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Committing changes to Puppet

We would like to make it easier for community members to contribute to Puppet using pull requests, even if it makes the task of reviewing and committing these changes a little harder. Pull requests are only ever based on a single branch, however, we maintain more than one active branch. As a result contributors should target their changes at the master branch. This makes the process of contributing a little easier for the contributor since they don't need to concern themselves with the question, "What branch do I base my changes on?" This is already called out in the CONTRIBUTING.md.

Therefore, it is the responsibility of the committer to re-base the change set on the appropriate branch which should receive the contribution.

It is also the responsibility of the committer to review the change set in an effort to make sure the end users must opt-in to new behavior that is incompatible with previous behavior. We employ the use of feature flags as the primary way to achieve this user opt-in behavior. Finally, it is the responsibility of the committer to make sure the master and stable branches are both clean and working at all times. Clean means that dead code is not allowed, everything needs to be usable in some manner at all points in time. Stable is not an indication of the build status, but rather an expression of our intent that the stable branch does not receive new functionality.

The rest of this document addresses the concerns of the committer. This document will help guide the committer decide which branch to base, or re-base a contribution on top of. This document also describes our branch management strategy, which is closely related to the decision of what branch to commit changes into.

Terminology

Many of these terms have more than one meaning. For the purposes of this document, the following terms refer to specific things.

contributor - A person who makes a change to Puppet and submits a change set in the form of a pull request.

change set - A set of discrete patches which combined together form a contribution. A change set takes the form of Git commits and is submitted to Puppet in the form of a pull request.

committer - A person responsible for reviewing a pull request and then making the decision what base branch to merge the change set into.

base branch - A branch in Git that contains an active history of changes and will eventually be released using semantic version guidelines. The branch named master will always exist as a base branch. The other base branches are stable, and security described below.

master branch - The branch where new functionality that are not bug fixes is merged.

stable branch - The branch where bug fixes against the latest release or release candidate are merged.

security - Where critical security fixes are merged. These change sets will then be merged into release branches independently from one another. (i.e. no merging up). Please do not submit pull requests against the security branch and instead report all security related issues to security@puppetlabs.com as per our security policy published at https://puppetlabs.com/security/.

Committer Guide

This section provides a guide to follow while committing change sets to Puppet base branches.

How to decide what release(s) should be patched

This section provides a guide to help a committer decide the specific base branch that a change set should be merged into.

The latest minor release of a major release is the only base branch that should be patched. These patches will be merged into master if they contain new functionality. They will be merged into stable and master if they fix a critical bug. Older minor releases in a major release do not get patched.

Before the switch to semantic versions committers did not have to think about the difference between minor and major releases. Committing to the latest minor release of a major release is a policy intended to limit the number of active base branches that must be managed.

Security patches are handled as a special case. Security patches may be applied to earlier minor releases of a major release, but the patches should first be merged into the security branch. Security patches should be merged by Puppet Labs staff members. Pull requests should not be submitted with the security branch as the base branch. Please send all security related information or patches to security@puppetlabs.com as per our Security Policy.

The CI systems are configured to run against master and stable. Over time, these branches will refer to different versions, but their name will remain fixed to avoid having to update CI jobs and tasks as new versions are released.

How to commit a change set to multiple base branches

A change set may apply to multiple branches, for example a bug fix should be applied to the stable release and the development branch. In this situation the change set needs to be committed to multiple base branches. This section provides a guide for how to merge patches into these branches, e.g. stable is patched, how should the changes be applied to master?

First, rebase the change set onto the stable branch. Next, merge the change set into the stable branch using a merge commit. Once merged into stable, merge the same change set into master without doing a rebase as to preserve the commit identifiers. This merge strategy follows the git flow model. Both of these change set merges should have a merge commit which makes it much easier to track a set of commits as a logical change set through the history of a branch. Merge commits should be created using the --no-ff --log git merge options.

Any merge conflicts should be resolved using the merge commit in order to preserve the commit identifiers for each individual change. This ensures git branch --contains will accurately report all of the base branches which contain a specific patch.

Using this strategy, the stable branch need not be reset. Both master and stable have infinite lifetimes. Patch versions, also known as bug fix releases, will be tagged and released directly from the stable branch. Major and minor versions, also known as feature releases, will be tagged and released directly from the master branch. Upon release of a new major or minor version all of the changes in the master branch will be merged into the stable branch.

Code review checklist

This section aims to provide a checklist of things to look for when reviewing a pull request and determining if the change set should be merged into a base branch:

  • All tests pass
  • Are there any platform gotchas? (Does a change make an assumption about platform specific behavior that is incompatible with other platforms? e.g. Windows paths vs. POSIX paths.)
  • Is the change backwards compatible? (It should be)
  • Are there YARD docs for API changes?
  • Does the change set also require documentation changes? If so is the documentation being kept up to date?
  • Does the change set include clean code? (software code that is formatted correctly and in an organized manner so that another coder can easily read or modify it.) HINT: git diff master --check
  • Does the change set conform to the contributing guide?

Commit citizen guidelines:

This section aims to provide guidelines for being a good commit citizen by paying attention to our automated build tools.

  • Don’t push on a broken build. (A broken build is defined as a failing job in the Puppet FOSS page.)
  • Watch the build until your changes have gone through green
  • Update the ticket status and target version. The target version field in our issue tracker should be updated to be the next release of Puppet. For example, if the most recent release of Puppet is 3.1.1 and you merge a backwards compatible change set into master, then the target version should be 3.2.0 in the issue tracker.)
  • Ensure the pull request is closed (Hint: amend your merge commit to contain the string closes #123 where 123 is the pull request number and github will automatically close the pull request when the branch is pushed.)

Example Procedure

This section helps a committer rebase a contribution onto an earlier base branch, then merge into the base branch and up through all active base branches.

Suppose a contributor submits a pull request based on master. The change set fixes a bug reported against Puppet 3.1.1 which is the most recently released version of Puppet.

In this example the committer should rebase the change set onto the stable branch since this is a bug rather than new functionality.

First, the committer pulls down the branch using the hub gem. This tool automates the process of adding the remote repository and creating a local branch to track the remote branch.

$ hub checkout https://github.com/puppetlabs/puppet/pull/1234
Branch jeffmccune-fix_foo_error set up to track remote branch fix_foo_error from jeffmccune.
Switched to a new branch 'jeffmccune-fix_foo_error'

At this point the topic branch is a descendant of master, but we want it to descend from stable. The committer rebases the change set onto stable.

$ git branch bug/stable/fix_foo_error
$ git rebase --onto stable master bug/stable/fix_foo_error
First, rewinding head to replay your work on top of it...
Applying: (#23456) Fix FooError that always bites users in 3.1.1

The git rebase command may be interpreted as, "First, check out the branch named bug/stable/fix_foo_error, then take the changes that were previously based on master and re-base them onto stable.

Now that we have a topic branch containing the change set based on the stable release branch, the committer merges in:

$ git checkout stable
Switched to branch 'stable'
$ git merge --no-ff --log bug/stable/fix_foo_error
Merge made by the 'recursive' strategy.
 foo | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo

Once merged into the first base branch, the committer merges the stable branch into master, being careful to preserve the same commit identifiers.

$ git checkout master
Switched to branch 'master'
$ git merge --no-ff --log stable
Merge made by the 'recursive' strategy.
 foo | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo

Once the change set has been merged into one base branch, the change set should not be modified in order to keep the history clean, avoid "double" commits, and preserve the usefulness of git branch --contains. If there are any merge conflicts, they are to be resolved in the merge commit itself and not by re-writing (rebasing) the patches for one base branch, but not another.

Once the change set has been merged into stable and into master, the committer pushes. Please note, the checklist should be complete at this point. It's helpful to make sure your local branches are up to date to avoid one of the branches failing to fast forward while the other succeeds. Both the stable and master branches are being pushed at the same time.

$ git push puppetlabs master:master stable:stable

That's it! The committer then updates the pull request, updates the issue in our issue tracker, and keeps an eye on the build status.