SNCosmo follows the same general development workflow as astropy and many other open-source software projects. The astropy development workflow page documents the process in some detail. While you should indeed read that page, it can seem a bit overwhelming at first. So, we present here a rough outline of the process, and try to explain the reasoning behind it.
The process is centered around git and GitHub, so you need to know how to use basic git commands and also have a GitHub account. There is a “blessed” copy of the repository at https://github.com/sncosmo/sncosmo. Individual contributors make changes to their own copy (or “fork” or “clone” in git parlance) of the repository, e.g., https://github.com/kbarbary/sncosmo, then ask that their changes be merged into the “blessed” copy via a Pull Request (PR) on GitHub. A maintainer (currently Kyle) will review the changes in the PR, possibly ask for alterations, and then eventually merge the change.
This seems overly complex at first glance, but there are two main benefits to this process: (1) Anyone is free to try out any crazy change they want and share it with the world on their own GitHub account, without affecting the “blessed” repository, and (2) Any proposed changes are reviewed and discussed by at least one person (the maintainer) before being merged in.
Hit the “fork” button in the upper right hand corner of the https://github.com/sncosmo/sncosmo page. This creates a clone of the repository on your personal github account.
Get it onto your computer (replace username with your GitHub username):
git clone email@example.com:username/sncosmo.git
Add the “blessed” version as a remote:
git remote add upstream firstname.lastname@example.org:sncosmo/sncosmo.git
This will allow you to update your version to reflect new changes to the blessed repository that others have made).
Check that everything is OK:
$ git remote -v origin email@example.com:username/sncosmo.git (fetch) origin firstname.lastname@example.org:username/sncosmo.git (push) upstream email@example.com:sncosmo/sncosmo.git (fetch) upstream firstname.lastname@example.org:sncosmo/sncosmo.git (push)
You can call the remotes anything you want. “origin” and “upstream” have no intrinsic meaning for git; they’re just nicknames. The astropy documentation calls them “your-github-username” and “astropy” respectively.
Every time you want to make a contribution:¶
Ensure that the clone of the repository on your local machine is up-to-date with the latest upstream changes by doing
git fetch upstream. This updates your local “remote tracking branch”, called
Create a “topic branch” for the change you want to make. If you plan to make enhancements to the simulation code, name the branch something like “simulation-enhancements”:
git branch simulation-enhancements upstream/master
upstream/masteris where the branch branches off from.)
Move to the branch you just created:
git checkout simulation-enhancements
Make changes, ensure that they work, etc. Make commits as you go.
Once you’re happy with the state of your branch, push it to your GitHub account for the world to see:
git push origin simulation-enhancements
Create a PR: Go to your copy on github (https://github.com/username/sncosmo) select the branch you just pushed in the upper left-ish of the page, and hit the green button next to it. (It has a mouse-over “compare, review, create a pull request”)
What happens when the upstream branch is updated?¶
Suppose that you are following the above workflow: you created a topic
simulation-enhancements and made a few commits on that
branch. You now want to create a pull request, but there’s a problem:
while you were working, more commmits were added to the
upstream/master branch on GitHub. The history of your branch has
now diverged from the main development branch! What to do?
Fetch the changes made to the upstream branch on so that you can deal with the changes locally:
git fetch upstream
This will update your local branch
upstream/master(and any other
upstreambranches) to the match the state of the upstream branch on GitHub. It doesn’t do any merging or resolving, it just makes the new changes to
There are two options for this next step:
rebasewith the latter being preferred for this purpose. Assuming you are on your branch
simulation-enhancements, you could do
git merge upstream/master. This would create a merge commit that merges the diverged histories back together. This works, but it can end up creating a confusing commit history, particularly if you repeat this process several times while working on your new branch. Instead, you can do:
git rebase upstream/master
This actually rewrites your commits to make it look like they started from where
upstream/masternow is, rather than where it was when you started work on your
simulation-enhancementsbranch. Your branch will have the exact same contents as if you had used
git merge, but the history will be different than it would have been if you had merged. In particular, there is no merge commit created, because the history has been rewritten so that your branch starts where
upstream/masterends, and there is no divergent history to resolve. This means you can rebase again and again without creating a convoluted history full of merges back and forth between the branches.
Trying out new ideas¶
git branches are the best way to try out new ideas for code
modifications or additions. You don’t even have to tell anyone about
your bad ideas, since branches are local! They only become world
visible when you push them to GitHub. If, after making several
commits, you decide that your new branch
sucks, you can just create a new branch starting from upstream/master
again. If it is a really terrible idea you never want to see again,
you can delete it by doing
git branch -D simulation-enhancements.
Obviously this isn’t a complete guide to git, but hopefully it jump-starts the git learning process.
Developer’s documentation: release procedure¶
These are notes mainly for the one person that manages releases. Yes, this could be more automated, but it isn’t done very often, and involves some human verification.
docs/history.rstwith a summary of the new version’s changes.
- Bump version in
- Check copyright year in
- Build package and docs and check that docs look good.
git clean -dfx
- Check that the tarball in
dist/can be unpacked and that
setup.py testsucceeds. Bonus: create a fresh conda environment (or virtual environment) with minimal requirements and install and test in that.
setup.py sdist upload
- If not a bugfix release, create a feature branch. For example,
git branch v1.1.x.
- Tag the release. For example,
git tag v1.1.0.
- On master, bump version in
setup.pyto the next development version and add the next development version to
- Push repo changes to GitHub. For example:
git push upstream master v1.1.x v1.1.0.
Docs and conda
- On readthedocs.org, set the new feature branch to “active”.
- To trigger new conda build, edit version number in requirements.txt in https://github.com/astropy/conda-builder-affiliated and submit a pull request.
- Once conda build succeeds, make the new feature branch the default on readthedocs.org.