Upgrading a Third-Party Bundle for a Major Symfony Version
==========================================================

Symfony 3 was released in November 2015. Although this version doesn't contain
any new features, it removes all the backward compatibility layers included in
the previous 2.8 version. If your bundle uses any deprecated feature and it's
published as a third-party bundle, applications upgrading to Symfony 3 will no
longer be able to use it.

Allowing to Install Symfony 3 Components
----------------------------------------

Most third-party bundles define their Symfony dependencies using the ``~2.N`` or
``^2.N`` constraints in the ``composer.json`` file. For example:

.. code-block:: json

    {
        "require": {
            "symfony/framework-bundle": "~2.7",
            "symfony/finder": "~2.7",
            "symfony/validator": "~2.7"
        }
    }

These constraints prevent the bundle from using Symfony 3 components, which
means the bundle cannot be installed in a Symfony 3 based application. Thanks to the
flexibility of Composer dependencies constraints, you can specify more than one
major version by replacing ``~2.N`` by ``~2.N|~3.0`` (or ``^2.N`` by ``^2.N|~3.0``).

The above example can be updated to work with Symfony 3 as follows:

.. code-block:: json

    {
        "require": {
            "symfony/framework-bundle": "~2.7|~3.0",
            "symfony/finder": "~2.7|~3.0",
            "symfony/validator": "~2.7|~3.0"
        }
    }

.. tip::

    Another common version constraint found on third-party bundles is ``>=2.N``.
    You should avoid using that constraint because it's too generic (it means
    that your bundle is compatible with any future Symfony version). Use instead
    ``~2.N|~3.0`` or ``^2.N|~3.0`` to make your bundle future-proof.

Look for Deprecations and Fix Them
----------------------------------

Besides allowing users to use your bundle with Symfony 3, your bundle must stop using
any feature deprecated by the 2.8 version because they are removed in 3.0 (you'll get
exceptions or PHP errors). The easiest way to detect deprecations is to install
the `symfony/phpunit-bridge package`_ and then run the test suite.

First, install the component as a ``dev`` dependency of your bundle:

.. code-block:: terminal

    $ composer require --dev symfony/phpunit-bridge

Then, run your test suite and look for the deprecation list displayed after the
PHPUnit test report:

.. code-block:: terminal

    # this command is available after running "composer require --dev symfony/phpunit-bridge"
    $ ./bin/phpunit

    # ... PHPUnit output

    Remaining deprecation notices (3)

    The "pattern" option in file ... is deprecated since version 2.2 and will be
    removed in 3.0. Use the "path" option in the route definition instead ...

    Twig Function "form_enctype" is deprecated. Use "form_start" instead in ...

    The Symfony\Bundle\SecurityBundle\SecurityContext class is deprecated since
    version 2.6 and will be removed in 3.0. Use ...

Fix the reported deprecations, run the test suite again and repeat the process
until no deprecation usage is reported.

Useful Resources
~~~~~~~~~~~~~~~~

There are several resources that can help you detect, understand and fix the use
of deprecated features:

`Official Symfony Guide to Upgrade from 2.x to 3.0`_
    The full list of changes required to upgrade to Symfony 3.0 and grouped
    by component.
`SensioLabs DeprecationDetector`_
    It runs a static code analysis against your project's source code to find
    usages of deprecated methods, classes and interfaces. It works for any PHP
    application, but it includes special detectors for Symfony applications,
    where it can also detect usages of deprecated services.
`Symfony Upgrade Fixer`_
    It analyzes Symfony projects to find deprecations. In addition it solves
    automatically some of them thanks to the growing list of supported "fixers".

Testing your Bundle in Symfony 3
--------------------------------

Now that your bundle has removed all deprecations, it's time to test it for real
in a Symfony 3 application. Assuming that you already have a Symfony 3 application,
you can test the updated bundle locally without having to install it through
Composer.

If your operating system supports symbolic links, instead point the appropriate
vendor directory to your local bundle root directory:

.. code-block:: terminal

    $ ln -s /path/to/your/local/bundle/ vendor/you-vendor-name/your-bundle-name

If your operating system doesn't support symbolic links, you'll need to copy
your local bundle directory into the appropriate directory inside ``vendor/``.

Update the Travis CI Configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In addition to running tools locally, it's recommended to set-up Travis CI service
to run the tests of your bundle using different Symfony configurations. Use the
following recommended configuration as the starting point of your own configuration:

.. code-block:: yaml

    language: php
    php:
        - 5.3
        - 5.6
        - 7.0

    matrix:
        include:
            - php: 5.3.3
              env: COMPOSER_FLAGS='--prefer-lowest --prefer-stable' SYMFONY_DEPRECATIONS_HELPER=max[total]=999999
            - php: 5.6
              env: SYMFONY_VERSION='2.7.*'
            - php: 5.6
              env: SYMFONY_VERSION='2.8.*'
            - php: 5.6
              env: SYMFONY_VERSION='3.0.*'
            - php: 5.6
              env: SYMFONY_VERSION='3.1.*'
            - php: 5.6
              env: DEPENDENCIES='dev' SYMFONY_VERSION='3.2.*@dev'

    before_install:
        - composer self-update
        - if [ "$DEPENDENCIES" == "dev" ]; then perl -pi -e 's/^}$/,"minimum-stability":"dev"}/' composer.json; fi;
        - if [ "$SYMFONY_VERSION" != "" ]; then composer --no-update require symfony/symfony:${SYMFONY_VERSION}; fi;

    install: composer update $COMPOSER_FLAGS

    script: phpunit

Updating your Code to Support Symfony 2.x and 3.x at the Same Time
------------------------------------------------------------------

The real challenge of adding Symfony 3 support for your bundles is when you want
to support both Symfony 2.x and 3.x simultaneously using the same code. There
are some edge cases where you'll need to deal with the API differences.

Before diving into the specifics of the most common edge cases, the general
recommendation is to **not rely on the Symfony Kernel version** to decide which
code to use::

    if (Kernel::VERSION_ID < 20800) {
        // code for Symfony 2.x
    } else {
        // code for Symfony 3.x
    }

Instead of checking the Symfony Kernel version, check the version of the specific
component. For example, the OptionsResolver API changed in its 2.6 version by
adding a ``setDefined()`` method. The recommended check in this case would be::

    use Symfony\Component\OptionsResolver\OptionsResolver;

    if (!method_exists(OptionsResolver::class, 'setDefined')) {
        // code for the old OptionsResolver API
    } else {
        // code for the new OptionsResolver API
    }

.. tip::

    There is one case when you actually can rely on the
    ``Symfony\Component\HttpKernel\Kernel::VERSION_ID`` constant: when trying
    to detect the version of the ``symfony/http-kernel`` component, because it
    is the component where this constant is defined.

.. _`symfony/phpunit-bridge package`: https://github.com/symfony/phpunit-bridge
.. _`Official Symfony Guide to Upgrade from 2.x to 3.0`: https://github.com/symfony/symfony/blob/2.8/UPGRADE-3.0.md
.. _`SensioLabs DeprecationDetector`: https://github.com/sensiolabs-de/deprecation-detector
.. _`Symfony Upgrade Fixer`: https://github.com/umpirsky/Symfony-Upgrade-Fixer
