My keynote last week at Symfony Live London was about adopting a formal
release process. In fact, I've talked about adopting a shorter release
cycle for Symfony for quite some time now, and I think that this is the
right time to discuss it.
As we have all noticed, Symfony enjoys a large community of "core"
developers: a core developer being someone who contribute to Symfony on
a regular basis. The flow of pull requests has been outstanding and
steady for the past two years, and with such an activity, trying to
release often without a clear roadmap is quite difficult. Adopting a
more formal release cycle will also give more visibility to the
contributors and allow for everyone to understand when a new feature
might be available in Symfony.
So, here is my initial proposal, which is the one I've talked about
during Symfony Live and of course, it is up for discussion. I would like
to apply the new release process as soon as possible and if possible for
Symfony 2.2. And whenever we all agree on the final version of this
proposal, it will be included in the official Symfony documentation.
This release process only applies to the code hosted on the
symfony/symfony repository, but of course, I hope that third-party code
related to Symfony (like the Symfony bundles) will also adopt it (at
least, just for the timeline).
Let's list the goals for the new process:
* Shorten the release cycle;
* Keep backward compatibility as much as possible;
* Enhance the overall quality of the framework (not just the code, but
documentation, bundles, ...);
* Give more visibility to our "customers": developers using the
framework to get their job done and Open-Soure projects using/embedding
Symfony;
* Improve the experience of Symfony core contributors by controlling
the flow of incoming pull requests (why pull requests are not always
merged right away? when will a new feature be merged? when breaking BC
is acceptable? ...);
* Coordinate our timeline with projects that we are using (Doctrine,
Propel, Monolog, Assetic, Twig, ...) but also with projects that are
using/embedding Symfony;
* Give time to the Symfony ecosystem to catch up with the new versions
(bundleauthors, documentation writers, translators, ...);
* Allow developers to benefit from the new features faster.
That's a lot to take care of!
So, without further ado, here is my plan.
Timeline
--------
Historically, we've been able to release a new major version every year
since 2005. Nothing was even written about that, but that's what we did.
From now on, I propose to adopt a *time-based model* for Symfony and I
think that having a new major release every six months is a good
compromise: it gives plenty of time to work on new features but it also
allows for non-ready features to be postponed to the next version
(without having to wait too much for the next cycle).
Six months should be fast enough for developers who want to work on the
latest and the greatest; but at the same time, companies might want more
time to learn and upgrade. The way to make everyone happy is to ensure
an easy upgrade path from one version to the next one. Take Twig as an
example: I've been able to release a new major version every month and a
half since 1.0; that's very fast and it has been possible because we've
kept backward compatibility between all major releases (and of course
the scope of Twig is also smaller).
Six month releases mean that two releases fit in a year and so,
everybody knows when releases will be made without having to check on
the website: for Symfony it will be at the end of May and at the end of
November of each year. That brings predictability and visibility.
The key is keeping backward compatibility. We must be much more careful
when breaking backward compatibility; and the possibility to break
backward compatibility depends on the component we are talking about.
The following components must never break backward compatibility because
they are the low-level architecture of the framework and also because so
many people rely on them:
* ClassLoader
* Console
* DependencyInjection
* EventDispatcher
* HttpFoundation
* HttpKernel
* Routing
Backward compatibility should be easy to keep for the following components:
* BrowserKit
* CssSelector
* DomCrawler
* Filesystem
* Finder
* Locale
* OptionsResolver
* Process
* Templating
* Yaml
And these components should probably become more stable soon, but that's
not that easy (yet):
* Config
* Form
* Security
* Serializer
* Translation
* Validator
Six months can be seen as a rather short period to make a new release,
especially if we look at what we did in the past. I think we can make it
work because we have now more people able to help, but also because the
six month period itself should be cut in shorter periods:
* Development: 4 months to add new features and to enhance existing ones;
* Stabilisation: 2 months to fix bugs, prepare the release, and wait
for the whole ecosystem to catch up.
During the development phase, we can revert any new feature if we think
that we won't be able to finish it in time or if we think that it won't
be stable enough to be included.
During the stabilisation phase, some developers might still work on new
features for the next version, but it would be better if most developers
can concentrate on finishing the current version.
By the way, when I have a look at the pull requests today, I think that
we already have enough features for Symfony 2.2.
Long Term Support release
-------------------------
We've not yet published our LTS release for Symfony2. As I mentioned it
in the past, the first LTS should be Symfony 2.3.
Each LTS release will be supported for a 3 year period but it will also
be supported for at least a year after the next LTS is released. So, it
means that we are going to release a new LTS version every two years.
This dual release cycle should make everyone happy. If you are a fast
mover, you want to work with the latest and the greatest, stick with the
standard support releases: you have a new version every six months, and
you have two months to upgrade to the next one. If you are a big
company, and you want more stability, stick with the long term support
releases: you get a new version every two years and you have a year to
upgrade.
Schedule
--------
To make things more concrete, here is the schedule for the next few
versions:
* Symfony 2.2 will be released at the end of February 2013;
* Symfony 2.3 (the first LTS) will be released at the end of Mai 2013
(only 3 months after 2.2 as it will be a "special" release in the sense
that we will mainly remove the 2.0 BC layer and also because I think
that May and November are the best months for releases);
* Symfony 2.4 will be released at the end of November 2013;
* Symfony 2.5 will be released at the end of Mai 2014;
* ...
So, why not releasing Symfony 2.2 earlier as we already have so many
features waiting in the pull request queue? Because of the next section:
this is our last chance to break backward compatibility.
Symfony 3.0
-----------
After the release of Symfony 2.3, backward compatibility will be kept at
all cost. If it is not possible, the feature/enhancement will be
scheduled for Symfony 3.0. And the work on 3.0 will start whenever we
think that we have enough great features under our belt to make it worth it.
Maintenance
-----------
After Symfony 2.3, non LTS releases will be maintained for 8 months to
give people plenty of time to upgrade (keep in mind that even if no BC
breaks will have occurred, you might need to upgrade your applications
to benefit from the new features and the new best practices).
Contributions
-------------
To make the new process works well (no BC and a fixed schedule), we need
to formalise the contribution process a bit more. Every new Symfony
feature or enhancement must be worked on via Git pull requests. A few
months ago, we formalised the pull request process a bit by adding a
required
[header](http://symfony.com/doc/current/contributing/code/patches.html#make-a-pull-request)/check
list. But I've done a poor job in enforcing the rule. So, I'm going to
be uncompromising about it now and at the same time I'd like to
introduce even more checks in the list.
A pull request will only be merged if the following rules are met:
* The code is correct and it uses the Symfony way of doing things
(naming conventions, coding standards, ...);
* The new code is tested (or the bug to fix is covered by tests) and
all the tests pass on all supported PHP versions;
* The documentation has been updated (with a pending pull request on
symfony/symfony-docs);
* The changelog and upgrade files have been updated;
* No backward compatibility break has been introduced;
* If it is a fix, it has been applied to the oldest and still
supported Symfony version;
* For major features, a RFC has been written, discussed, and approved.
As I said at the beginning, this is a draft, and you are all welcome to
chime in and propose changes.
--
Fabien Potencier
Sensio CEO - Symfony lead developer
sensiolabs.com | symfony.com | fabien.potencier.org
Tél: +33 1 40 99 80 80
--
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