.. _development-workflow:

=======================
Workflow for Developers
=======================

In the present document, we refer to the Astropy ``master`` branch, as the
*trunk*.

.. _forking:

Creating a fork
===============

You need to do this only once for each package you want to contribute to. The
instructions here are very similar to the instructions at
http://help.github.com/fork-a-repo/ |emdash| please see that page for more
details. We're repeating some of it here just to give the specifics for the
Astropy_ project, and to suggest some default names.

Set up and configure a GitHub account
-------------------------------------

If you don't have a GitHub account, go to the GitHub page, and make one.

You then need to configure your account to allow write access |emdash| see
the *Generating SSH keys* help on `GitHub Help`_.

Create your own fork of a repository
------------------------------------

The following example shows how to fork the core ``astropy`` repository, but the same applies to other packages:

#. Log into your GitHub account.

#. Go to the `Astropy GitHub`_ home.

#. Click on the *fork* button:

   .. image:: forking_button.png

   Now, after a short pause and some 'Hardcore forking action', you
   should find yourself at the home page for your own forked copy of Astropy_.

Setting up the fork to work on
------------------------------

.. _linking-to-upstream:

Overview
^^^^^^^^

This is done using::

    git clone git@github.com:your-user-name/astropy.git
    cd astropy
    git remote add upstream git://github.com/astropy/astropy.git

In detail
^^^^^^^^^

#. Clone your fork to the local computer::

    git clone git@github.com:your-user-name/astropy.git

#. Change directory to your new repo::

    cd astropy

   Then type::

    git branch -a

   to show you all branches.  You'll get something like::

    * master
    remotes/origin/master

   This tells you that you are currently on the ``master`` branch, and
   that you also have a ``remote`` connection to ``origin/master``.
   What remote repository is ``remote/origin``? Try ``git remote -v`` to
   see the URLs for the remote.  They will point to your GitHub fork.

   Now you want to connect to the Astropy repository, so you can
   merge in changes from the trunk::

    cd astropy
    git remote add upstream git://github.com/astropy/astropy.git

   ``upstream`` here is just the arbitrary name we're using to refer to the
   main Astropy_ repository.

   Note that we've used ``git://`` for the URL rather than ``git@``. The
   ``git://`` URL is read only. This means we that we can't accidentally (or
   deliberately) write to the upstream repo, and we are only going to use it
   to merge into our own code.

   Just for your own satisfaction, show yourself that you now have a new
   'remote', with ``git remote -v show``, giving you something like::

    upstream   git://github.com/astropy/astropy.git (fetch)
    upstream   git://github.com/astropy/astropy.git (push)
    origin     git@github.com:your-user-name/astropy.git (fetch)
    origin     git@github.com:your-user-name/astropy.git (push)

   Your fork is now set up correctly, and you are ready to hack away.

.. _develop-mode:

Installing Astropy in develop mode
==================================

Astropy is designed so that the ``astropy`` package can generally be used
directly out of the source tree by using ``import astropy`` when running Python
in the source of an Astropy repository clone.  There are some caveats, however:

1. It is necessary to build C extensions in "inline" mode which copies the
   built shared libraries into the source tree::

       $ python setup.py build_ext --inline

2. If you change directories from the root of the repository clone the
   ``astropy`` package will no longer be importable, and other features may not
   work properly.

A more robust solution is to use the ``setup.py develop`` command.  This
semi-permanently installs Astropy on your path in such a way that ``astropy``
is always imported from your repository clone regardless of your working
directory.  This way any edits you make to the code in your repository will
always be immediately available next time you start a Python interpreter and
``import astropy``.

Develop mode can be easily disabled again by running
``setup.py develop -u``.

.. note::

    When switching branches it is not *generally* required to re-run
    ``setup.py develop``, though it may be necessary to run
    ``setup.py build_ext --inline`` again in case you think there might be
    differences in the C extensions between the two branches.

Another useful technique to avoid having to switch develop mode on and off
without disrupting production use of Astropy is to use virtualenv as explained
:ref:`below<using-virtualenv>`.

Workflow summary
================

This section gives a summary of the workflow once you have successfully forked
the repository, and details are given for each of these steps in the following
sections.

* Don't use your ``master`` branch for anything.  Consider deleting it.

* When you are starting a new set of changes, fetch any changes from the
  trunk, and start a new *feature branch* from that.

* Make a new branch for each separable set of changes |emdash| "one task, one
  branch" (`ipython git workflow`_).

* Name your branch for the purpose of the changes - e.g.
  ``bugfix-for-issue-14`` or ``refactor-database-code``.

* If you can possibly avoid it, avoid merging trunk or any other branches into
  your feature branch while you are working.

* If you do find yourself merging from the trunk, consider :ref:`rebase-on-trunk`

* Ask on the `astropy-dev mailing list`_ if you get stuck.

* Ask for code review!

This way of working helps to keep work well organized, with readable history.
This in turn makes it easier for project maintainers (that might be you) to
see what you've done, and why you did it.

See `linux git workflow`_ and `ipython git workflow`_ for some explanation.

Deleting your master branch
===========================

It may sound strange, but deleting your own ``master`` branch can help reduce
confusion about which branch you are on.  See `deleting master on github`_ for
details.

.. _update-mirror-trunk:

Updating the mirror of trunk
============================

From time to time you should fetch the upstream (trunk) changes from GitHub::

   git fetch upstream

This will pull down any commits you don't have, and set the remote branches to
point to the right commit. For example, 'trunk' is the branch referred to by
(remote/branchname) ``upstream/master`` - and if there have been commits since
you last checked, ``upstream/master`` will change after you do the fetch.

.. _make-feature-branch:

Making a new feature branch
===========================

When you are ready to make some changes to the code, you should start a new
branch. Branches that are for a collection of related edits are often called
'feature branches'.

Making an new branch for each set of related changes will make it easier for
someone reviewing your branch to see what you are doing.

Choose an informative name for the branch to remind yourself and the rest of
us what the changes in the branch are for. For example ``add-ability-to-fly``,
or ``buxfix-for-issue-42``.

::

    # Update the mirror of trunk
    git fetch upstream

    # Make new feature branch starting at current trunk
    git branch my-new-feature upstream/master
    git checkout my-new-feature

Generally, you will want to keep your feature branches on your public GitHub_
fork. To do this, you `git push`_ this new branch up to your
github repo. Generally (if you followed the instructions in these pages, and
by default), git will have a link to your GitHub repo, called ``origin``. You
push up to your own repo on GitHub with::

   git push origin my-new-feature

In git >= 1.7 you can ensure that the link is correctly set by using the
``--set-upstream`` option::

   git push --set-upstream origin my-new-feature

From now on git will know that ``my-new-feature`` is related to the
``my-new-feature`` branch in the GitHub repo.

.. _edit-flow:

The editing workflow
====================

Overview
--------

::

   git add my_new_file
   git commit -am 'NF - some message'
   git push

In more detail
--------------

#. Make some changes

#. See which files have changed with ``git status`` (see `git status`_).
   You'll see a listing like this one::

     # On branch ny-new-feature
     # Changed but not updated:
     #   (use "git add <file>..." to update what will be committed)
     #   (use "git checkout -- <file>..." to discard changes in working directory)
     #
     #    modified:   README
     #
     # Untracked files:
     #   (use "git add <file>..." to include in what will be committed)
     #
     #    INSTALL
     no changes added to commit (use "git add" and/or "git commit -a")

#. Check what the actual changes are with ``git diff`` (`git diff`_).

#. Add any new files to version control ``git add new_file_name`` (see
   `git add`_).

#. Add any modified files that you want to commit using
   ``git add modified_file_name``  (see `git add`_).

#. Once you are ready to commit, check with ``git status`` which files are about to be committed::

    # Changes to be committed:
    #   (use "git reset HEAD <file>..." to unstage)
    #
    #    modified:   README

   Then use ``git commit -m 'A commit message'``. The ``m`` flag just
   signals that you're going to type a message on the command line. The `git
   commit`_ manual page might also be useful.

#. To push the changes up to your forked repo on GitHub, do a ``git
   push`` (see `git push`_).

Asking for your changes to be reviewed or merged
================================================

When you are ready to ask for someone to review your code and consider a merge:

#. Go to the URL of your forked repo, say
   ``http://github.com/your-user-name/astropy``.

#. Use the 'Switch Branches' dropdown menu near the top left of the page to
   select the branch with your changes:

   .. image:: branch_dropdown.png

#. Click on the 'Pull request' button:

   .. image:: pull_button.png

   Enter a title for the set of changes, and some explanation of what you've
   done. Say if there is anything you'd like particular attention for - like a
   complicated change or some code you are not happy with.

   If you don't think your request is ready to be merged, just say so in your
   pull request message.  This is still a good way of getting some preliminary
   code review.

.. _using-virtualenv:

Using virtualenv
================

`virtualenv`_ is a tool for creating and activating isolated Python
environments that allow installing and experimenting with Python packages
without disrupting your production Python environment.  When using commands
such as ``setup.py develop``, for example, it is strong recommended to do
so within a virtualenv.  This is generally preferable to installing a
development version of Astropy into your system site-packages and having to
keep track of whether or not your environment is in a "known good"
configuration for production/science use.

Using a virtualenv is also a good way to try out new versions of software that
you're not actively doing development work on without disrupting your normal
production environment.

We won't provide a full tutorial on using virtualenv here--the virtualenv
documentation linked to above is a better place to start.  But here is a quick
overview on how to set up a virtualenv for Astropy development with your
default Python version:

1. Install virtualenv::

       $ pip install virtualenv

   or::

       $ easy_install virtualenv

   or (on Debian/Ubuntu)::

       $ sudo apt-get install python-virtualenv

   etc.

2. (Recommended) Create a root directory for all your virtualenvs under a path
   you have write access to.  For example::

       $ mkdir ~/.virtualenvs

3. Create the Astropy virtualenv::

       $ virtualenv --distribute --system-site-packages ~/.virtualenvs/astropy-dev

   The ``--system-site-packages`` option inherits all packages already
   installed in your system site-packages directory; this frees you from having
   to reinstall packages like Numpy and Scipy in the virtualenv.  However, if
   you would like your virtualenv to use a development version of Numpy, for
   example, you can still install Numpy into the virtualenv and it will take
   precedence over the version installed in site-packages.

4. Activate the virtualenv::

       $ source ~/.virtualenvs/astropy-dev/bin/activate

   or if you're using a csh-variant::

       $ source ~/.virtualenvs/astropy-dev/bin/activate.csh

   virtualenv works on Windows too--see the documentation for details.

5. If the virtualenv successfully activated its name should appear in your
   shell prompt::

       (astropy-dev) $

   The virtualenv can be disabled at any time by entering::

       (astropy-dev) $ deactivate

6. Now as long as the virtualenv is activated packages you install with
   ``pip``, ``easy_install``, or by manually running ``python setup.py
   install`` will automatically install into your virtualenv instead of the
   system site-packages.  Consider installing Astropy in develop mode into the
   virtualenv as described :ref:`above<develop-mode>`.

Using virtualenv with IPython
-----------------------------

.. note::

    As of IPython 0.13 this functionality is built into IPython and these steps
    are not necessary for IPython to recognize that it's running with a
    virtualenv enabled.

Each virtualenv has its own ``bin/``, and as IPython is written in pure Python
one can always install IPython directly into a virtualenv.  However, if you
would rather not have to install IPython every time you create a virtualenv, it
also suffices to make IPython virtualenv-aware.

1. Check to see if you already have an IPython profile in
   ``~/.ipython/profile_default/``; if not, create one::

       $ ipython profile create

2. Edit ``~/.ipython/profile_default/ipython_config.py`` and add the
   following to the end::

       import os

       execfile(os.path.join(os.environ['HOME'], '.ipython', 'virtualenv.py'))

3. Finally, create the ``~/.ipython/virtualenv.py`` module::

    import site
    from os import environ
    from os.path import join
    from sys import version_info

    if 'VIRTUAL_ENV' in environ:
        virtual_env = join(environ.get('VIRTUAL_ENV'),
                           'lib',
                           'python%d.%d' % version_info[:2],
                           'site-packages')
        site.addsitedir(virtual_env)
        print 'VIRTUAL_ENV ->', virtual_env
        del virtual_env
    del site, environ, join, version_info

Now IPython will import all packages from your virtualenv where applicable.

.. note::

    This is not magic. If you switch to a virtualenv that uses a different
    Python version from your main IPython installation this won't help you--
    instead use the appropriate IPython installation for the Python version
    in question.

virtualenvwrapper
-----------------

`virtualenvwrapper`_ is a set of enhancements to virtualenv mostly implemented
through simple shell scripts and aliases.  It automatically organizes all your
virtualenvs under a single directory (as suggested above)--to create a new
virtualenv you can just use the `mkvirtualenv <env_name>` command and it will
automatically create a new virtualenv of that name in the default location.

To activate a virtualenv with virtualenvwrapper you don't need to think about
the environment's location of the filesystem or which activate script to run.
Simply run `workon <env_name>`.  You can also list all virtualenvs with
`lsvirtualenv`.  That just scratches the surface of the goodies included with
virtualenvwrapper.

The one caveat is that it does not support csh-like shells.  For csh-like
shells there exists `virtualenvwrapper-csh`_ which implements most of the
virtualenvwrapper functionality and is otherwise compatible with the original.
There also exists `virtualenvwrapper-win`_ which ports virtualenvwrapper to
Windows batch scripts.

venv
----

virtualenv is so commonly used in the Python development community that its
functionality was finally added to the standard library in Python 3.3 under
the name `venv`_.  venv has not gained wide use yet and is not explicitly
supported by tools like virtualenvwrapper, but it is expected to see wider
adoption in the future.

Some other things you might want to do
======================================

Delete a branch on GitHub
-------------------------

::

   # change to the master branch (if you still have one, otherwise change to
   # another branch)
   git checkout master

   # delete branch locally
   git branch -D my-unwanted-branch

   # delete branch on GitHub
   git push origin :my-unwanted-branch

(Note the colon ``:`` before ``test-branch``.  See also:
http://github.com/guides/remove-a-remote-branch

Several people sharing a single repository
------------------------------------------

If you want to work on some stuff with other people, where you are all
committing into the same repository, or even the same branch, then just
share it via GitHub.

First fork Astropy into your account, as from :ref:`forking`.

Then, go to your forked repository GitHub page, say
``http://github.com/your-user-name/astropy``

Click on the 'Admin' button, and add anyone else to the repo as a
collaborator:

   .. image:: pull_button.png

Now all those people can do::

    git clone git@githhub.com:your-user-name/astropy.git

Remember that links starting with ``git@`` use the ssh protocol and are
read-write; links starting with ``git://`` are read-only.

Your collaborators can then commit directly into that repo with the
usual::

     git commit -am 'ENH - much better code'
     git push origin master # pushes directly into your repo

Explore your repository
-----------------------

To see a graphical representation of the repository branches and
commits::

   gitk --all

To see a linear list of commits for this branch::

   git log

You can also look at the `network graph visualizer`_ for your GitHub
repo.

Finally the :ref:`fancy-log` ``lg`` alias will give you a reasonable
text-based graph of the repository.

.. _rebase-on-trunk:

Rebasing on trunk
-----------------

Let's say you thought of some work you'd like to do. You
:ref:`update-mirror-trunk` and :ref:`make-feature-branch` called
``cool-feature``. At this stage trunk is at some commit, let's call it E. Now
you make some new commits on your ``cool-feature`` branch, let's call them A,
B, C. Maybe your changes take a while, or you come back to them after a while.
In the meantime, trunk has progressed from commit E to commit (say) G::

          A---B---C cool-feature
         /
    D---E---F---G trunk

At this stage you consider merging trunk into your feature branch, and you
remember that this here page sternly advises you not to do that, because the
history will get messy. Most of the time you can just ask for a review, and
not worry that trunk has got a little ahead. But sometimes, the changes in
trunk might affect your changes, and you need to harmonize them. In this
situation you may prefer to do a rebase.

Rebase takes your changes (A, B, C) and replays them as if they had been made
to the current state of ``trunk``. In other words, in this case, it takes the
changes represented by A, B, C and replays them on top of G. After the rebase,
your history will look like this::

                  A'--B'--C' cool-feature
                 /
    D---E---F---G trunk

See `rebase without tears`_ for more detail.

To do a rebase on trunk::

    # Update the mirror of trunk
    git fetch upstream

    # Go to the feature branch
    git checkout cool-feature

    # Make a backup in case you mess up
    git branch tmp cool-feature

    # Rebase cool-feature onto trunk
    git rebase --onto upstream/master upstream/master cool-feature

In this situation, where you are already on branch ``cool-feature``, the last
command can be written more succinctly as::

    git rebase upstream/master

When all looks good you can delete your backup branch::

   git branch -D tmp

If it doesn't look good you may need to have a look at
:ref:`recovering-from-mess-up`.

If you have made changes to files that have also changed in trunk, this may
generate merge conflicts that you need to resolve - see the `git rebase`_ man
page for some instructions at the end of the "Description" section. There is
some related help on merging in the git user manual - see `resolving a
merge`_.

If your feature branch is already on GitHub and you rebase, you will have to force
push the branch; a normal push would give an error. If the branch you rebased is
called ``cool-feature`` and your GitHub fork is available as the remote called ``origin``,
you use this command to force-push::

   git push -f origin cool-feature

Note that this will overwrite the branch on GitHub, i.e. this is one of the few ways
you can actually lose commits with git.
Also note that it is never allowed to force push to the main astropy repo (typically
called ``upstream``), because this would re-write commit history and thus cause problems
for all others.

.. _recovering-from-mess-up:

Recovering from mess-ups
------------------------

Sometimes, you mess up merges or rebases. Luckily, in git it is relatively
straightforward to recover from such mistakes.

If you mess up during a rebase::

   git rebase --abort

If you notice you messed up after the rebase::

   # Reset branch back to the saved point
   git reset --hard tmp

If you forgot to make a backup branch::

   # Look at the reflog of the branch
   git reflog show cool-feature

   8630830 cool-feature@{0}: commit: BUG: io: close file handles immediately
   278dd2a cool-feature@{1}: rebase finished: refs/heads/my-feature-branch onto 11ee694744f2552d
   26aa21a cool-feature@{2}: commit: BUG: lib: make seek_gzip_factory not leak gzip obj
   ...

   # Reset the branch to where it was before the botched rebase
   git reset --hard cool-feature@{2}

.. _rewriting-commit-history:

Rewriting commit history
------------------------

.. note::

   Do this only for your own feature branches.

There's an embarrassing typo in a commit you made? Or perhaps the you
made several false starts you would like the posterity not to see.

This can be done via *interactive rebasing*.

Suppose that the commit history looks like this::

    git log --oneline
    eadc391 Fix some remaining bugs
    a815645 Modify it so that it works
    2dec1ac Fix a few bugs + disable
    13d7934 First implementation
    6ad92e5 * masked is now an instance of a new object, MaskedConstant
    29001ed Add pre-nep for a copule of structured_array_extensions.
    ...

and ``6ad92e5`` is the last commit in the ``cool-feature`` branch. Suppose we
want to make the following changes:

* Rewrite the commit message for ``13d7934`` to something more sensible.
* Combine the commits ``2dec1ac``, ``a815645``, ``eadc391`` into a single one.

We do as follows::

    # make a backup of the current state
    git branch tmp HEAD
    # interactive rebase
    git rebase -i 6ad92e5

This will open an editor with the following text in it::

    pick 13d7934 First implementation
    pick 2dec1ac Fix a few bugs + disable
    pick a815645 Modify it so that it works
    pick eadc391 Fix some remaining bugs

    # Rebase 6ad92e5..eadc391 onto 6ad92e5
    #
    # Commands:
    #  p, pick = use commit
    #  r, reword = use commit, but edit the commit message
    #  e, edit = use commit, but stop for amending
    #  s, squash = use commit, but meld into previous commit
    #  f, fixup = like "squash", but discard this commit's log message
    #
    # If you remove a line here THAT COMMIT WILL BE LOST.
    # However, if you remove everything, the rebase will be aborted.
    #

To achieve what we want, we will make the following changes to it::

    r 13d7934 First implementation
    pick 2dec1ac Fix a few bugs + disable
    f a815645 Modify it so that it works
    f eadc391 Fix some remaining bugs

This means that (i) we want to edit the commit message for ``13d7934``, and
(ii) collapse the last three commits into one. Now we save and quit the
editor.

Git will then immediately bring up an editor for editing the commit message.
After revising it, we get the output::

    [detached HEAD 721fc64] FOO: First implementation
     2 files changed, 199 insertions(+), 66 deletions(-)
    [detached HEAD 0f22701] Fix a few bugs + disable
     1 files changed, 79 insertions(+), 61 deletions(-)
    Successfully rebased and updated refs/heads/my-feature-branch.

and the history looks now like this::

     0f22701 Fix a few bugs + disable
     721fc64 ENH: Sophisticated feature
     6ad92e5 * masked is now an instance of a new object, MaskedConstant

If it went wrong, recovery is again possible as explained :ref:`above
<recovering-from-mess-up>`.

Converting a GitHub issue to a pull request
-------------------------------------------

Sometimes you have a branch in your own GitHub repository designed to
fix one particular issue.  If that issue is listed on GitHub, a natural
way to address it is to convert the issue to a pull request by
attaching code with the fix to the issue. This can currently only be
done using the GitHub API (there's no button or anything on the web
site that does it, at least as of 2/6/2012). There are two options to do this:

* You can use the script at https://gist.github.com/1750715 which will
  do this for you automatically - just download the script and run it as
  a python command-line script, using the ``python issue2pr.py --help``
  option to determine the precise usage.

* You can use the ``hub`` command-line utility provided `here
  <https://github.com/defunkt/hub>`_ by GitHub. Once installed, you can
  attach a branch to a pull request by doing::

          hub pull-request -i <ID> -b astropy:master -h <USER>:<BRANCH>

  where ``<ID>`` is the ID of the issue, ``<USER>`` is the username, and
  ``<BRANCH>`` is the name of the branch you want to attach to the
  issue. For example::

          hub pull-request -i 42 -b astropy:master -h galahad:feature

  will attach the ``feature`` branch from ``galahad``'s Astropy
  repository to issue 42.

  The ``hub`` command can do a lot more to interact with GitHub, so be
  sure to read their documentation. For example, you can fetch all
  branches of a repository for a given user by doing::

          hub fetch <USER>

.. include:: links.inc
