@title Contributing Code
@group detail

Describes how to contribute code to Phabricator.

Overview
========

If you're planning to send a patch to Phabricator, this guide can help you
through the process. The most important parts of contributing code to
Phabricator are:

  - File a task with a bug report or feature request //before// you write code.
  - We rarely accept patches which we haven't discussed first.
  - We do not accept patches against prototype applications.
  - You must sign the CLA.
  - We do not accept GitHub pull requests.
  - Some alternative approaches are available if your change isn't something
    we want to bring upstream.

The rest of this article describes these points in more detail, and then
provides guidance on writing and submitting patches.

If you just want to contribute some code but don't have a specific bug or
feature in mind, see the bottom of this document for tips on finding ways to get
started.

For general information on contributing to Phabricator, see
@{article:Contributor Introduction}.


Coordinate First
================

Before sending code, you should file a bug report or feature request describing
what you'd like to write. For details on how to do this, see these articles:

  - @{article:Contributing Bug Reports}
  - @{article:Contributing Feature Requests}

When you file a task, mention that you'd like to write the code to fix it. We
can help contextualize your request or bug and guide you through writing an
upstreamable patch, provided it's something that's upstreamable. If it isn't
upstreamable, we can let you know what the issues are and help find another
plan of attack.

You don't have to file first (for example, if you spot a misspelling it's
normally fine to just send a diff), but for anything even moderately complex
you're strongly encouraged to file first and coordinate with the upstream.


Rejecting Patches
=================

If you send us a patch without coordinating it with us first, it will probably
be immediately rejected, or sit in limbo for a long time and eventually be
rejected. The reasons we do this vary from patch to patch, but some of the most
common reasons are:

**Unjustifiable Costs**: We support code in the upstream forever. Support is
enormously expensive and takes up a huge amount of our time. The cost to support
a change over its lifetime is often 10x or 100x or 1000x greater than the cost
to write the first version of it. Many uncoordinated patches we receive are
"white elephants", which would cost much more to maintain than the value they
provide.

As an author, it may look like you're giving us free work and we're rejecting it
as too expensive, but this viewpoint doesn't align with the reality of a large
project which is actively supported by a small, experienced team. Writing code
is cheap; maintaining it is expensive.

By coordinating with us first, you can make sure the patch is something we
consider valuable enough to put long-term support resources behind, and that
you're building it in a way that we're comfortable taking over.

**Not a Good Fit**: Many patches aren't good fits for the upstream: they
implement features we simply don't want. You can find more information in
@{article:Contributing Feature Requests}. Coordinating with us first helps
make sure we're on the same page and interested in a feature.

The most common type of patch along these lines is a patch which adds new
configuration options. We consider additional configuration options to have
an exceptionally high lifetime support cost and are very unlikely to accept
them. Coordinate with us first.

**Not a Priority**: If you send us a patch against something which isn't a
priority, we probably won't have time to look at it. We don't give special
treatment to low-priority issues just because there's code written: we'd still
be spending time on something lower-priority when we could be spending it on
something higher-priority instead.

If you coordinate with us first, you can make sure your patch is in an area
of the codebase that we can prioritize.

**Overly Ambitious Patches**: Sometimes we'll get huge patches from new
contributors. These can have a lot of fundamental problems and require a huge
amount of our time to review and correct. If you're interested in contributing,
you'll have more success if you start small and learn as you go.

We can help you break a large change into smaller pieces and learn how the
codebase works as you proceed through the implementation, but only if you
coordinate with us first.

**Generality**: We often receive several feature requests which ask for similar
features, and can come up with a general approach which covers all of the use
cases. If you send us a patch for //your use case only//, the approach may be
too specific. When a cleaner and more general approach is available, we usually
prefer to pursue it.

By coordinating with us first, we can make you aware of similar use cases and
opportunities to generalize an approach. These changes are often small, but can
have a big impact on how useful a piece of code is.

**Infrastructure and Sequencing**: Sometimes patches are written against a piece
of infrastructure with major planned changes. We don't want to accept these
because they'll make the infrastructure changes more difficult to implement.

Coordinate with us first to make sure a change doesn't need to wait on other
pieces of infrastructure. We can help you identify technical blockers and
possibly guide you through resolving them if you're interested.


No Prototype Changes
====================

With rare exceptions, we do not accept patches for prototype applications for
the same reasons that we don't accept feature requests or bug reports. To learn
more about prototype applications, see
@{article:User Guide: Prototype Applications}.


You Must Sign the CLA
=====================

Before we can accept source code contributions, you need to submit a
[[ https://secure.phabricator.com/L28 | Contributor License Agreement ]]. Your
changes can not be accepted until you sign the agreement.

If you haven't signed it by the time you send changes for review, you'll be
reminded to sign it at that time.

If you're submitting work on behalf of a company (like your employer), the
company can sign the [[ https://secure.phabricator.com/L30 | Corporate
Contributor License Agreement ]] instead.

Both agreements are substantially similar to the Apache Foundation's CLAs. They
protect Phacility and users of Phabricator by making sure we have permission to
distribute your changes under an open source license.


No Pull Requests
================

We do not accept pull requests on GitHub:

  - We can not monitor who has signed CLAs on GitHub. You must sign the CLA
    to contribute, and we can't tell if you've signed it or not when you send
    us a pull request.
  - Pull requests do not get lint and unit tests run, so issues which are
    normally caught statically can slip by.
  - Phabricator is code review software, and developed using its own workflows.
    Pull requests bypass some of these workflows (for example, they will not
    trigger Herald rules to notify interested parties).
  - GitHub is not the authoritative master repository and we maintain a linear
    history, so merging pull requests is cumbersome on our end.
  - If you're comfortable enough with Phabricator to contribute to it, you
    should also be comfortable using it to submit changes.

Instead of sending a pull request, use `arc diff` to create a revision on the
upstream install. Your change will go through the normal Phabricator review
process.

(GitHub does not allow repositories to disable pull requests, which is why
it's technically possible to submit them.)


Alternatives
============

If you've written code but we're not accepting it into the upstream, some
alternative approaches include:

**Maintain a local fork.** This will require some ongoing effort to port your
changes forward when you update, but is often very reasonable for simple
changes.

**Develop as an application.** Many parts of Phabricator's infrastructure are
modular, and modularity is increasing over time. A lot of changes can be built
as external modules or applications without forking Phabricator itself. There
isn't much documentation or support for this right now, but you can look at
how other applications are implemented, and at other third-party code that
extends Phabricator.

**Rise to prominence.** We're more willing to accept borderline changes from
community members who are active, make multiple contributions, or have a history
with the project. This is not carte blanche, but distinguishing yourself can
make us feel more comfortable about supporting a change which is slightly
outside of our comfort zone.


Writing and Submitting Patches
==================

To actually submit a patch, run `arc diff` in `phabricator/`, `arcanist/`, or
`libphutil/`. When executed in these directories, `arc` should automatically
talk to the upstream install. You can add `epriestley` as a reviewer.

You should read the relevant coding convention documents before you submit a
change. If you're a new contributor, you don't need to worry about this too
much. Just try to make your code look similar to the code around it, and we
can help you through the details during review.

  - @{article:General Coding Standards} (for all languages)
  - @{article:PHP Coding Standards} (for PHP)
  - @{article:Javascript Coding Standards} (for Javascript)

In general, if you're coordinating with us first, we can usually provide
guidance on how to implement things. The other articles in this section also
provide information on how to work in the Phabricator codebase.

Not Sure Where To Get Started?
==============================

If you don't have a specific bug or feature in mind and just want to write
some code, you can try to find something simple to get started with.

Because we're usually quick to fix easy bugs and issues, we often don't have a
very good backlog of starter tasks.

You can try searching in Maniphest for tasks tagged with #easy, which might
have something, but a lot of time this list is small and the tasks on it aren't
very fun or interesting even if they aren't technically too difficult.

In general, the best way to contribute is to come to us with a problem you
encountered or something you're interested in building, and then work with us
to find a solution to it or a plan to build it. We can help turn a hacky patch
into something that's upstreamable, and you'll get a fix or feature you want.

You can also look though the rest of the open tasks for something more
substantive that you're interested in. This will give you a better chance of
finding something that's relevant to you, but many tasks are large or blocked
by other large tasks.

If you do find something, feel free to leave a comment like "I'm interested in
working on this, is this something I could reasonably help with?". We're happy
to walk through things, break larger tasks down into more detail, provide
pointers to similar changes and the right places in the codebase to get started,
and generally figure out how to attack a problem.


Next Steps
==========

Continue by:

  - returning to the @{article:Contributor Introduction}.
