors

Maintaining a linear history in git is preferred, especially for small contributions. Each commit should be buildable and correct by itself, as much as possible. This is beneficial when reviewing history for changes and also when running git bisect .

In practice, we have found that:

  • for contributions which require no additional fixes we should use the 'Rebase and merge' workflow
  • for contributions which require fixes
    • in case of a single logical commit we should use the 'Squash and merge' workflow to create a single commit. This creates a fast-forward merge, so no merge commit.
    • in case of multiple separate commits we should ask the reviewer to amend the original commits with the fixes and force-push the branch that is the source of the PR
  • using the 'merge' button for PRs should be the exception

It is also important to maintain the original author of the pull request, giving them credit for their contribution. This is also useful when compiling various contribution metrics, e.g. in Kibble.

Accepting new significant contributions

When accepting an external contribution we will import it into the sling-whiteboard repository. Before making a new release, we will move it to its own repository with the release manager also proposing a proper artifact id and therefore repository name.

It is recommended to provide ownership information when accepting new contributions by maintaining the original Author git header.

See also dev@sling - Where do we put new git modules?

Code donations

In case of code developed externally and not initially intended to be hosted at the ASF IP clearance is required. The general rules are outlined at . For a hands-on example, the Sling Journal-based Content Distribution is a good example:

Creating new repositories

Git repository creation

Repository creation is open only to PMC members. If you are not part of the PMC please ask on and someone will do this for you.

When creating new repositories we follow the convention of deriving the repository name from the Maven artifactId. The full logic can be found in the script, but the gist is:

  1. Append sling- to the artifact id if not there ( required by ASF infra conventions )
  2. Replace all dots with dashes ( ASF infra does not allow dots in repository names )

It is recommended to announce the intention on the mailing list, without calling a formal vote, since renaming repositories requires ASF infra manual intervention.

Creating a new repository is done using the web UI at . Please fill in the fields in the following manner:

  • Name: artifact Id , dots replaced with slashes. Should not contain the sling-  prefix as the form will auto-insert it in the 'Generated Name' field
  • Repository Description: name  from the pom.xml, otherwise short summary of the form Apache Sling Foo
  • Commit Notification List:
  • GitHub Notification List:

See a recent example below

Default branch name

Sling uses the default branch name master . To keep things simple for our tooling ( repo tool, Jenkins ) please create the repository locally and use master  as a branch name when pushing the initial changes to the repository. See Removal of problematic language for more context.

$ mkdir sling-new-repo
$ cd sling-new-repo
$ git init -b master

See also the discussion from INFRA-22359 - Getting issue details... STATUS

Permission propagation

The scripts will be created in gitbox and github at the same time, but permissions will be granted to the GitHub repository sometime later, due to the way ASF infra tooling works. If permissions don't appear in two hours, raise an INFRA ticket. In the meantime you can use the gitbox backend to push your changes.

Importing existing code from the whiteboard

If you have code that exists in the whiteboard and you want to move it to a separate repository it is recommended to keep the history. The steps to achieve that are below, given that ${FOLDER} is the folder from the Sling Whiteboard that you want to move to a new repository, and that ${NEW_REPO}  is the name of the new repository. The new repository should already be created.

1. Clone the whiteboard repository

$ git clone
$ cd sling-whiteboard

2. Reduce the repository to only the subfolder you're interested in

$ git filter-branch --prune-empty --subdirectory-filter ${FOLDER}

3. Change the origin remote URL to the desired one

$ git remote set-url origin${NEW_REPO}.git

4. Review your changes and push them

$ ls -1
$ git log
$ git push -u origin master


Maven SCM settings

The SCM settings from the pom.xml file are read by various tools, but most often used by the maven-scm-plugin  when releasing. We set the connection and developerScm settings to reference the ASF-maintained gitbox service, but use GitHub for the URL since it offers a better browsing experience and receives special treatment from some tools, such as renovate.

pom.xml scm settings example

Update the repo manifest

Regenerate the default.xml manifest form the sling-aggregator repo using  groovy collect-sling-repos.groovy > default.xml .

Update local Sling repo checkout

Execute the following comman in the root of the Sling repo checkout

$ repo sync -j 16
$ cd ${NEW_REPO}
$ git checkout master

Boilerplate files

Most of the files can be copied from any repository. We'll use org-apache-sling-api  as an example.

$ cd org-apache-sling-api
$ cp Jenkinsfile LICENSE .gitignore ../${NEW_REPO}

Generate a default .asf.yaml  file and update it, if applicable:

$ cd aggregator
$ groovy ./scripts/update-asf-yaml.groovy ../org-apache-sling-commons-metrics-prometheus/

See Git - .asf.yaml features for more details:

  • tags: include initially sling  and java  (or other programming language, as applicable )
  • homepage: module documentation on Sling website, or the Sling homepage if none exists
  • description: the name from the pom.xml 


The sling-aggregator/ script automates the creation of badges for the README. You will need a valid GitHub token for it. To add the badges for just a single repository, run.

$ cd aggregator
$ groovy ./generate-project-badges.groovy ../ ${NEW_REPO}

Enroll in Kibble

See Repository analysis with Kibble .

Onboard to SonarCloud

See the onboarding section in SonarCloud analysis .

Customize GitHub settings

By placing an .asf.yaml file one can customize certain GitHub settings like label, features and merge options.

Creating links to Git commits

To quickly create links to Git commits in JIRA a script such as the one below can be used:
#!/bin/sh -e
if [ $# -eq 0 ]; then
hash=$(git rev-parse --short ${commit})
base=$(git remote get-url origin)
echo "[commit ${hash}|${url}]"
  • No labels