# 12.2. GitHub, Git, and related topics

## 12.2.1. GitHub

PMIx’s Git repository is hosted at GitHub.

1. First, you will need a Git client. We recommend getting the latest version available. If you do not have the command `git` in your path, you will likely need to download and install Git.

2. openpmix is the main PMIx repository where most active development is done. Git clone this repository. Note that the use of the `--recursive` CLI option is necessary because PMIx uses Git submodules:

       shell$ git clone --recursive https://github.com/openpmix/openpmix.git

Note that Git is natively capable of using many forms of web proxies. If your network setup requires the user of a web proxy, consult the Git documentation for more details.

## 12.2.2. Git commits: open source / contributor’s declaration

In order to remain open source, all new commits to the PMIx repository must include a `Signed-off-by:` line, indicating the submitter’s agreement to the PMIx Contributor’s Declaration.

Tip

You can use the `-s` option to `git commit` to automatically add the `Signed-off-by:` line to your commit message.

## 12.2.3. Git branch scheme

Generally, PMIx has two types of branches in its Git repository:

1. `master`:

   - All active development occurs on the `master` branch (new features, bug fixes, etc.).

2. Release branches of the form `vMAJOR.MINOR.x` (e.g., `v4.0.x`, `v4.1.x`, `v5.0.x`).

   - The `.x` suffix indicates that this branch is used to create all releases in the PMIx vMAJOR.MINOR series.

   - Periodically, the PMIx community will make a new release branch, typically from `master`.

   - A Git tag of the form `vMAJOR.MINOR.RELEASE` is used to indicate the specific commit on a release branch from where official PMIx release tarball was created (e.g., `v4.1.0`, `v4.1.1`, `v4.1.2`, etc.).

Once a bug is fixed or a new feature is implemented on `master`, it is cherry-picked over to the relevant release branch(es).

Attention

It may seem odd to some, but the PMIx community development model does not PR bug fixes or new features directly to release branches. Instead, initial bug-fix / feature PRs are generally first made to `master`.

This helps us ensure that future releases (with `master` as a Git ancestor) will contain the bug fix / feature.

For example:

    shell$ git checkout master
    shell$ git pull --rebase
    shell$ git checkout pr/bug-fix

    # ... make changes / fix a bug / etc. ...

    shell$ git add ...
    shell$ git commit -s ...
    shell$ git push myfork

At this point, you go create a PR from your fork’s `pr/bug-fix` branch to the PMIx community GitHub repo `master` branch. Work with the community to get the PR completed and merged. Then you can open a new PR to cherry pick the Git commits from that bug fix to each of the relevant release branches.

Depending on how far the release branch has diverged from `master`, there may be some porting effort involved in the cherry-pick.

For example, if your bug fix on `master` is comprised of a single Git commit hash `123abc`:

    # Fetch all upstream git activity, including the merge of the "master" PR.
    shell$ get fetch --all

    # Check out the target release branch, and advance to the most recent commit.
    shell$ git checkout v5.0.x
    shell$ git pull --rebase

    # Make a branch for your bug fix
    shell$ git checkout -b pr/v5.0.x/bug-fix
    # Cherry pick the commit from the "master" branch
    shell$ git cherry-pick -x 123abc
    # Push to your fork
    shell$ git push myfork

The PMIx development community requires adding the following line to the commit message of cherry-picked commits on release branches:

    (cherry picked from commit [git_hash_of_original_commit])

Note

Note the use of the `-x` option to `git cherry-pick`. This option automatically adds the `(cherry picked from ...)` line to your commit message.

Rationale

Git does not actually store any meta data about Git cherry-picks in the commit. Having a standardized text line containing the source Git commit hash in the commit messages helps the PMIx development community track where commits came from on release branches, and therefore allows us to check whether all relevant commits have been ported to a given release branch.

Once your commits are ready and pushed up to your fork, make a PR to the target release branch.

Warning

A GitHub PR CI job checks all commits on release branches for the `(cherry picked from...)` line. It will also ensure that the Git hash cited in that line actually exists on the `master` branch.

This check ensures that commits are not made to release branches before their corresponding `master` PR was merged.

All this being said, sometimes there is a need for a non-cherry-picked commit on a release branch. E.g., sometimes a release branch has diverged so much that the bug no longer exists on `master`. It would therefore not make sense — or even be impossible — to commit the bug fix in question to `master`.

In such cases, make a regular PR to the target branch (with commits that do not include `(cherry picked from ...)` lines). In the PR description, add a line with the following token:

    bot:notacherrypick

This tells the GitHub CI job that this PR contains commits that are not cherry-picked from `master`.

Warning

`bot:notacherrypick` should only be used when absolutely necessary. It is not a license to avoid the process of PR’ing to `master` first.

## 12.2.4. CI (testing)

The PMIx community generally runs a bunch of tests on each PR (Continuous Integration / CI). These tests are a mixture of GitHub Actions and other CI systems (e.g., Jenkins). Examples include (but are not limited to):

> - Check each Git commit for bozo email addresses

> - Check that each Git commit contains a `Signed-off-by` line

> - Check that commits on release branches contain a cherry-pick notice

> - Build and publish the docs

> - Build PMIx in a variety of environments and run sanity tests with that installation