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(docs) Add COMMITTERS.md to guide committers

Without this patch the information a committer needs to possess in order
to merge contributions is spread all over the place.  The information is
also out of date.

This patch addresses the problem by consolidating the information into a
single place in the root of the project repository itself.
COMMITTERS.md should replace the following documents:

 * http://projects.puppetlabs.com/projects/puppet/wiki/Engineering_Process_Minimal_HOWTO
 * http://projects.puppetlabs.com/projects/puppet/wiki/Puppet_Design_Guidelines
 * http://projects.puppetlabs.com/projects/puppet/wiki/Internal_Development_Process
 * http://projects.puppetlabs.com/projects/puppet/wiki/Engineering_done_done

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1 parent 15fd642 commit ce73c7123b7a40f6182941c8b328d5b16bdce6de @jeffmccune jeffmccune committed Jan 17, 2013
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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](http://goo.gl/XRH2J).
+
+Therefore, it is the responsibility of the committer to re-base the change set
+on the appropriate branch which should receive the contribution.
+
+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. All other base branches will
+be associated with a specific released version of Puppet, e.g. 2.7.x and 3.0.x.
+
+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. Older minor releases in a major release do not get patched. Before
+the switch to [semantic versions](http://semver.org/) 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.
+
+How to commit a change set to multiple base branches
+---
+
+A change set may apply to multiple releases. In this situation the change set
+needs to be committed to multiple base branches. This section provides a guide
+for how to merge patches across releases, e.g. 2.7 is patched, how should the
+changes be applied to 3.0?
+
+First, merge the change set into the lowest numbered base branch, e.g. 2.7.
+Next, merge the changed base branch up through all later base branches by using
+the `--no-ff --log` git merge options. We commonly refer to this as our "merge
+up process" because we merge in once, then merge up multiple times.
+
+When a new minor release branch is created (e.g. 3.1.x) then the previous one
+is deleted (e.g. 3.0.x). Any security or urgent fixes that might have to be
+applied to the older code line is done by creating an ad-hoc branch from the
+tag of the last patch release of the old minor line.
+
+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](https://jenkins.puppetlabs.com/view/Puppet%20FOSS/)
+ 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.
+
+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 3.1.x
+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 3.1.x. The committer creates a new branch then re-bases the
+change set:
+
+ $ git branch bug/3.1.x/fix_foo_error
+ $ git rebase --onto 3.1.x master bug/3.1.x/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/3.1.x/fix_foo_error`, then take the changes that were previously
+based on `master` and re-base them onto `3.1.x`.
+
+Now that we have a topic branch containing the change set based on the correct
+release branch, the committer merges in:
+
+ $ git checkout 3.1.x
+ Switched to branch '3.1.x'
+ $ git merge --no-ff --log bug/3.1.x/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 up:
+
+ $ git checkout master
+ Switched to branch 'master'
+ $ git merge --no-ff --log 3.1.x
+ 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 "in and up." the committer pushes. (Note,
+the checklist should be complete at this point.) Note that both the 3.1.x and
+master branches are being pushed at the same time.
+
+ $ git push puppetlabs master:master 3.1.x:3.1.x
+
+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.

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