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docs/contributing/phabricator.rst

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				.. highlight:: bash

				.. _patch-submission:

				Submitting patches
				==================

				`Phabricator`_ is the tool that Software Heritage uses as its
				coding/collaboration forge.

				Software Heritage's Phabricator instance can be found at
				https://forge.softwareheritage.org/

				.. _Phabricator: http://phabricator.org/

				Code Review in Phabricator
				--------------------------

				We use the Differential application of Phabricator to perform
				:ref:`code reviews <code-review>` in the context of Software Heritage.

				* we use Git and ``history.immutable=true``
				(but beware as that is partly a Phabricator misnomer, read on)
				* when code reviews are required, developers will be allowed to push
				directly to master once an accepted Differential diff exists

				Configuration
				+++++++++++++

				Arcanist configuration
				^^^^^^^^^^^^^^^^^^^^^^

				Authentication
				~~~~~~~~~~~~~~

				First, you should install Arcanist and authenticate it to Phabricator::

				sudo apt-get install arcanist
				arc set-config default https://forge.softwareheritage.org/
				arc install-certificate

				arc will prompt you to login into Phabricator via web
				(which will ask your personal Phabricator credentials).
				You will then have to copy paste the API token from the web page to arc,
				and hit Enter to complete the certificate installation.

				Immutability
				~~~~~~~~~~~~

				When using git, Arcanist by default mess with the local history,
				rewriting commits at the time of first submission.
				To avoid that we use so called `history immutability`_

				.. _history immutability: https://secure.phabricator.com/book/phabricator/article/arcanist_new_project/#history-mutability-git

				To that end, you shall configure your ``arc`` accordingly::

				arc set-config history.immutable true

				Note that this does not mean that you are forbidden to rewrite
				your local branches (e.g., with ``git rebase``).
				Quite the contrary: you are encouraged to locally rewrite branches
				before pushing to ensure that commits are logically separated
				and your commit history easy to bisect.
				The above setting just means that arc will not rewrite commit
				history under your nose.

				Enabling ``git push`` to our forge
				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

				The way we've configured our review setup for continuous integration
				needs you to configure git to allow pushes to our forge.
				There's two ways you can do this : setting a ssh key to push over ssh,
				or setting a specific password for git pushes over https.

				SSH key for pushes
				~~~~~~~~~~~~~~~~~~

				In your forge User settings page (On the top right, click on your avatar,
				then click Settings), you have access to a Authentication >
				SSH Public Keys section (Direct link:
				``hxxps://forge.softwareheritage.org/settings/user/<your username>/page/ssh/``).
				You then have the option to upload a SSH public key,
				which will authenticate your pushes.

				You then need to configure ssh/git to use that key pair,
				for instance by editing the ``~/.ssh/config`` file.

				Finally, you should configure git to push over ssh when pushing to
				https://forge.softwareheritage.org, by running the following command::

				git config --global url.git@forge.softwareheritage.org:.pushInsteadOf https://forge.softwareheritage.org

				This lets git know that it should use ``git@forge.softwareheritage.org:``
				as a base url when pushing repositories cloned from
				forge.softwareheritage.org over https.

				VCS password for pushes
				~~~~~~~~~~~~~~~~~~~~~~~

				If you're not comfortable setting up SSH to upload your changes,
				you have the option of setting a VCS password.
				This password, separate from your account password,
				allows Phabricator to authenticate your uploads over HTTPS.

				In your forge User settings page (On the top right, click on your avatar,
				then click Settings), you need to use the Authentication > VCS Password
				section to set your VCS password (Direct link:
				``hxxps://forge.softwareheritage.org/settings/user/<your username>/page/vcspassword/``).

				If you still get a 403 error on push, this means you need
				a forge administrator to enable HTTPS pushes for the repository
				(which wasn't done by default in historical repositories).
				Please drop by on IRC and let us know!

				Workflow
				++++++++

				* work in a feature branch: ``git checkout -b my-feat``
				* initial review request: hack/commit/hack/commit ;
				``arc diff origin/master``
				* react to change requests: hack/commit/hack/commit ;
				``arc diff --update Dxx origin/master``
				* landing change: ``git checkout master ; git merge my-feat ; git push``

				Starting a new feature and submit it for review
				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

				Use a one branch per feature workflow, with well-separated
				logical commits (:ref:`following those conventions <git-style-guide>`).
				Please open one diff per logical commit to keep the diff size to a minimum.

				.. code-block::

				git checkout -b my-shiny-feature
				... hack hack hack ...
				git commit -m 'architecture skeleton for my-shiny-feature'
				... hack hack hack ...
				git commit -m 'my-shiny-feature: implement module foo'
				... etc ...

				Please, follow the
				To submit your code for review the first time::

				arc diff origin/master

				arc will prompt for a code review message. Provide the following information:

				* first line: short description of the overall work
				(i.e., the feature you're working on).
				This will become the title of the review
				* Summary field (optional): long description of the overall work;
				the field can continue in subsequent lines, up to the next field.
				This will become the "Summary" section of the review
				* Test Plan field (optional): write here if something special is needed
				to test your change
				* Reviewers field (optional): the (Phabricator) name(s) of
				desired reviewers.
				If you don't specify one (recommended) the default reviewers will be chosen
				* Subscribers field (optional): the (Phabricator) name(s) of people that
				will be notified about changes to this review request.
				In most cases it should be left empty

				For example::

				mercurial loader

				Summary: first stab at a mercurial loader (T329)

				The implementation follows the plan detailed in F2F discussion with @foo.

				Performances seem decent enough for a first trial (XXX seconds for YYY repository
				that contains ZZZ patches).

				Test plan:

				Reviewers:

				Subscribers: foo

				After completing the message arc will submit the review request
				and tell you its number and URL::

				[...]
				Created a new Differential revision:
				Revision URI: https://forge.softwareheritage.org/Dxx

				.. _arc-update:

				Updating your branch to reflect requested changes
				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

				Your feature might get accepted as is, YAY!
				Or, reviewers might request changes; no big deal!

				Use the Differential web UI to follow-up to received comments, if needed.

				To implement requested changes in the code, hack on your branch as usual by:

				* adding new commits, and/or
				* rewriting old commits with git rebase (to preserve a nice, easy to bisect history)
				* pulling on master and rebasing your branch against it if meanwhile someone
				landed commits on master:

				.. code-block::

				git checkout master
				git pull
				git checkout my-shiny-feature
				git rebase master


				When you're ready to update your review request::

				arc diff --update Dxx HEAD~

				Arc will prompt you for a message: describe what you've changed
				w.r.t. the previous review request, free form.
				Your message will become the changelog entry in Differential
				for this new version of the diff.

				Differential only care about the code diff, and not about the commits
				or their order.
				Therefore each "update" can be a completely different series of commits,
				possibly rewritten from the previous submission.

				Dependencies between diffs
				^^^^^^^^^^^^^^^^^^^^^^^^^^

				Note that you can manage diff dependencies within the same module
				with the following keyword in the diff description::

				Depends on Dxx

				That allows to keep a logical view in your diff.
				It's not strictly necessary (because the tooling now deals with it properly)
				but it might help reviewers or yourself to do so.

				Landing your change onto master
				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

				Once your change has been approved in Differential,
				you will be able to land it onto the master branch.

				Before doing so, you're encouraged to clean up your git commit history,
				reordering/splitting/merging commits as needed to have separate
				logical commits and an easy to bisect history.
				Update the diff :ref:`following the prior section <arc-update>`
				(It'd be good to let the ci build finish to make sure everything is still green).

				Once you're happy you can push to origin/master directly, e.g.::

				git checkout master
				git merge --ff-only my-shiny-feature
				git push

				``--ff-only`` is optional, and makes sure you don't unintentionally
				create a merge commit.

				Optionally you can then delete your local feature branch::

				git branch -d my-shiny-feature

				Reviewing locally / landing someone else's changes
				^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

				You can do local reviews of code with arc patch::

				arc patch Dxyz

				This will create a branch arcpatch-Dxyz containing the changes
				on your local checkout.

				You can then merge those changes upstream with::

				git checkout master
				git merge --ff arcpatch-Dxyz
				git push origin master

				or, alternatively::

				arc land --squash


				See also
				--------

				* :ref:`code-review` for guidelines on how code is reviewed
				when developing for Software Heritage