silverstripe-framework/docs/en/04_Changelogs/4.0.0.md

# 4.0.0 (unreleased)

## Introduction

This version introduces many breaking changes, which in most projects can be managed through a combination
of automatic upgrade processes as well as manual code review. This document reviews these changes and will
guide developers in preparing existing 3.x code for compatibility with 4.0

* [Highlights of Major Changes](#overview)
* [Upgrading Guide](#upgrading)
  * [Standard Upgrade](#upgrading-primary)
  * [API Specific Upgrades](#upgrading-specifics)
  * [User code style upgrades](#usercode-style-upgrades)
* [API Changes](#api-changes)
  * [General and Core API](#overview-general)
  * [ORM API](#overview-orm)
  * [Filesystem API](#overview-filesystem)
  * [Template and Form API](#overview-template)
  * [i18n](#overview-i18n)
  * [Email and Mailer](#overview-mailer)
  * [SapphireTest](#overview-testing)
  * [Security](#overview-security)

## <a name="overview"></a>Highlights of major changes

* Minimum version dependencies have increased; PHP 5.5 and Internet Explorer 10 (or other modern browser)
  is required.
* All code earlier marked as deprecated for 4.0 has now been removed. See
  [deprecation documentation](/contributing/release_process) for information on code deprecation.
* All code has been migrated to follow the PSR-2 coding standard. Most significantly, all SilverStripe
 classes are now namespaced, and some have been renamed. This has major implications for
  arrangement of templates, as well as other references to classes via string literals or configuration.
  Automatic upgrading tools have been developed to cope with the bulk of these changes (see
  [upgrading notes](#upgrading)). Some classes have been rearranged so that each file contains only one class definition. It is recommended that user code follow the same convention.
  For example, page types and their controllers should longer be collated in a single file.
* Object class has been removed.
* Asset storage has been abstracted, and a new concept of `DBFile` references via database column references
  now exists in addition to references via the existing `File` dataobject. File security and protected files
  are now a core feature.
* A new front-end development process has been developed for the construction of javascript based components,
  prominently featuring ReactJS to develop highly functional CMS content areas. A new standard form schema
  API has been developed to allow back-end PHP constructed forms to scaffold themselves within ReactJS
  powered sections.
* CMS CSS has been re-developed using bootstrap 4 as a base
  ([blog post](https://www.silverstripe.org/blog/a-frameworks-framework-why-silverstripe-4-will-use-bootstrap/))
* Asset admin has been replaced with a purely ReactJS powered upgrade, and split out
  module called [asset-admin](https://github.com/silverstripe/silverstripe-asset-admin/). You'll need to add this to your `composer.json` to retain file management capabilities for your CMS authors.
* Versioning is now a much more powerful feature, with the addition of campaigns to allow batches of related
  or inter-dependent objects to be published as a single act. Dependencies between versioned objects can be
  declared using the new ownership API, so that developers can ensure that relational consistency is
  maintained during publishing. This new system can be managed via the new "Campaigns" CMS section ([blog post](https://www.silverstripe.org/blog/campaigns-in-silverstripe-4/))
* Template variable casting (e.g. `<h1>$Title</h1>`) is enforced by default, which will ensure safe HTML encode
  unless explicitly opted out.
* Themes are now configured to cascade, where you can specify a list of themes, and have the template engine
  search programatically through a prioritised list when resolving template and CSS file paths.
* Removed module path constants (e.g. `FRAMWORK_PATH`) and support for hardcoded file paths (e.g. `mysite/css/styles.css`)
* i18n Updated to use symfony/translation over zend Framework 1. Zend_Translate has been removed.
* Replaced `Zend_Cache` and the `Cache` API with a PSR-16 implementation (symfony/cache)
* _ss_environment.php files have been removed in favour of `.env` and "real" environment variables.
* admin has been moved to a new module [silverstripe/admin](https://github.com/silverstripe/silverstripe-admin).
* Behat support updated to behat 3. See the
  [behat extension](https://github.com/silverstripe/silverstripe-behat-extension) for more information.
* The `GDBackend` and `ImagickBackend` classes have been replaced by a unified `InterventionBackend` which uses the
  [intervention/image](https://github.com/intervention/image) library to power manipualations.

## <a name="upgrading"></a>Upgrading

The below sections describe how to go about updating an existing site to be prepared for upgrade to 4.0.
Most of these upgrading tasks will involve manual code review, although in some cases there are
some automated processes that users can run to

### <a name="upgrading-primary"></a>Standard Upgrade

This section describes the processes which every project upgrading to 4.0 should follow. This should be followed
as a standard first point of upgrade.

#### Upgrade references to renamed and namespaced classes

Nearly all core PHP classes have been namespaced. For example, `DataObject` is now called `SilverStripe\ORM\DataObject`.
The below tasks describe how to upgrade an existing site to remain compatible with the newly upgraded classes.

##### Using the upgrader tool to automatically upgrade

This task should be run on every upgraded project.

We have developed an [upgrader tool](https://github.com/silverstripe/silverstripe-upgrader/) to (semi-)automatically
update your 3.x code to the new naming. Here's an example how to upgrade your `mysite` folder:

```
composer global require silverstripe/upgrader
cd ~/Project/Root
~/.composer/vendor/bin/upgrade-code upgrade ./mysite --write
```

If you want to do a dry-run, omit the `--write` option to see a preview of a diff of
all changed project files.

This will resolve the majority of upgrading work, but we strongly recommend reviewing the diff
running some regression testing on your functionality. SilverStripe core classes can be referenced
in your PHP files, but also in YAML configuration and SilverStripe templates.
For a full list of renamed classes, check the `.upgrade.yml` definitions in each module.

The rename won't affect class-based permission codes or database table names.

##### Upgrade references to literal or class table names

In 3.x the class name of any DataObject matched the table name, but in 4.x all classes are namespaced, and it is
necessary to map between table and class for querying the database.

In order to ensure you are using the correct table for any class a new
[DataObjectSchema](api:SilverStripe\ORM\DataObjectSchema) service is available to manage these mappings
(see [versioned documentation](/developer_guides/model/data_model_and_orm)).

For example, the below shows how you would update a query with a hard-coded table name:

```diff
public function countDuplicates($model, $fieldToCheck)
{
	$query = new SilverStripe\ORM\Queries\SQLSelect();
+    $table = SilverStripe\ORM\DataObject::getSchema()->tableForField($model, $field);
-    $query->setFrom("\"{$model}\"");
+    $query->setFrom("\"{$table}\"");
-    $query->setWhere(["\"{$model}\".\"{$field}\"" => $model->$fieldToCheck]);
+    $query->setWhere(["\"{$table}\".\"{$field}\"" => $model->$fieldToCheck]);
    return $query->count();
}
```

##### Replacing literal strings with fully qualified class name, or ::class constant

You'll need to update any strings that represent class names and make sure they're fully
qualified. In particular, relationship definitions such as `has_one` and `has_many` will need
to be updated to refer to fully qualified class names.

In configs and with literal PHP strings it is recommended to use the php `::class` constant,
as demonstrated below.

```diff
<?php
+ use SilverStripe\ORM\DataObject;
+ use SilverStripe\Security\Member;
class MyClass extends DataObject 
{
    private static $has_one = [
    -  'Author' => 'Member',
    +  'Author' => Member::class,
    ];
}
```
 
In the context of YAML, the magic constant `::class` does not apply. Fully qualified class names must be hard coded.

```diff
-MyObject:
+My\Project\MyObject:
  property: value
```

##### Update references to literal classes to use Injector

In many places, classes namespaced in SilverStripe 4.x will still have a non-namespaced service
name that can be accessed via Injector. You should upgrade direct object constructors with
the Injector API.

E.g.

```diff
- $field = new Varchar();
+ $field = Injector::inst()->create('Varchar');
```

#### Migrate your controllers to their own files

The convention for naming controllers is now `[MyPageType]Controller`, where it used to be `[MyPageType]_Controller`. This change was made to be more compatible with the PSR-2 standards.

You can still use, for example, `Page_Controller`, but you will get a deprecation notice. It is 
best to change it to `PageController` during your upgrade process. Keep in mind any modules or
other thirdparty code that extend `PageController` are likely to assume that class exists.

By default, a controller for a page type *must* reside in the same namespace as its page. To use different logic, override `SiteTree::getControllerName()`.

#### Upgrade template locations and references

Templates are now much more strict about their locations. You can no longer put a template in an arbitrary
folder and have it be found. Case is now also checked on case-sensitive filesystems.

Either include the folder in the template name (`renderWith('MyEmail.ss')` => `renderWith('emails/MyEmail.ss')`),
move the template into the correct directory, or both. This also affects `<% include %>` statements in templates.

When using `<% include %>` template tag you should continue to leave out the `Includes` folder.
`<% include Sidebar %>` will match only match `Includes/Sidebar.ss`, not `Sidebar.ss`.
Please refer to our [template syntax](/developer_guides/templates/syntax) for details.

Core template locations have moved - if you're including or overriding these
(e.g. for FormField templates) please adjust to the new paths. The `forms` folder
no longer exists, and instead template locations will be placed in paths that match
the `SilverStripe\Forms` namespace.

#### Upgrade static config settings to `private static`

If you have some class configuration statics defined and they aren't private, 
you may find that they don't register anymore. For example, this code, taken from 
the `silverstripe/tagfield` module will no longer work in SilverStripe 4.0.

```php
public static $allowed_actions = [
    'suggest'
];
```

Changing the visibility to `private` (as per `RequestHandler::$allowed_actions` 
visibility) will make it 4.0 compatible.

```diff
-public static $allowed_actions = [
+private static $allowed_actions = [
    'suggest'
];
```

#### Upgrade module paths in file references

You should no longer rely on modules being placed in a deterministic folder (e.g. `/framework`),
and use getters on the [Module](api:SilverStripe\Core\Manifest\Module) object instead.
They expect a module composer name, followed by the module relative path, separated by a double colon. 
This prepares SilverStripe for moving modules out of the webroot at a later point.

Usage in templates:

```ss
<!-- before -->
<img src="framework/images/image.png" />
<% require css("framework/css/styles.css") %>

<!-- after -->
<img src="$ModulePath(silverstripe/framework)/image.png" />
<% require css("silverstripe/framework: css/styles.css") %>
```

Usage in Requirements:

```php
// before
Requirements::css('framework/css/styles.css');

// after
Requirements::css('silverstripe/framework: css/styles.css');
```

Usage with custom logic:

```php
// before
$moduleFilePath = FRAMEWORK_DIR . '/MyFile.php';
$baseFilePath = BASE_PATH . '/composer.json'; 
$mysiteFilePath = 'mysite/css/styles.css';
$themesFilePath = SSViewer::get_theme_folder() . '/css/styles.css';
$themeFolderPath = THEMES_DIR . '/simple';

// after
use SilverStripe\Core\Manifest\ModuleLoader;
use SilverStripe\View\ThemeResourceLoader;
$moduleFilePath = ModuleLoader::getModule('silverstripe/framework')->getRelativeResourcePath('MyFile.php');
$baseFilePath = Director::baseFolder() . '/composer.json';
$mysiteFilePath = ModuleLoader::getModule('mysite')->getRelativeResourcePath('css/styles.css');
$themesFilePath = ThemeResourceLoader::inst()->findThemedResource('css/styles.css');
$themeFolderPath = ThemeResourceLoader::inst()->getPath('simple');
```

To ensure consistency, we've also deprecated support for path constants:

 * `FRAMEWORK_DIR` and `FRAMEWORK_PATH`
 * `FRAMEWORK_ADMIN_DIR` and `FRAMEWORK_ADMIN_PATH`
 * `FRAMEWORK_ADMIN_THIRDPARTY_DIR` and `FRAMEWORK_ADMIN_THIRDPARTY_PATH`
 * `THIRDPARTY_DIR` and `THIRDPARTY_PATH`
 * `CMS_DIR` and `CMS_PATH`
 * `THEMES_DIR` and `THEMES_PATH`

### <a name="upgrading-specifics"></a>API Specific Upgrades

The below sections deal with upgrades to specific parts of various API. Projects which rely on certain
API should be upgraded as appropriate using any of the relevant processes documented below.

#### Upgrade references of SS_Log to use PSR-3 logging

One of the great changes that comes with SilverStripe 4 is the introduction of 
[PSR-3](http://www.php-fig.org/psr/psr-3/) compatible logger interfaces. This 
means we can use thirdparty services like Monolog. `SS_Log` has been replaced
with a logger which can be accessed using the LoggerInterface::class service.

For instance, code which logs errors should be upgraded as below:

```diff
-SS_Log::log('My error message', SS_Log::ERR);
+use Psr\Log\LoggerInterface;
+Injector::inst()->get(LoggerInterface::class)->error('My error message');
```

##### How to customise the default PSR-3 logger

If necessary, you may need to customise either the default logging handler, or
one of the error formatters. For example, if running unit tests you may want to
suppress errors. You can temporarily disable logging by setting a `NullHandler`

```yml
---
Name: custom-dev-logging
After: dev-logging
Only:
  environment: dev
---
# Replace default handler with null
SilverStripe\Core\Injector\Injector:
  Monolog\Handler\HandlerInterface: Monolog\Handler\NullHandler
```

Alternatively you can customise one or both of the below services:
  - `Monolog\Formatter\FormatterInterface.detailed` service, which is used for displaying
  detailed error messages useful for developers.
  - `Monolog\Formatter\FormatterInterface.friendly` service, which is used to display "error"
  page content to visitors of the site who encounter errors.

For example, a custom error page generator could be added as below:

```yml
---
Name: custom-errorpage
After:
  - '#loggingformatters'
---
SilverStripe\Core\Injector\Injector:
  Monolog\Formatter\FormatterInterface.friendly:
    class: WebDesignGroup\ShopSite\Logging\ErrorPageFormatter
```

`WebDesignGroup\ShopSite\Logging\ErrorPageFormatter` should be a class that
implements the `Monolog\Formatter\FormatterInterface` interface.

#### Upgrade `mysite/_config.php`

The globals `$database` and `$databaseConfig` are deprecated. You should upgrade your
site _config.php files to use the `.env` configuration (below).

`conf/ConfigureFromEnv.php` is also no longer used, and references to this file should be deleted.

If you need to configure database details in PHP you should configure these details via `.env` file,
or alternatively (but less recommended) use the new `DB::setConfig()` api.

The global `$project` is deprecated in favour of the configuration setting
`SilverStripe\Core\Manifest\ModuleManifest.project`.

Changes to `mysite/_config.php`:

```diff
<?php
-global $project;
-$project = 'mysite';
-include 'conf/ConfigureFromEnv.php';
```

And also add to `mysite/_config/mysite.yml`:

```yml
SilverStripe\Core\Manifest\ModuleManifest:
  project: mysite
```

#### Upgrade of `_ss_environment.php` to `.env` configuration

The php configuration `_ss_environment.php` file has been replaced in favour of a non-executable
`.env` file, which follows a syntax similar to an `.ini` file for key/value pair assignment. Like
the old php file, `.env` may be placed in either the web root, or one level above.

For example, if you have the below `_ss_environment.php` file, your `.env` would be rewritten as follows:

`_ss_environment.php`:


```php
<?php
// Environment
define('SS_ENVIRONMENT_TYPE', 'dev');
define('SS_DEFAULT_ADMIN_USERNAME', 'admin');
define('SS_DEFAULT_ADMIN_PASSWORD', 'password');
$_FILE_TO_URL_MAPPING[__DIR__] = 'http://localhost';

// Database
define('SS_DATABASE_CHOOSE_NAME', true);
define('SS_DATABASE_CLASS', 'MySQLDatabase');
define('SS_DATABASE_USERNAME', 'root');
define('SS_DATABASE_PASSWORD', '');
define('SS_DATABASE_SERVER', '127.0.0.1');
```

    
`.env`:


```
## Environment
SS_ENVIRONMENT_TYPE="dev"
SS_DEFAULT_ADMIN_USERNAME="admin"
SS_DEFAULT_ADMIN_PASSWORD="password"
SS_BASE_URL="http://localhost/"

### Database
SS_DATABASE_CHOOSE_NAME="true"
SS_DATABASE_CLASS="MySQLDatabase"
SS_DATABASE_USERNAME="root"
SS_DATABASE_PASSWORD=""
SS_DATABASE_SERVER="127.0.0.1"
```


The removal of the `_ss_environment.php` file means that conditional logic is no longer available in the environment
variable set-up process. This generally encouraged bad practice and should be avoided. If you still require conditional
logic early in the bootstrap, this is best placed in the `_config.php` files.

Note also that `$_FILE_TO_URL_MAPPING` has been removed and replaced with `SS_BASE_URL` env var.

The global values `$database` and `$databaseConfig` have been deprecated, as has `ConfigureFromEnv.php`
which is no longer necessary.

See [Environment Management docs](/getting-started/environment_management/) for full details.

#### Replace usages of Object class

Object has been superseded by a trio of traits which replace components of this legacy class:

 - Injectable: Provides `MyClass::create()` and `MyClass::singleton()`
 - Configurable: Provides `MyClass::config()`
 - Extensible: Provides all methods related to extensions (E.g. add_extension()). Note:
   All classes which use this trait MUST invoke `constructExtensions()` in its constructor.
 
In particular specific Object class usages should be replaced as below:


Upgrade subclasses


```diff
-class MyClass extends Object
-{
-}
+use SilverStripe\Core\Extensible;
+use SilverStripe\Core\Injector\Injectable;
+use SilverStripe\Core\Config\Configurable;
+class MyClass
+{
+    use Extensible;
+    use Injectable;
+    use Configurable;
+    
+    public function __construct()
+    {
+        // Only needed if using Extensible trait
+        $this->constructExtensions();
+    }
+}
```


References to $this->class

```diff
-$obj->class
+get_class($obj);

-$this->class;
+static::class;
```

Upgrade parse_class_spec()

```diff
-$spec = Object::parse_class_spec($spec);
+$spec = ClassInfo::parse_class_spec($spec);
```

Upgrade create_from_string()


```diff
-$obj = Object::create_from_string('Varchar(100)');
+$obj = Injector::inst()->create('Varchar(100)');
```

Extensions

```diff

-Object::add_extension('File', 'Versioned');
+File::add_extension(Versioned::class);
+DataObject::add_extension(File::class, Versioned::class); // alternate

-$has = Object::has_extension('File', 'Versioned');
+$has = File::has_extension(Versioned::class);
+$has = DataObject::has_extension(File::class, Versioned::class); // alternate

-$extensions = Object::get_extensions('File');
+$extensions = File::get_extensions();
+$extensions = DataObject::get_extensions(File::class); // alternate
```

#### Upgrade references to Session object

Session object is no longer statically accessible via `Session::inst()`. Instead, Session
is a member of the current request.

```diff
-public function httpSubmission($data, $form, $request)
-{
-    Session::set('loggedIn', null);
-}
+public function httpSubmission($data, $form, $request)
+{
+    $request->getSession()->set('loggedIn', null);
+}
```


In some places it may still be necessary to access the session object where no request is available.
In rare cases it is still possible to access the request of the current controller via
`Controller::curr()->getRequest()` to gain access to the current session.

#### Compatibility with the new front-end building tools

If you are using Requirements from 3.x then your scripts should continue to work as they did before.
The new front-end tooling is intended only for those wishing to customise the CMS look and feel, or behaviour.

Those wishing to customise the CMS should read about how to
[customise the admin interface](/developer_guides/customising_the_admin_interface/).

#### Upgrade static references to asset paths

All static files (images, javascript, stylesheets, fonts) used for the CMS and forms interfaces
in `framework` and `cms` have moved locations. These assets are now placed in a `client/` subfolder,
to account for a structural change where both javascript and styles are co-located in component-specific folders.
This will affect you if you have used `Requirements::block()` on files in the `framework/` or `cms/` folder.
Care should also be taken when referencing images in these folders from your own stylesheets (`url()`),
or via SilverStripe templates (`<img>` tags).

`Requirements` now throws an exception then a file is not found, rather than
failing silently, so check your `Requirements` are pointing to files that exist.

```
framework/javascript       => silverstripe-admin/client/dist/
framework/javascript/lang  => silverstripe-admin/client/lang/
framework/images           => silverstripe-admin/client/dist/images/
framework/css              => silverstripe-admin/client/dist/css/
framework/scss             => silverstripe-admin/client/src/styles/
admin/javascript/          => silverstripe-admin/client/src/
admin/javascript/src/      => silverstripe-admin/client/src/legacy/ (mostly)
admin/javascript/lang/     => silverstripe-admin/client/lang/
admin/scss/                => silverstripe-admin/client/styles/legacy/
admin/css/                 => silverstripe-admin/client/dist/css/
admin/css/screen.css       => silverstripe-admin/client/dist/css/bundle.css
admin/images/              => silverstripe-admin/client/dist/images/
admin/images/sprites/src/  => silverstripe-admin/client/src/sprites/
admin/images/sprites/dist/ => silverstripe-admin/client/dist/sprites/
admin/font/                => silverstripe-admin/client/dist/font/
```

Most JavaScript files in `framework/javascript` have been removed,
and are bundled through [Webpack](http://webpack.github.io/) into a combined file instead.
If you have referenced these files elsewhere, please consider
running the ES6 source files in `admin/client/src/legacy`
through your own transpiling and bundle process.

This also includes JavaScript i18n support, and the removal of the `i18n::js_i18n`
configuration option used in `Requirements::add_i18n_javascript()`.

SilverStripe core is moving away from `Requirements::combine_files` in favour of Webpack as of
4.0. `Requirements::combine_files` is being considered for deprecation in future versions.

All JavaScript thirdparty dependencies have either been moved to NPM (see `package.json`),
or moved into the `framework/admin/thirdparty` folder. If you are hotlinking to any
of these files, please consider packaging your own versions in your projects and modules.
For CMS modules, you can also use many library globals which the core bundles already expose
(see [Build Tooling](/contributing/build_tooling)).

One commonly linked thirdparty dependency is `jquery.js` bundled with SilverStripe:

```
framework/thirdparty/jquery/jquery.js => framework/admin/thirdparty/jquery/jquery.js
```

#### Explicit text casting is now enforced on all template variables

Now whenever a `$Variable` is used in a template, regardless of whether any casts or methods are
suffixed to the reference, it will be cast to either an explicit DBField for that field, or
the value declared by the `default_cast` on the parent object.

The default value of `default_cast` is `Text`, meaning that now many cases where a field was
left un-uncoded, this will now be safely encoded via `Convert::raw2xml`. In cases where
un-cast fields were used to place raw HTML into templates, this will now encode this until
explicitly cast for that field.

You can resolve this in your model by adding an explicit cast to HTML for those fields.

Before:

```php
use SilverStripe\View\ViewableData;
use SilverStripe\Core\Convert;

class MyObject extends ViewableData
{
	public function getSomeHTML
	{
		$title = Convert::raw2xml($this->Title);
		return "<h1>{$title}</h1>";
	}
}
```

After:

```php
class MyObject extends SilverStripe\View\ViewableData
{
	private static $casting = [
		'SomeHTML' => 'HTMLText'
	];

	public function getSomeHTML
    {
		$title = SilverStripe\Core\Convert::raw2xml($this->Title);
		return "<h1>{$title}</h1>";
	}
}
```

If you need to encode a field (such as HTMLText) for use in html attributes, use `.ATT`
instead, or if used in an actual XML file use `.CDATA` (see [template casting](/developer_guides/templates/casting)).

#### Upgrade code that uses SQLQuery

Where your code once used SQLQuery you should now use SQLSelect in all cases, as this has been removed (check the [3.2.0](3.2.0) upgrading notes).

#### Upgrade code that uses UploadField

This field has been superceded by a new class provided by the
[asset-admin](https://github.com/silverstripe/silverstripe-asset-admin) module, which provides a more
streamlined simpler mechanism for uploading File dataobjects.

A helper service `FileHandleField` is provided to assist with dependency injection. Where the asset-admin
module is not installed this service will fall back to the `FileField` class instead.
Usages of UploadField will need to be upgraded as below.

Before:

```php
class MyClass extends DataObject
{
    public function getCMSFields()
    {
        return new FieldList(
            new UploadField('Files')
        );
    }
}
```


After:

```php
use SilverStripe\ORM\DataObject;
use SilverStripe\Forms\FieldList;
use SilverStripe\Forms\FileHandleField;

class MyClass extends DataObject
{
    public function getCMSFields()
    {
        return FieldList::create(
            Injector::inst()->create(FileHandleField::class, 'Files')
        );
    }
}
```

#### Upgrade code that uses i18n

In many cases, localisation strings which worked in 3.x will continue to work in 4.0, however certain patterns
have been deprecated and will be removed in 5.0. These include:

 - _t calls with sprintf-style placeholders (`%s`). Replace with named placeholders instead.
 - _t calls with non-associative injection arguments. Please use an associative array for all arguments.
 - _t calls which do not include a default value will now raise a warning. This can be disabled by setting
   the `i18n.missing_default_warning` config to false.
 
Note: If you attempt to use non-associative injection arguments with named placeholders, the result will
now trigger an exception.

Implementors of i18nEntityProvider should note that the return type for provideI18nEntities() has changed as well.
The non-associative array return type is deprecated. If returning a default string for a module
other than itself, it should return an array with the `default` and `module` keys respectively.

Full locale-rule respecting localisation for plural forms is now supported. The default
key for an object plural form is `<Namespaced\ClassName>.PLURALS`, and follows CLDR array form for each
pluralisation. See [the CLDR chart](http://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html)
for reference.

The below demonstrates how you can provide new localisation strings for an object,
including both plurals and cross-module localisations.


```php
class MyObject extends DataObject, implements i18nEntityProvider
{
    public function provideI18nEntities()
    {
        return [
            'MyObject.SINGULAR_NAME' => 'object',
            'MyObject.PLURAL_NAME' => 'objects',
            'MyObject.PLURALS' => [
                'one' => 'An object',
                'other' => '{count} objects',
            ],
            'AnotherSection.DESCRIPTION' => [
                'default' => 'This is the description for this section',
                'module' => 'extendedmodule',
            ],
        ];
    }
}
```


In YML format this will be expressed as the below:

`mymodule/lang/en.yml`:


```yml
en:
  MyObject:
    SINGULAR_NAME: 'object'
    PLURAL_NAME: 'objects'
    PLURALS:
      one: 'An object',
      other: '{count} objects'
```

`extendedmodule/lang/en.yml`:


```yml
en:
  AnotherSection:
    DESCRIPTION: 'This is the description for this section'
```


Usage of these pluralised strings is through the existing _t() method,
and require a `|` pipe-delimeter with a {count} argument.


```php
public function pluralise($count)
{
    return _t('MyObject.PLURALS', 'An object|{count} objects', [ 'count' => $count ]);
}
```

In templates this can also be invoked as below:


```ss
<%t MyObject.PLURALS 'An item|{count} items' count=$Count %>
```

#### Removed Member.DateFormat and Member.TimeFormat database settings

We're using [native HTML5 date and time pickers](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/date)
in `DateField` and `TimeField` now ([discussion](https://github.com/silverstripe/silverstripe-framework/issues/6626)),
where the browser localises the output based on the browser/system preferences.
In this context it no longer makes sense to give users control over their own
date and time formats in their CMS profile. 
Consequently, we've also removed `MemberDatetimeOptionsetField`.
 
`Member->getDateFormat()` and `Member->getTimeFormat()` still exist, and default to
the [IntlDateFormatter defaults](http://php.net/manual/en/class.intldateformatter.php) for the selected locale.


#### New asset storage mechanism

File system has been abstracted into an abstract interface. By default, the out of the box filesystem
uses [Flysystem](http://flysystem.thephpleague.com/) with a local storage mechanism (under the assets directory).

Because the filesystem now uses the sha1 of file contents in order to version multiple versions under the same
filename, the default storage paths in 4.0 will not be the same as in 3.

In order to retain existing file paths in line with framework version 3 you should set the
`\SilverStripe\Filesystem\Flysystem\FlysystemAssetStore.legacy_paths` config to true.
Note that this will not allow you to utilise certain file versioning features in 4.0.


```yml
SilverStripe\Filesystem\Flysystem\FlysystemAssetStore:
  legacy_paths: true
```


See our ["File Management" guide](/developer_guides/files/file_management) for more information.

#### Migrating File DataObject from 3.x to 4.0

Since the structure of `File` dataobjects has changed, a new task `MigrateFileTask` has been added to assist
in migration of legacy files. Migration can be invoked by either this task, or can be configured to automatically
run during dev build by setting the `File.migrate_legacy_file` config to true. However, it's recommended that
this task is run manually during an explicit migration process, as this process could potentially consume
large amounts of memory and run for an extended time.


```yml
File:
  migrate_legacy_file: true
```

This task will also support migration of existing File DataObjects to file versioning. Any
pre-existing File DataObjects will be automatically published to the live stage, to ensure
that previously visible assets remain visible to the public site.

If additional security or visibility rules should be applied to File dataobjects, then
make sure to correctly extend `canView` via extensions.

Note that pre-existing security solutions for 3.x (such as
[secure assets module](https://github.com/silverstripe/silverstripe-secureassets))
are incompatible with core file security.


#### Upgrade code which acts on `Image`

As all image-specific manipulations has been refactored from `Image` into an `ImageManipulations` trait, which
is applied to both `File` and `DBFile`. These both implement a common interface `AssetContainer`, which
has the `getIsImage()` method. In some cases, it may be preferable to invoke this method to detect
if the asset is an image or not, rather than checking the subclass, as the asset may also be a `DBFile` with
an image filter applied, rather than an instance of the `Image` dataobject.

In addition, a new file category `image/supported` has been added, which is a subset of the `image` category.
This is the subset of all image types which may be assigned to the `[Image](api:SilverStripe\Assets\Image)` dataobject, and may have
manipulations applied to it. This should be used as the file type restriction on any `[UploadField](api:SilverStripe\AssetAdmin\Forms\UploadField)` which
is intended to upload images for manipulation.

```diff
-if($file instanceof Image) {
-	$upload = new UploadField();
-	$upload->setAllowedFileCategories('image');
-}
+if ($file->getIsImage()) {
+	$upload = new UploadField();
+	$upload->setAllowedFileCategories('image/supported');
+}
```

In cases where image-only assets may be assigned to relationships then your datamodel should specify explicitly
an `Image` datatype, or refer to `DBFile('image/supported')`.

```php
class MyObject extends SilverStripe\ORM\DataObject
{
	private static $has_one = [
		"ImageObject" => "Image"
	];
	private static $db = [
		"ImageField" => "DBFile('image/supported')"
	];
}
```

#### Upgrading code that writes to `File` dataobjects, or writes files to the 'assets' folder

In the past all that was necessary to write a `File` DataObject to the database was to ensure a physical file
existed in the assets folder, and that the Filename of the DataObject was set to the same location.

Since the storage of physical files is no longer a standard location, it's necessary to delegate the writing of such
files to the asset persistence layer. As a wrapper for an individual file, you can use any of the `setFrom*`
methods to assign content from a local (e.g. temporary) file, a stream, or a string of content.
You would need to upgrade your code as below.

```diff
-function importTempFile($tmp)
-{
-	copy($tmp, ASSETS_PATH . '/imported/' . basename($tmp));
-	$file = new File();
-	$file->setFilename('assets/imported/'.basename($tmp));
-	$file->write();
-}
+public function importTempFile($tmp)
+{
+   Versioned::reading_stage('Stage');
+   $file = new File();
+   $file->setFromLocalFile($tmp, 'imported/' . basename($tmp));
+	$file->write();
+	$file->doPublish();
+}
```

Note that 'assets' is no longer present in the new code, and the path beneath what was once assets is now
used to generate the 'filename' value. This is because there is no longer an assumption that files are
stored in the assets folder.

There are other important considerations in working with File dataobjects which differ from legacy:

* File synchronisation is no longer automatic. This is due to the fact that there is no longer a 1-to-1 relationship
  between physical files and File DataObjects.
* Folder DataObjects are now purely logical DataObjects, and perform no actual filesystem folder creation on write.
* All Files are versioned, which means that by default, new File records will not be visibile
  to the public site. You will need to make sure to invoke `->doPublish()` on any File DataObject
  you wish visitors to be able to see.

You can disable File versioning by adding the following to your `_config.php`

```php
SilverStripe\Assets\File::remove_extension('Versioned');
```

#### Upgrading code performs custom image manipulations

As file storage and handling has been refactored into the abstract interface, many other components which were
once specific to Image.php have now been moved into a shared `ImageManipulation` trait. Manipulations of file content,
which are used to generate what are now called "variants" of assets, is now a generic api available to both `File`
and `DBFile` classes through this trait.

Custom manipulations, applied via extensions, must be modified to use the new API.
For instance, code which sizes images to a fixed width should be updated as below:

Before:

```php
// in MyImageExtension.php
class MyImageExtension extends SilverStripe\ORM\DataExtension
{
	public function GalleryThumbnail($height)
    {
		return $this->getFormattedImage('GalleryThumbnail', $height);
	}

	public function generateGalleryThumbnail(Image_Backend $backend, $height)
    {
		return $backend->paddedResize(300, $height);
	}
}

// in _config.php
SilverStripe\Assets\Image::add_extension('MyImageExtension');
```

Now image manipulations are implemented with a single method via a callback generator:

```php
// in MyImageExtension.php
class MyImageExtension extends SilverStripe\Core\Extension
{
	public function GalleryThumbnail($height)
    {
		// Generates the manipulation key
		$variant = $this->owner->variantName(__FUNCTION__, $height);

		// Instruct the backend to search for an existing variant with this key,
		// and include a callback used to generate this image if it doesn't exist
		return $this->owner->manipulateImage($variant, function (Image_Backend $backend) use ($height) {
			return $backend->paddedResize(300, $height);
		});
	}
}

// in _config.php
File::add_extension('MyImageExtension');
\SilverStripe\Filesystem\Storage\DBFile::add_extension('MyImageExtension');
```

There are a few differences in this new API:

* The extension is no longer specific to DataObjects, so it uses the generic `Extension` class instead of `DataExtension`
* This extension is added to both `DBFile` and `File`, or order to make this manipulation available to non-dataobject
  file references as well, but it could be applied to either independently.
* A helper method `variantName` is invoked in order to help generate a unique variant key. Custom code may use another
  generation mechanism.
* Non-image files may also have manipulations, however the specific `manipulateImage` should not be used in this case.
  A generic `manipulate` method may be used, although the callback for this method both is given, and should return,
  an `AssetStore` instance and file tuple (Filename, Hash, and Variant) rather than an Image_Backend.

#### Upgrading code that uses File or Image shortcode handler

The `handle_shortcode` methods have been removed from the core File and Image classes and moved to separate classes in their own respective namespace. Image and File do not implement the ShortcodeHandler interface anymore.

The shortcode handler for `File` has been moved to `SilverStripe\Assets\ShortcodesFileShortcodeProvider` and the Image handler has been moved to `SilverStripe\Assets\Shortcodes\ImageShortcodeProvider`

Before this change, to use the handle_shortcode method, you would do something like this:

```
<?php

class MyShortcodeUser extends Object {


	private $content;

    public function Content($arguments, $parser, $shortcode) {
        return File::handle_shortcode($arguments, $this->content, $parser, $shortcode);
    }
}
```

In the new situation, this would look like this:

```
<?php 

use SilverStripe\Assets\Shortcodes\FileShortcodeProvider;

class MyShortcodeUser extends Object {

	private $content;

    public function Content($arguments, $parser, $shortcode) {
        return FileShortcodeProvider::handle_shortcode($arguments, $this->content, $parser, $shortcode);
    }
}
```

#### Upgrading code that uses composite db fields.

The `CompositeDBField` interface has been replaced with an abstract class, `DBComposite`. In many cases, custom code
that handled saving of content into composite fields can be removed, as it is now handled by the base class.

The below describes the minimum amount of effort required to implement a composite DB field.

```php
<?php
use SilverStripe\ORM\FieldType\DBComposite;

class MyAddressField extends DBComposite
{
	private static $composite_db = [
		'Street' => 'Varchar(200)',
		'Suburb' => 'Varchar(100)',
		'City' => 'Varchar(100)',
		'Country' => 'Varchar(100)'
	];

	public function scaffoldFormField($title = null, $params = null)
    {
		new SilverStripe\Forms\TextField($this->getName(), $title);
	}
}
```

#### Upgrading code that references `DataObject::database_fields` or `DataObject::db`

These methods have been updated to include base fields (such as ID, ClassName, Created, and LastEdited), as
well as composite DB fields.

`DataObject::database_fields` does not have a second parameter anymore, and can be called directly on an object
or class. E.g. `Member::database_fields()`.
If user code requires the list of fields excluding base fields, then use custom_database_fields instead, or
make sure to call `unset($fields['ID']);` if this field should be excluded.

`DataObject:db()` will return all logical fields, including foreign key ids and composite DB Fields, alongside
any child fields of these composites. This method can now take a second parameter $includesTable, which
when set to true (with a field name as the first parameter), will also include the table prefix in
`Table.ClassName(args)` format.


#### Upgrade code that uses SQLQuery

SQLQuery is still implemented, but now extends the new SQLSelect class and has some methods
deprecated. Previously this class was used for both selecting and deleting, but these
have been superceded by the specialised SQLSelect and SQLDelete classes.

Take care for any code or functions which expect an object of type `SQLQuery`, as
these references should be replaced with `SQLSelect`. Legacy code which generates
`SQLQuery` can still communicate with new code that expects `SQLSelect` as it is a
subclass of `SQLSelect`, but the inverse is not true.

#### Upgrade BuildTask classes

Similarly to the `$table_name` configuration property for DataObjects, you should define a `private static $segment` for `BuildTask`
instances to ensure that you can still run your task via `sake dev/tasks/MyTask`. Without defining it, the default
will be a fully-qualified class name like `sake dev/tasks/Me-MyModule-Tasks-MyTask`. This can also be configured in YAML.

```php
use SilverStripe\Dev\BuildTask;

class MyTask extends BuildTask
{
    private static $segment = 'MyTask';
}
```

#### Upgrade implementations of augmentSQL

Since this method now takes a `SQLSelect` as a first parameter, existing code referencing the deprecated `SQLQuery`
type will raise a PHP error.

Before:

```php
function augmentSQL(SQLQuery &$query, DataQuery &$dataQuery = null)
{
	$locale = Translatable::get_current_locale();
	if(!preg_match('/("|\'|`)Locale("|\'|`)/', implode(' ', $query->getWhere()))) {
		$qry = sprintf('"Locale" = \'%s\'', Convert::raw2sql($locale));
		$query->addWhere($qry);
	}
}
```

After:

```php
public function augmentSQL(SQLSelect $query, DataQuery $dataQuery = null)
{
	$locale = Translatable::get_current_locale();
	if (!preg_match('/("|\'|`)Locale("|\'|`)/', implode(' ', $query->getWhereParameterised($parameters))))  {
		$query->addWhere([
			'"Locale"' => $locale
		]);
	}
}
```

#### Moved ErrorPage into a new module

ErrorPage has been moved to a separate [silverstripe/errorpage module](http://addons.silverstripe.org/add-ons/silverstripe/errorpage)
to allow for alternative approaches to managing error responses.
The module is installed by default on new projects, but needs to be added to existing projects
to preserve functionality on the existing "Page not found" and "Server error" pages in the CMS.

    composer require silverstripe/errorpage

Alternatively you can implement your own `onBeforeHTTPError()` handling to present custom errors.
By default, SilverStripe will display a plaintext "not found" message when the module isn't installed.
Check the [module upgrading guide](http://addons.silverstripe.org/add-ons/silverstripe/errorpage)
for more configuration API changes on the `ErrorPage` class.

#### Upgrading asset web.config, .htaccess, or other server configuration

Server configuration files for `/assets` are no longer static, and are regenerated via a set of
standard SilverStripe templates on flush. These templates include:

 * `Assets_HTAccess.ss`: Template for public permissions on the Apache server.
 * `Assets_WebConfig.ss`: Template for public permissions on the IIS server.
 * `Protected_HTAccess.ss`: Template for the protected store on the Apache server (should deny all requests).
 * `Protected_WebConfig.ss`: Template for the protected store on the IIS server (should deny all requests).

You will need to make sure that these files are writable via the web server, and that any necessary
configuration customisation is done via overriding these templates.

If upgrading from an existing installation, make sure to invoke `?flush=all` at least once.

See our ["File Security" guide](/developer_guides/files/file_security) for more information.

#### `ListboxField` is now multiple-only

Previously, this field would operate as either a single select (default) or multi-select by setting
`setMultiple` to either true or false.

Now this field should only be used for multi-selection. Single-selection should be done using
a regular `DropdownField`.

#### `GroupedDropdownField::setDisabled` now only accepts a list of values.

Where previously you could specify a list of grouped values in the same way as `setSource`, this
method now only accepts either a non-associative array of values (not titles) or an `SS_List`
of items to disable.

#### Upgrading TinyMCE to 4.0

Please see the [tinymce upgrading guide](http://archive.tinymce.com/wiki.php/Tutorial:Migration_guide_from_3.x)
to assist with upgrades to customisations to tinymce 3.

In Framework 4.0 the user interface for TinyMCE has been trimmed down considerably, with certain toolbar
buttons removed from the default cms configuration. These include:

 * Strikethrough
 * Styles dropdown
 * Block quotes
 * Horizontal Rule
 * Undo / Redo
 * Cut / Paste as word
 * Select all
 * Fullscreen

However, these function may be enabled on a case by case basis through modifification of the default
tinymce config, or by creating custom configurations.

The optional `ss_macron` plugin for inserting Māori diacritical marks
has been removed from core. You can configure the built-in `charmap` plugin instead:

```php
$editor = SilverStripe\Forms\HTMLEditor\HtmlEditorConfig::get('cms');
$editor->enablePlugins('charmap');
$editor->addButtonsToLine(1, 'charmap');
$editor->setOption('charmap_append', [
    ['256','A - macron'],
    ['274','E - macron'],
    ['298','I - macron'],
    ['332','O - macron'],
    ['362','U - macron'],
    ['257','a - macron'],
    ['275','e - macron'],
    ['299','i - macron'],
    ['333','o - macron'],
    ['363','u - macron']
]);
```

For more information on available options and plugins please refer to the
[TinyMCE documentation](https://www.tinymce.com/docs/configure/)

#### Upgrading DataObjects with the `Versioned` extension

In most cases, versioned models with the default versioning parameters will not need to be changed. However,
there are now additional restrictions on the use of custom stage names.

Rather than declaring the list of stages a model has, the constructor for `Versioned` will take a single mode
parameter, which declares whether or not the model is versioned and has a draft and live stage, or alternatively
if it only has versioning without staging.

```php
/**
 * This model has staging and versioning. Stages will be "Stage" and "Live"
 */
class MyStagedModel extends SilverStripe\ORM\DataObject
{
	private staic $extensions = [
		"SilverStripe\\ORM\\Versioning\\Versioned('StagedVersioned')"
	];
}

/**
 * This model has versioning only, and will not has a draft or live stage, nor be affected by the current stage.
 */
class MyVersionedModel extends DataObject
{
	private static $extensions = [
		"SilverStripe\\ORM\\Versioning\\Versioned('Versioned')"
	];
}
```

Additionally, the following api methods have been added:

 * `Versioned::publishRecursive` Publishes this object, and all owned objects
 * `Versioned::publishSingle` Publishes this object, but not owned objects
 * `Versioned::copyVersionToStage` Replaces the old `publish` method.

These methods are deprecated:

 * `Versioned::publish` Replaced by `Versioned::copyVersionToStage`
 * `Versioned::doPublish` Replaced by `Versioned::publishRecursive`

#### Implementation of ownership API

In order to support the recursive publishing of dataobjects, a new API has been developed to allow
developers to declare dependencies between objects. This is done to ensure that the published state
of linked components are consistent with their "owner." Without the concept of ownership, these linked
components could be implicitly exposed on the frontend, which may not align with the intent of the
content author.

For instance, on a products page which has a list of products, the products should not be published unless the products page is, too. The ownership API solves this by allowing you to declare
 a two-way relationship between objects, typically, but not necessarily, linked by a database relationship
 (`has_many`, `many_many`, etc.).

```php
class ProductPage extends Page 
{
    private static $has_many = [
        'Products' => Product::class
    ];
    
    private static $owns = [
        'Products'
    ];
}

class Product extends DataObject 
{
    private static $extensions = [
        Versioned::class
    ];
    
    private static $has_one = [
        'Parent' => ProductPage::class
    ];
}
```
If your objects are linked by something other than a database relationship, for instance, a custom
getter that is computed at runtime, the same rules can be applied, as long as you provide an `$owned_by`
setting on the child object.

For more information, see the [DataObject ownership](https://docs.silverstripe.org/en/4/developer_guides/model/versioning/#dataobject-ownership) documentation and the [versioning](/developer_guides/model/versioning) documentation

#### ChangeSet batch publishing

ChangeSet objects have been added, which allow groups of objects to be published in
a single atomic transaction.
This API will utilise the ownership API to ensure that changes to any object include
all necessary changes to owners or owned entities within the same changeset.

#### New `[image]` shortcode in `HTMLText` fields

The new Ownership API relies on relationships between objects.
Many of these relationships are already made explicit through `has_one`, `has_many` and `many_many`.
Images inserted into `HTMLText` fields (through a WYSIWYG editor) need to be tracked as well.
Instead of `<img>` tags, the field will insert `[image]` shortcodes which point to the database identifier
of the `Image` record rather than its path on the filesystem. The shortcode will be automatically replaced
when the field is rendered. Newly inserted images will automatically receive the shortcode and ownership tracking,
and existing `<img>` will continue to work.

#### Upgrading references to DBField and subclasses

A major change in 4.0 is the introduction of namespaced DBField subclasses. Now as a standard, all DBField subclasses have a `DB` prefix, are namespaced, and have an associative alias which omits the DB prefix.

This means that for the most part, code that worked in 3.0 won't need to be changed, although if you have any hard class literals which reference the old classes, they will need to be updated to point to the new namespaced classes.

An exception to this is any classes which once had the `SS_` prefix, which will now be instead prefixed with `DB`, and have an un-aliased prefix. For example `SS_Datetime` is now `DBDateTime`, and has the alias `DateTime` which may be used in config.

Before:

```php
use SilverStripe\ORM\DataObject;

class MyObject extends DataObject
{
    private static $db = [
        'Number' => 'Int',
        'Time' => 'SS_Datetime'
    ];

    /**
     * @param Int $val
     * @return Varchar
     */
    public function TextNumber()
    {
        return new Varchar('TextNumber', 'Number is ' . $this->Number);
    }
}
```

After:

```php
use SilverStripe\ORM\DataObject;
use SilverStripe\ORM\FieldType\DBVarchar;

class MyObject extends DataObject
{
    private static $db = [
        'Number' => 'Int',
        'Time' => 'Datetime'
    ];

    /**
     * @param Int $val
     * @return Varchar
     */
    public function TextNumber()
    {
        return new DBVarchar('TextNumber', 'Number is ' . $this->Number);
    }
}
```

Note that string references to `SS_Datetime` passed to injector, or used in config values, will still work, and will refer to the updated class names.

#### Upgrading from deprecated RestfulService

Install Guzzle to get an API consuming library.
`composer require guzzlehttp/guzzle` or add `guzzlehttp/guzzle: "^6.0"` to your composer.json.

For information on how to use Guzzle, please see the extensive [Guzzle documentation](http://docs.guzzlephp.org/en/latest/)

In case you want to keep using RestfulService, you can use `Firesphere/silverstripe-restfulservice`, but it is unmaintained and deprecated.

#### Upgrading from deprecated Oembed

Instead of Oembed, the framework now relies on [oscarotero/Embed](https://github.com/oscarotero/Embed) to handle getting the shortcode-data for embedding.
If you have custom embedding-code relying on Oembed, please refer to the documentation provided by oscarotero.

#### Admin URL can now be configured via custom Director routing rule

The default `admin/` URL to access the CMS interface can now be changed via a custom Director routing rule for
`AdminRootController`. If your website or module has hard coded `admin` URLs in PHP, templates or JavaScript, make sure
to update those with the appropriate function or config call. See
[CMS architecture](/developer_guides/customising_the_admin_interface/cms-architecture#the-admin-url) for language
specific functions.

#### Upgrading custom Authenticators

The methods `register` and `unregister` on `Authenticator` are deprecated in favor of the `Config` system. This means that any custom Authenticator needs to be registered through the yml config:

```yml
SilverStripe\Security\Authenticator;
  authenticators:
    - MyVendor\MyModule\MyAuthenticator
```

If there is no authenticator registered, `Authenticator` will try to fall back on the `default_authenticator`, which can be changed using the following config, replacing the MemberAuthenticator with your authenticator:

```yml
SilverStripe\Security\Authenticator:
  default_authenticator: SilverStripe\Security\MemberAuthenticator
```

As soon as a custom authenticator is registered, the default authenticator will not be available anymore, unless enabled specifically in the config.

By default, the `SilverStripe\Security\MemberAuthenticator` is seen as the default authenticator until it's explicitly set in the config.

#### Upgrading Config API usages

Performance optimisations have been made to Config which, under certain circumstances, require developer
care when modifying or caching config values. The top level config object is now immutable on application
bootstrap, and requires a developer to invoke `Config::modify()` to make mutable prior to modification.
This will immediately have a slight performance hit, so should be done sparingly, and avoided at all
if possible in performance intensive applications.

In addition, the `Config::inst()->update()` method is deprecated, and replaced with `Config::modify()->set()` and
`Config::modify()->merge()` to respectively replace and merge config.

When config is merged (either via modification or merged between yml blocks) falsey-values (including nulls)
now replace any prior values (even arrays).

One removed feature is the `Config::FIRST_SET` option. Either use uninherited config directly on the class
directly, or use the inherited config lookup. As falsey values now overwrite all parent class values, it is
now generally safer to use the default inherited config, where in the past you would need to use `FIRST_SET`.

#### Upgrading Cache API

We have replaced the unsupported `Zend_Cache` library with [symfony/cache](https://github.com/symfony/cache).
This also allowed us to remove SilverStripe's `Cache` API and use dependency injection with a standard
[PSR-16](http://www.php-fig.org/psr/psr-16/) cache interface instead.

Caches should be retrieved through `Injector` instead of `Cache::factory()`,
and have a slightly different API (e.g. `set()` instead of `save()`).

```diff
-$cache = Cache::factory('myCache');
+use Psr\SimpleCache\CacheInterface;
+$cache = Injector::inst()->get(CacheInterface::class . '.myCache');
 
// create a new item by trying to get it from the cache
-$myValue = $cache->load('myCacheKey');
+$myValue = $cache->get('myCacheKey');

// set a value and save it via the adapter
-$cache->save(1234, 'myCacheKey');
+$cache->set('myCacheKey', 1234);

// retrieve the cache item
-if (!$cache->load('myCacheKey')) {
-    // ... item does not exists in the cache
-}
+if (!$cache->has('myCacheKey')) {
+    // ... item does not exists in the cache
+}

// Remove a cache key
-$cache->remove('myCacheKey');
+$cache->delete('myCacheKey');
```

With the necessary minimal config in _config/mycache.yml

```yml
---
Name: mycache
---
SilverStripe\Core\Injector\Injector:
  Psr\SimpleCache\CacheInterface.myCache:
    factory: SilverStripe\Core\Cache\CacheFactory
    constructor:
      namespace: 'mycache'
```

##### Configuration Changes

Caches are now configured through dependency injection services instead of PHP.
See our ["Caching" docs](/developer-guides/performance/caching) for more details.
 
Before (mysite/_config.php):

```php
Cache::add_backend(
    'primary_memcached', 
    'Memcached',
    [
        'servers' => [
            'host' => 'localhost', 
            'port' => 11211, 
        ]
    ]
);
Cache::pick_backend('primary_memcached', 'any', 10);
```

After (mysite/_config/config.yml):

```yml
---
After:
  - '#corecache'
---
SilverStripe\Core\Injector\Injector:
  MemcachedClient:
    class: 'Memcached'
    calls:
      - [ addServer, [ 'localhost', 11211 ] ]
  SilverStripe\Core\Cache\CacheFactory:
    class: 'SilverStripe\Core\Cache\MemcachedCacheFactory'
    constructor:
      client: '%$MemcachedClient
```

### <a name="usercode-style-upgrades"></a>User-code style upgrades

Although it is not mandatory to upgrade project code to follow SilverStripe and 
PSR-2 standard it is highly recommended to ensure that code is consistent. The below sections
will assist you with bringing yourself up to speed.

Please note that before upgrading user code style it is necessary to run the standard upgrade path
to fix references and usages of framework API.

#### Upgrading user-code to use namespaces

Upgrading code to use namespaces is quite a complex process, and as such we have provided
several development tools and processes to help make the upgrade user friendly and as
automated as possible.

##### Using the upgrader tool to automatically apply namespaces

The [upgrader tool](https://github.com/silverstripe/silverstripe-upgrader/) provides a feature
to not only automatically namespace code, but will provide automatic upgrade of other code
references to those classes.

Use the below to setup upgrader, and apply a namespace to a given code folder.

```
composer global require silverstripe/upgrader
cd ~/Project/Root
~/.composer/vendor/bin/upgrade-code add-namespace "WebDesignGroup\ShopSite" ./mysite/code --recursive --write
```

If you want to do a dry-run, omit the `--write` option to see a preview of a diff of
all changed project files.

This task will do the following:

 - Add the given namespace to all files in the code class, and subdirectories.
 - Sub-namespaces will be applied based on directory structure
 - All references to classes in any namespaced files will be safely retained with additional `use` directives
  added as necessary.
 - Register all namespaced classese in a mysite/.upgrade.yml file for migration of other code
  
This task will not do the following, and must be done manually:

 - Adding `table_name` to any namespaced classes
 - Upgrade other references to namespaced classes outside of this folder
 - Migrate any database table records
 
Please see the following steps for more information.

##### Using the upgrader tool to update references to namespaced user classes

Once a project has been namespaced all newly renamed classes will have a mapping included in the `mysite/.upgrade.yml`
file. If you have any user-code that references these, you may need to run the upgrader again (as you did did
to upgrade your project to namespaced framework classe).

```
composer global require silverstripe/upgrader
cd ~/Project/Root
~/.composer/vendor/bin/upgrade-code upgrade ./othercode --write
``` 

##### Updating custom dataobjects to use existing table names

Once you have namespaced your user code it will be necessary to customise the `table_name` config
for your dataobjects, in order to ensure the correct table is used after upgrade. It is recommended
to point this to the base name of the class, excluding namespace, as in 3.x.

```diff
namespace WebDesignGroup\ShopSite;
use SilverStripe\ORM\DataObject;
use Page;
class GalleryPage extends Page
{
+    private static $table_name = 'GalleryPage';
}
```

##### Class name remapping

If you've namespaced one of your custom page types, you may notice a message in the CMS 
telling you it's obsolete. This is likely because the `ClassName` 
field in the `SiteTree` table still contains the singular model name, e.g. `GalleryPage`
and that when you change it to `WebDesignGroup\ShopSite\GalleryPage` then everything 
works again.

The `dev/build` task is configured to look for a legacy class name mapping 
configuration setting and will update this for you automatically. You can use
this to add DB upgrading rules for your own classes.

For example, you could upgrade references to the newly namespaced Banner class by adding
this to your `mysite/_config/upgrade.yml` file:

```yml
SilverStripe\ORM\DatabaseAdmin:
  classname_value_remapping:
    GalleryPage: WebDesignGroup\ShopSite\GalleryPage 
```

The next time you run a dev/build the class name for all `GalleryPage` pages will
be automatically updated to the new `WebDesignGroup\ShopSite\GalleryPage`

#### Using php code checker to automatically update to PSR-2

You can use the [php codesniffer](https://github.com/squizlabs/PHP_CodeSniffer) tool
to not only detect and lint PSR-2 coding errors, but also do some minimal automatic
code style migration.

 - Install the necessary library:
   `composer require squizlabs/php_codesniffer`
 - Copy silverstripe standards config file from framework/phpcs.xml to your project root:
   `cp ./framework/phpcs.xml ./phpcs.xml`
 - Run the automatic upgrade tool on your code folder
   `vendor/bin/phpcbf ./mysite/code`
 - Run the automatic linting tool to detect and manually fix other errors:
   `vendor/bin/phpcs ./mysite/code`

Repeat the final step and manually repair suggested changes, as necessary,
until you no longer have any linting issues.

#### Upgrade user-code to use PSR-4 autoloading

While not critical to an upgrade, SilverStripe 4.0 has adopted the [PS-4 autoloading](http://www.php-fig.org/psr/psr-4/)
standard for the core modules, so it's probably a good idea to be consistent. 

You can implement this in your composer configuration like so:

```json
{
    "autoload": {
        "psr-4": {
            "WebDesignGroup\\ShopSite\\": "mysite/src/"
        }
    }
}
```

Now you just need to ensure that each class site in the correct folder location 
(including case sensitivity) to match its namespace. For example,
 `WebDesignGroup\ShopSite\Model\GalleryItem.php` should live at `mysite/src/Model/GalleryItem.php`.

Note that you don’t have to use `src/` as the root folder name. You can continue 
to use `code/` if you want to. SilverStripe has adopted the PSR-4 approach and 
have also started to use `src/` as a default folder location instead of 
`code/`. If you’re going to change, it's probably a good time to do it while you're
upgrading.

For examples, take a look at the file/folder structure and to the 
`composer.json` configuration in either the `framework` or `cms` modules.

Please note that there are changes to template structure which in some cases 
require templates to be in a folder location that matches the namespace of the class 
that it belongs to, e.g. `themes/mytheme/templates/MyVendor/Foobar/Model/MyModel.ss`.

## <a name="api-changes"></a>API Changes

### <a name="overview-general"></a>General and Core API

#### <a name="overview-general-api"></a>General and Core API Additions / Changes

* Minimum PHP version raised to 5.6 (with support for PHP 7.x)
* Dropped support for PHP safe mode (removed php 5.4).
* Once PHP versions become [unsupported by the PHP Project](http://php.net/supported-versions.php)),
  we drop support for those versions in the [next minor release](/contributing/release-process 
  This means PHP 5.6 and PHP 7.0 support will become unsupported in Dec 2018.
* Minimum CMS browser requirement raised from Internet Explorer 8 to Internet Explorer 11
* Updated PHPUnit from 3.7 to 4.8 ([upgrade notes](https://github.com/sebastianbergmann/phpunit/wiki/Release-Announcement-for-PHPUnit-4.0.0#backwards-compatibility-issues)).
  Please remove any PHPUnit related `require_once()` calls (e.g. in `FeatureContext`
  definitions of the [behat-extension](https://github.com/silverstripe-labs/silverstripe-behat-extension) module).
  Run `composer require --dev 'phpunit/phpunit:~4.8'` on existing projects to pull in the new dependency.
* `always_populate_raw_post_data` will now raise a deprecation warning in install.php when running in php 5.x,
  unless set to `-1`. This is due to `$HTTP_RAW_POST_DATA` being removed in php 7.
  See the [http://php.net/manual/en/reserved.variables.httprawpostdata.php](php documentation) for more information.
* Admin URL can now be configured via custom Director routing rule
* `Controller::init` visibility changed to protected. Use `Controller::doInit()` instead.
* `Controller::join_links` supports an array of link sections.
* `Object::useCustomClass` has been removed. You should use the config API with Injector instead.
* `Object::invokeWithExtensions` now has the same method signature as `Object::extend` and behaves the same way.
* `ServiceConfigurationLocator` is now an interface not a class.
* `i18nTextCollectorTask` merge is now true by default.
* `Object` has been broken up into various traits, each of which can be added to other objects independently:
  * `Configurable` Provides Config API helper methods
  * `Injectable` Provides Injector API helper methods
  * `Extensible` Allows extensions to be applied
* `Convert` class has extra methods for formatting file sizes in php_ini compatible format
  * `Convert::memstring2bytes()` will parse a php_ini memory size.
  * `Convert::bytes2memstring()` will format the memory size with the appropriate scale.
* `SiteTree.alternatePreviewLink` is deprecated. Use `updatePreviewLink` instead.
* `Injector` dependencies no longer automatically inherit from parent classes.
* `$action` parameter to `Controller::Link()` method is standardised.
* Moved test database cleanup task from `sake dev/tests/cleanupdb` to `sake dev/tasks/CleanupTestDatabasesTask`
* `Injector::load` given a `src` parameter will no longer guess the
  service name from the filename. Now the service name will either
  by the array key, or the `class` parameter value.
* Uniqueness checks for `File.Name` is performed on write only (not in `setName()`)
* Created `Resettable` interface to better declare objects which should be reset between tests.
* Added a server requirement for the php-intl extension (shipped by default with most PHP distributions)
* Replaced Zend_Date and Zend_Locale with the php-intl extension.
* Consistently use CLDR date formats (rather than a mix of CLDR and date() formats)
* Moved config into a new module: [silverstripe/config](https://github.com/silverstripe/silverstripe-config/).
  See upgrading notes below.
* Falsey config values (null, 0, false, etc) can now replace non-falsey values.
* Introduced new ModuleLoader manifest, which allows modules to be found via composer name.
 E.g. `$cms = ModuleLoader::inst()->getManifest()->getModule('silverstripe/cms')`
* `ClassManifest::getOwnerModule()` now returns a `Module` object instance.
* `Object` class has been removed.
  * `parse_class_spec` moved to `ClassInfo`
  * `create_from_spec` functionality removed, but now supportede by `Injector` natively.
  * `Injectable`, `Extensible` and `Configurable` traits added to support other methods.
* Certain methods have been moved from `Controller` to `RequestHandler`:
  * `Link`
  * `redirect`
  * `redirectBack`
* `RequestHandler` link and redirection behaviour has been enhanced slightly:
  * `Link` now relies on the `url_segment` handler being provided for the class.
    If left unset, this will raise an error.
  * `getBackURL` and `getReturnReferer` have been added to safely inspect the current request
    to see if there is a url to redirect back to.
* `LeftAndMain` class has had all tree manipulation code moved into CMS module class `CMSMain`.
  This includes:
  * `LeftAndMain_TreeNode` class -> renamed to `CMSMain_TreeNode`
  * `SiteTreeAsUL` removed (override left in `CMSMain`)
  * `getSiteTreeFor()` -> moved to `CMSMain`
  * `getsubtree()` -> moved to `CMSMain`
  * `updatetreenodes()` -> moved to `CMSMain`
  * `savetreenodes()` -> moved to `CMSMain`
  * `EditorToolbar()` method renamed to `Modals()` and now returns a `ModalController` handler
    instance rather than a `HTMLEditorField_Toolbar`
* Some `Director` API have been removed.
  * $dev_servers
  * $test_servers
  * $urlParams and setUrlParams()
  * `Director.alternate_host` removed. Use `Director.alternate_base_url` instead.
  * `Director.alternate_protocol` removed. Use `Director.alternate_base_url` instead.
* Global enviromnent variables changed:
  * 'BlockUntrustedIPS' env setting has been removed.
    All IPs are untrusted unless `SS_TRUSTED_PROXY_IPS` is set to '*'
    See [Environment Management docs](/getting-started/environment_management/) for full details.
  * `SS_TRUSTED_PROXY_HOST_HEADER`, `SS_TRUSTED_PROXY_PROTOCOL_HEADER`, and `SS_TRUSTED_PROXY_IP_HEADER`
    are no longer supported. These settings should go into the Injector service configuration for
    TrustedProxyMiddleware instead.
  * `MODULES_PATH` removed
  * `MODULES_DIR` removed
  * `SS_HOST` removed. Use `SS_BASE_URL` instead.
  * `Member::canLogIn()` now returns boolean. Use `Member::validateCanLogin()` to get a `ValidationResult`
* `Security` methods deprecated:
  * `has_default_admin` use `DefaultAdminService::hasDefaultAdmin()` instead
  * `check_default_admin` use `DefaultAdminService::isDefaultAdminCredentials()` instead
  * `default_admin_username` use `DefaultAdminService::getDefaultAdminUsername()` instead
  * `default_admin_password` use `DefaultAdminService::getDefaultAdminPassword()` instead
  * `setDefaultAdmin` use `DefaultAdminService::setDefaultAdmin()` instead
  * `clearDefaultAdmin` use `DefaultAdminService::clearDefaultAdmin()` instead
  * `findAnAdministrator` use `DefaultAdminService::findOrCreateDefaultAdmin()` instead
* `Member` methods deprecated:
  * `checkPassword`. Use Authenticator::checkPassword() instead
* `RequestFilter` has been deprecated in favour of
  [HTTPMiddleware](/developer_guides/controllers/middlewares). Also the legacy RequestFilter
  API has changed: $session and $dataModel variables removed from preRequest / postRequest.

#### <a name="overview-general-removed"></a>General and Core Removed API

* Removed `ConfigureFromEnv.php` as it's no longer necessary.
* `Session` object has had significant refactoring. This object no longer is accessed via
  `Session::inst()`, but instead should be queried from the current request via `$request->getSession()`.
  All static methods have been removed, and the `inst_` prefix removed from all instance members.
  Please see the upgrading section on Session object for more details.
* `Director.rules` config no longer support `redirect:<url>` directly via config.
* `Director::get_environment_type()` and `Director::set_environment_type()` are removed.
  Get the `Kernel` instance via injector and query `getEnvironment()` instead.
  E.g. `$type = Injector::inst()->get(Kernel::class)->getEnvironment();`.
* Many global methods have been refactored into `Environment` or `Convert` class.
  * `increase_xdebug_nesting_level_to` removed (functionality has been inlined into `AppKernel`)
  * `set_increase_time_limit_max` moved to `Environment::setTimeLimitMax()`
  * `get_increase_time_limit_max` moved to `Environment::getTimeLimitMax()`
  * `set_increase_memory_limit_max` moved to `Environment::setMemoryLimitMax()`
  * `get_increase_memory_limit_max` moved to `Environment::getMemoryLimitMax()`
  * `increase_time_limit_to` moved to `Environment::increaseTimeLimitTo()`
  * `increase_memory_limit_to` moved to `Environment::increaseMemoryLimitTo()`
  * `translate_memstring` moved to `Convert::memstring2bytes`.
  * `getTempFolder` moved to `TempFolder::getTempFolder()`
  * `getTempParentFolder` removed.
  * `getTempFolderUsername` removed.
* `CMSMain::buildbrokenlinks()` action is removed.
* `Injector::unregisterAllObjects()` has been removed. Use `unregisterObjects` to unregister
  groups of objects limited by type instead.
* `SS_Log` class has been removed. Use `Injector::inst()->get(LoggerInterface::class)` instead.
* Removed `CMSBatchAction_Delete`
* Removed `CMSBatchAction_DeleteFromLive`
* Removed `CMSMain.enabled_legacy_actions` config.
* `CMSmain.getCMSTreeTitle` is now ignored on extensions. Use `updateCMSTreeTitle` in extensions instead.
* Removed ability to run tests via web requests (`http://mydomain.com/dev/tests`), use the standard CLI
  command instead (`vendor/bin/phpunit`).
* Removed `dev/jstests/` controller (no replacement)
* Removed `TestRunner` and `JSTestRunner` APIs
* Removed `PhpUnitWrapper`, `PhpUnitWrapper_3_4`, `PhpUnitWrapper_3_5`, `PhpUnitWrapper_Generic`, `SapphireTestSuite` APIs
* Removed `SapphireTestReporter` and `CliTestReporter`
* Removed `SapphireTest::skipTest()`, use `markTestSkipped()` in a `setUp()` method instead
* Removed the `History.js` javascript library.
* `debugmethods` querystring argument has been removed from debugging.
* Moved `ErrorPage` into a new module: [silverstripe/errorpage](http://addons.silverstripe.org/add-ons/silverstripe/errorpage). See upgrading notes in that module.
* Removed `VirtualPage_Controller`. Virtual pages will now share whichever controller the “target” page uses
* Removed `Config_LRU`
* Removed `SilverStripeInjectionCreator`
* Removed `i18n::get_translatable_modules` method.
* Removed `i18nTextCollector_Writer_Php`
* `i18nTextCollector` no longer collects from `themes/<theme>` root dir.
  Modules which provide themes via `<moduleName>/themes/<theme>` are now preferred.
* Removed `i18nSSLegacyAdapter`
* Removed `FunctionalTest::stat`
* Removed `LeftAndMainMarkingFilter`
* Removed `Controller::getFormOwner`
* Removed `TeamCityListener`
* The Spyc YAML library has been removed from /thirdparty. Please load it yourself, or use the
  Symfony YAML component that’s automatically installed by composer.
* `RestfulService` has been removed. Use Guzzle instead. See Upgrading notes.
* Our self-maintained `Oembed` implementation has been removed, in favour of introducing
  [oscarotero/Embed](https://github.com/oscarotero/Embed) as a dependency.
* Removed TextParser and BBCodeParser. These are available in an archived module,
  [silverstripe-archive/bbcodeparser](https://github.com/silverstripe-archive/silverstripe-bbcodeparser)
* Removed `ViewableData::ThemeDir`. Use `ThemeResourceLoader::findThemedResource` in conjunction with `SSViewer::get_themes` instead.
* Removed `Config::FIRST_SET` and `Config::INHERITED`
* Removed `RequestHandler.require_allowed_actions`. This is now fixed to on and cannot be 
  disabled.
* Config or module searching methods have been removed from `ClassManifest`. Use `ModuleLoader`
  to get this information instead:
  - `getModules`
  - `getConfigDirs`
  - `getConfigs`
* Removed `Session::set_config()` and `Session::get_config()`. Use the `Session.timeout` config setting instead
* Removed `Security::set_login_recording()` and `Security::get_login_recording()`.
  Use the `Security.login_recording` config setting instead.
* Removed `ModelAsController::find_old_page()`. Use `OldPageRedirector::find_old_page()` instead
* Removed `RootURLController:set_default_homepage_link()` and `RootURLController::get_default_homepage_link()`.
  Use the `RootURLController.default_homepage_link` config setting instead.
* Removed `CreditCardField`, `CountryDropdownField`, `PhoneNumberField`, `MemberDatetimeOptionsetField`, `InlineFormAction`.
  Use custom code instead
* Removed `ResetFormAction`, use `FormAction::create()->setAttribute('type', 'reset')` instead
* `Injector` now complies with [PSR-11](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-11-container.md).
  Accordingly, `hasService()` has been renamed to `has()`, and `get()` will throw
  `SilverStripe\Core\Injector\InjectorNotFoundException` when the service can't be found.
* Removed `CustomMethods::createMethod()`. Use closures instead.

#### <a name="overview-general-deprecated"></a>General and Core Deprecated API

A very small number of methods were chosen for deprecation, and will be removed in 5.0 rather than 4.0

* `ClassInfo::baseDataClass` - Use `DataObject::getSchema()->baseDataClass()` instead.
* `ClassInfo::table_for_object_field` - Use `DataObject::getSchema()->tableForField()` instead
* `Config::inst()->update()` is deprecated. Use `Config::modify()->set()` or `Config::modify()->merge()`
  instead.

### <a name="overview-orm"></a>ORM API

#### <a name="overview-orm-api"></a>ORM API Additions / Changes

* Deprecate `SQLQuery` in favour `SQLSelect`
* `DataObject.many_many` 'through' relationships now support join dataobjects in place of
  automatically generated join tables. See the [/developer_guides/relations](datamodel relationship docs)
  for more info.
* `DataList::filter` by null now internally generates "IS NULL" or "IS NOT NULL" conditions
  appropriately on queries.
* `DataList::createDataObject` is now public.
* `DataObject` constructor now has an additional parameter, which must be included in subclasses.
* `DataObject::db` now returns composite fields.
* `DataObject::ClassName` field has been refactored into a `DBClassName` type field.
* `DataObject::can` has new method signature with `$context` parameter.
* `DataObject::duplicate` Now requires explicit flag to duplicate belongs_many_many (off by default),
  but now works with unsaved relations. By default only many_many are duplicated.
* `DBHTMLText` no longer enables shortcodes by default. Two injector aliases have been created for this
  class which can be used to select the correct behaviour:
  * `HTMLText`: `DBHTMLText` with shortcodes enabled
  * `HTMLFragment`: `DBHTMLText` without shortcodes enabled (as default)
* `CMSPreviewable` has been moved from the `SilverStripe\Admin` namespace to `SilverStripe\ORM`
* Changes to `DBString` formatting:
  * `NoHTML` is renamed to `Plain`
  * `LimitWordCountXML` is removed. Use `LimitWordCount` instead.
  * `BigSummary` is removed. Use `Summary` instead.
  * Most limit methods on `DBHTMLText` now plain text rather than attempt to manipulate the underlying HTML.
* `FormField::Title` and `FormField::RightTitle` are now cast as plain text by default (but can be overridden).
* `FormField#createTag()` has been renamed to `FormField::create_tag()`  
* `Hierarchy` class has had much of it's functionality refactored out into `MarkedSet`:
  * `isMarked`
  * `isTreeOpened`
  * `isExpanded`
  * `markByID`
  * `markPartialTree`
  * `markExpanded`
  * `markUnexpanded`
  * `markToExpose`
  * `markClosed`
  * `markOpened`
  * `markedNodeIDs`
  * `getChildrenAsUL` replaced with `renderChildren`, which now takes a template name.
  * `markingFilterMatches` (and made protected)
  * `markChildren` (and made protected)
* Removed `DataList::applyFilterContext` private method
* Search filter classes (e.g. `ExactMatchFilter`) are now registered with `Injector`
  via a new `DataListFilter.` prefix convention.
  see [search filter documentation](/developer_guides/model/searchfilters) for more information.
* `Permission::flush_permission_cache()` renamed to `reset()` and added to `Resettable` interface.
* `Versioned` API has some breaking changes:
  * Versioned constructor now only allows a single string to declare whether staging is enabled or not. The
    number of names of stages are no longer able to be specified. See below for upgrading notes for models
    with custom stages.
  * `reading_stage` is now `set_stage` and throws an error if setting an invalid stage.
  * `current_stage` is now `get_stage`
  * `getVersionedStages` is gone.
  * `get_live_stage` is removed. Use the `Versioned::LIVE` constant instead.
  * `getDefaultStage` is removed. Use the `Versioned::DRAFT` constant instead.
  * `$versionableExtensions` is now `private static` instead of `protected static`
  * `hasStages` is addded to check if an object has a given stage.
  * `stageTable` is added to get the table for a given class and stage.
  * Any extension declared via `versionableExtensions` config on Versioned dataobject must now
    `VersionableExtension` interface at a minimum. `Translatable` has been removed from default
    `versionableExtensions`
  * The default CMS delete behaviour for versioned dataobjects is now to delete from both draft
    and live stages, and to save to the archive. There is no longer a separate "Archive" action.
  * Any writes to versioned dataobjects (in either Draft or Live) will always write to the draft
    (main) table as a source of truth. This means that records created in Live mode will always be
    available to the CMS and in draft mode.
  * `_versions` suffixed tables are now renamed to `_Versions`. This fix will be automatically
    applied during dev/build.
* A lot of standard versioned API has been refactored from `SiteTree` into `Versioned` extension.
  * All versioned DataObjects have `canPublish()`, `canArchive()`, `canUnpublish()` permission checks
  * All versioned Dataobjects have `doPublish()`, `doArchive()`, `doPublish()`, and `doUnpublish()` actions.
    However, `do*()` methods will no longer automatically check `can*()` permissions, and must be done by
    usercode before invocation.
  * `SiteTree::getIsAddedToStage()` moved to `Versioned` and renamed to `isOnDraftOnly()`
  * `SiteTre::getIsModifiedOnStage()` moved to `Versioned` and renamed to `isModifiedOnDraft()`
  * `SiteTree::isPublished()` moved to `Versioned`.
  * `SiteTree::getExistsOnLive()` removed in favour of `isPublished()`
  * `isOnDraft()` added to `Versioned`.
  * `isArchived()` added to `Versioned`.
  * `isOnLiveOnly()` added to `Versioned`.
* `ChangeSet` and `ChangeSetItem` have been added for batch publishing of versioned dataobjects.
* `DataObject.table_name` config can now be used to customise the database table for any record.
* `DataObjectSchema` class added to assist with mapping between classes and tables.
* `DBMoney` values are now treated as empty only if `Amount` field is null. If an `Amount` value
  is provided without a `Currency` specified, it will be formatted as per the current locale.
* Removed `DatabaseAdmin#clearAllData()`. Use `DB::get_conn()->clearAllData()` instead
* `SapphireTest` temp DB methods have been removed and put into a new `TempDatabase` class.
  This allows applications to create temp databases when not running tests.
  This class now takes a connection name as a constructor class, and no longer
  has static methods.
  The following methods have been moved to this new class and renamed as non-static:
  * `using_temp_db` -> `isUsed()`
  * `kill_temp_db` -> `kill()`
  * `empty_temp_db` _> `clearAllData()`
  * `create_temp_db` -> `build()`
  * `delete_all_temp_dbs` -> `deleteAll()`
  * `resetDBSchema` -> `resetSchema()`

The below methods have been added or had their functionality updated to `DBDate`, `DBTime` and `DBDatetime`
* `getTimestamp()` added to get the respective date / time as unix timestamp (seconds since 1970-01-01)
* `Format()` method now use [CLDR format strings](http://userguide.icu-project.org/formatparse/datetime),
  rather than [PHP format string](http://php.net/manual/en/function.date.php).
  E.g. `d/m/Y H:i:s` (php format) should be replaced with to `dd/MM/y HH:mm:ss` (CLDR format).
* getISOFormat() added which returns the standard date/time ISO 8601 pattern in CLDR format.
* `setValue` method is now a lot more restrictive, and expects dates and times to be passed in
  ISO 8601 format (y-MM-dd) or (HH:mm:ss). Certain date formats will attempt to parse with
  the below restrictions:
  - `/`, `.` or `-` are supported date separators, but will be replaced with `-` internally.
  - US date formats (m-d-y / y-d-m) will not be supported and may be parsed incorrectly.
    (Note: Date form fields will still support localised date formats).
  - `dd-MM-y` will be converted to `y-MM-dd` internally.  
  - 2-digit values for year will now raise errors.
* `FormatFromSettings` will default to `Nice()` format if no member is logged in.
* `Nice`, `Long` and `Full` methods will now follow standard formatting rules for the
  current locale, rather than pre-defined formats.
* `Short` added to format concise date/time values, as a shorter version than `Nice`
* `getFormatter` method added, which returns a locale-specific date/time formatter.

`DBTime` specific changes:

* Added `DBTime::FormatFromSettings`

#### <a name="overview-orm-removed"></a>ORM Removed API

* Deprecated globals `$database` and `$databaseConfig`. Please use `DB::setConfig()` instead.
* `DataModel` removed
* `DataObject::can*` methods no longer accept a member ID. These must now be passed a Member object or left null
* `DataObject::db` removed and replaced with `DataObjectSchema::fieldSpec` and `DataObjectSchema::fieldSpecs`
* `DataObject::manyManyComponent` moved to `DataObjectSchema`
* `DataObject::belongsToComponent` moved to `DataObjectSchema`
* `DataObject::hasOneComponent` moved to `DataObjectSchema`
* `DataObject::hasManyComponent` moved to `DataObjectSchema`
* `DataObject::getRemoteJoinField` moved to `DataObjectSchema`
* `DataObject::database_fields` renamed and moved to `DataObjectSchema::databaseFields`
* `DataObject::has_own_table` renamed and moved to `DataObjectSchema::classHasTable`
* `DataObject::composite_fields` renamed and moved to `DataObjectSchema::compositeFields``
* `DataObject::manyManyExtraFieldsForComponent` moved to `DataObjectSchema`
* Removed `DataObject::validateModelDefinitions`. Relations are now validated within `DataObjectSchema`
* Removed `DataObject` methods `hasOwnTableDatabaseField`, `has_own_table_database_field` and
  `hasDatabaseFields` are superceded by `DataObjectSchema::fieldSpec`.
  Use `$schema->fieldSpec($class, $field, DataObjectSchema::DB_ONLY | DataObjectSchema::UNINHERITED )`.
  Exclude `uninherited` option to search all tables in the class hierarchy.
* Removed `DataObject::is_composite_field`. Use `DataObjectSchema::compositeField` instead.
* Removed `DataObject::custom_database_fields`. Use `DataObjectSchema::databaseFields`
  or `DataObjectSchema::fieldSpecs` instead.
* Removed `DataList::getRelation`, as it was mutable. Use `DataList::applyRelation` instead, which is immutable.
* Removed `DataList::applyFilterContext` private method
* `Member` Field 'RememberLoginToken' removed, replaced with 'RememberLoginHashes' has_many relationship
* Removed `UpgradeSiteTreePermissionSchemaTask`
* Removed `EncryptAllPasswordsTask`
* Removed `DBString::LimitWordCountXML()` method. Use `LimitWordCount` for XML safe version.
* Removed `SiteTree::getExistsOnLive()`. Use `isPublished()` instead.
* Removed `SiteTree::getIsDeletedFromStage()`. Use `isOnDraft()` instead (inverse case).
* `DataObject.many_many` no longer supports triangular resolution. Both the `many_many` and `belongs_many_many`
  must point directly to the specific class on the opposing side, not a subclass or parent.
* `DataObject::validateModelDefinitions()` has been removed. Validation and parsing of config is now handled
  within `DataObjectSchema`.
* `CMSBatchAction_Delete` removed. Use `CMSBatchAction_Archive` instead.
* Removed several DBDate methods:
  - `past_date`
  - `prior_monday`
  - `weekday`
  - `next_day`
  - `day_before`
  - `days_between`
* `nice_format` has been removed from `DBDate` / `DBTime` / `DBDatetime` has been removed in favour of
  locale-specific formatting for Nice()
* Removed several `DBTime` methods:
  - `TwelveHour`
  - `Nice24`
* Removed some `DBMoney` methods due to lack of support in php-intl.
  - `NiceWithShortname`
  - `NiceWithName`
  - `getShortName`
  - `getCurrencyName`
* Removed additional arguments from `DBMoney::getSymbol`. The result of this value is
  now localised based on the currency code assigned to the `DBMoney` instance
* Removed `DBMoney::getAllowedCurrencies`. Apply validation to `MoneyField` instead.
* `Hierarchy` has lots of removed api:
  - `parentStack()` removed. Use `getAncestors()` instead
  - `doAllChildrenIncludingDeleted()` removed. Use `AllChildrenIncludingDeleted()` instead.
  - `naturalNext` removed.
  - `naturalPrev` removed.
  - `markingFinished` removed.

### <a name="overview-filesystem"></a>Filesystem API

#### <a name="overview-filesystem-api"></a>Filesystem API Additions / Changes

* Image manipulations have been moved into a new `[ImageManipulation](api:SilverStripe\Assets\ImageManipulation)` trait.
* `CMSFileAddController` removed.
* `UploadField::setAllowedFileCategories('image')` now excludes non-resizeable images. 'unresizeable_image' is
  can be used to validate these types.
* `Image_Backend` API now loads and saves from `AssetContainer` instances rather than local files.
* The following File categories have been renamed: 'zip' to 'archive', 'doc' to 'document', and 'mov' to 'video'
* `File::updateLinks` no longer takes urls as parameters. All file links are now identified either by
  the `DataObject::ID` in a `data-fileid` property, or via shortcodes. This is necessary because file
  urls are no longer able to identify assets.
* Extension point `HtmlEditorField::processImage` has been removed, and moved to `Image::regenerateImageHTML`
* `Upload::load` now stores assets directly without saving into a `File` dataobject.
* Protected file storage is now a core Framework API. See [/developer_guides/files/file_security] for
  more information.
* `File` is now versioned, and should be published before they can be used on the frontend.
  See section on [Migrating File DataObject from 3.x to 4.0](#migrating-file-dataobject-from-3x-to-40)
  below for upgrade notes.
* New filesystem abstraction including new `DBFile` database field to hold file references.
* `ShortcodeHandler` interface to help generate standard handlers for HTML shortcodes in the editor.
* `handle_shortcode` methods are removed from `File` and `Image` and moved to their own classes in `SilverStripe\Assets\Shortcodes` and are named `FileShortcodeProvider` and `ImageShortcodeProvider` respectively.
* `AssetNameGenerator` interface, including a `DefaultAssetNameGenerator` implementation, which is used to generate
  renaming suggestions based on an original given filename in order to resolve file duplication issues.
* `GeneratedAssetHandler` API now used to store and manage generated files (such as those used for error page
  cache or combined files).
* `Requirements_Minifier` API can be used to declare any new mechanism for minifying combined required files.
  By default this api is provided by the `JSMinifier` class, but user code can substitute their own.
* `AssetField` formfield to provide an `UploadField` style uploader for the new `DBFile` database field.
* `AssetControlExtension` is applied by default to all DataObjects, in order to support the management
  of linked assets and file protection.
* `ProtectedFileController` class is used to serve up protected assets.

#### <a name="overview-filesystem-removed"></a>Filesystem removed API

The following image manipulations previously deprecated has been removed:

* `Image::SetRatioSize` superceded by `Fit`
* `Image::SetWidth` superceded by `ScaleWidth`
* `Image::SetHeight` superceded by `ScaleHeight`
* `Image::SetSize` superceded by `Pad`
* `Image::PaddedImage` superceded by `Pad`
* `Image::CroppedImage` superceded by `Fill`
* `Image::AssetLibraryPreview` superceded by `PreviewThumbnail`
* `Image::AssetLibraryThumbnail` superceded by `CMSThumbnail`

The following `File` methods have been removed. Since there is no longer any assumed local path for any file,
methods which dealt with such paths may no longer be relied on.

* `File::deletedatabaseOnly`
* `File::link_shortcode_handler` renamed to `handle_shortcode`
* `File::setParentID`
* `File::getFullPath`
* `File::getRelativePath`
* `File::Content` database field is removed

Image manipulations have been moved out of Image.php and now available to any File or DBFile which has the
appropriate mime types. The following file manipulations classes and methods have been removed:

* `Image_Cached` class
* `Image::regenerateFormattedImages` method
* `Image::getGeneratedImages` method
* `Image::deleteFormattedImages` method
* `Image::handle_shortcode` moved to `SilverStripe\Assets\Shortcodes\ImageShortcodeProvider::handle_shortcode`
* `AssetAdmin::deleteunusedthumbnails` method
* `AssetAdmin::getUnusedThumbnails` method

Many `Folder` api have also been removed:

* `Folder_UnusedAssetsField` class
* `Folder::syncChildren` method
* `Folder::constructChild` method
* `Folder::addUploadToFolder` method

The following filesystem synchronisation methods and tasks are also removed

* `RegenerateCachedImagesTask` class
* `CleanImageManipulationCache` class
* `Filesystem::sync` method
* `AssetAdmin::doSync` method

### <a name="overview-template"></a>Template and Form API

#### <a name="overview-template-api"></a>Template and Form API Additions / Changes

* Upgrade of TinyMCE to version 4.
* Templates now use a standard template lookup system via `SSViewer::get_templates_by_class`
  which builds a candidate list for a given class. Actual resolution of existing templates
  for any list of candidates is actually performed by `SSViewer::chooseTemplate`
* `HtmlEditorConfig` is now an abstract class, with a default implementation `TinyMCEConfig` for the built in
  TinyMCE editor.
* `HtmlEditorField::setEditorConfig` may now take an instance of a `HtmlEditorConfig` class, as well as a
  standard config identifier name.
* `HeaderField` requires a `$name` constructor argument (`new HeaderField('MyName', 'My Title')`
* `default_cast` is now enforced on all template variables. See upgrading notes below.
* FormField templates no longer look in the 'forms' folder for templates. As all form fields are
  now namespaced, the path for these templates will now match the namespace of the given class instead.
* `$module` parameter in `themedCSS` and `themedJavascript` removed.
* Theme selector has been removed from SiteConfig. Please use `SSViewer.themes` config instead.
* `FormAction::setValidationExempt` can be used to turn on or off form validation for individual actions
* GridField edit form now has improved support for versioned DataObjects, with basic publishing
  actions available when editing records.
* `PopoverField` added to provide popup-menu behaviour in react forms (currently not available for
  non-react forms).
* Introduction of experimental `FormFactory` API as a substitute for DataObject classes being responsible
  for building their own form fields. This builds a form based on a given controller and model,
  and can be customised on a case by case basis. This has been introduced initially for the asset-admin
  module.
* Introduced `AssetAdmin\Forms\UploadField` as a react-friendly version of UploadField. This may also
  be used in normal entwine forms for managing files in a similar way to UploadField. However, this
  does not support inline editing of files.
* Added method `FormField::setSubmittedValue($value, $data)` to process input submitted from form
  submission, in contrast to `FormField::setValue($value, $data)` which is intended to load its
  value from the ORM. The second argument to setValue() has been added.
* `HTMLValue` service name is now fully qualified `SilverStripe\View\Parsers\HTMLValue`.
* FormField::create_tag() has been moved to `HTML` class and renamed to createTag. Invoke with
  `HTML::createTag()`.

The following methods and properties on `Requirements_Backend` have been renamed:

* `Requirements_Backund::$combine_files` made protected and renamed `$combinedFiles`
* `Requirements_Backend::$combine_js_with_min` made protected and renamed `$minifyCombinedFiles`
* `Requirements_Backend::$write_header_comments` made protected and renamed `$writeHeaderComment`
* `Requirements_Backend::$write_js_to_body` made protected and renamed to `$writeJavascriptToBody`
* `Requirements_Backend::$force_js_to_bottom` renamed to `$forceJSToBottom`
* `get_combined_files_enabled` renamed to `getCombinedFilesEnabled`
* `set_combined_files_enabled` renamed to `setCombinedFilesEnabled`
* `get_suffix_requirements` renamed to `getSuffixRequirements`
* `set_suffix_requirements` renamed to `setSuffixRequirements`
* `get_custom_scripts` renamed to `getCustomScripts`
* `unblock_all` renamed to `unblockAll`
* `include_in_response` renamed to `includeInResponse`
* `combine_files` renamed to `combineFiles`
* `get_combine_files` renamed to `getCombinedFiles`
* `clear_combined_files` renamed to `clearCombinedFiles`
* `process_combined_files` renamed to `processCombinedFiles`
* `set_write_js_to_body` renamed to `setWriteJavascriptToBody`
* `set_force_js_to_bottom` renamed to `setForceJSToBottom`

New methods on `Requirements` are added to access these:

* `get_minify_combined_js_files`
* `set_minify_combined_js_files`
* `get_force_js_to_bottom`
* `get_write_js_to_body`

Some methods on `Requirements` have had their method signatures changed:

* `includeInHTML` has had the first parameter $template removed as it was previously deprecated.

A new config `Requirements_Backend.combine_in_dev` has been added in order to allow combined files to be
forced on during development. If this is off, combined files is only enabled in live environments.

Form validation has been refactored significantly. A new `FormMessage` trait has been created to
handle field-level and form-level messages. This has the following properties:

* `setMessage` to assign a message, type, and cast
* `getMessage` retrieves the message string
* `getMessageType` retrieves the message type (E.g. error, good, info)
* `getMessageCast` retrieves the cast type
* `getMessageCastingHelper` retrieves the DBField cast to use for the appropriate message cast
* `getSchemaMessage` encodes this message for form schema use in ReactJS.

`Form` behaviour methods have been changed:

* __construct() now allows a RequestHandler to be passed as a first argument, rather than a Controller.
  in addition this argument is now optional. This allows forms to be constructed as a model only.
* `validate` is replaced with `validationResult` instead, which returns a `ValidationResult` instance.
  This is no longer automatically persisted in the state by default, unless a redirection occurs.
  You can also save any response in the state by manually invoking `saveFormState` inside a custom
  validation response handler.
* `setupFormErrors` renamed to `restoreFormState`
* `resetValidation` renamed to `clearFormState`
* `loadMessagesFrom` method created to load a ValidationResult into a form.
* `setMessage`. third parameter is now $cast type
* `messageForForm` removed. Use `setMessage` or `sessionMessage` instead.
* `getSessionValidationResult` / `setSessionValidationResult` used to get / set session errors
* `getSessionData` / `setSessionData` used to get / set field values cached in the session
* `getAjaxErrorResponse` and `getRedirectReferer` created to simplify `getValidationErrorResponse`
* `addErrorMessage` removed. Users can either use `sessionMessage` or `sessionError` to add a
  form level message, throw a ValidationException during submission, or add a custom validator.
* `Form` is no longer a `RequestHandler`, but implements the `HasRequestHandler` interface and returns
  a `FormRequestHandler` instance from `getRequestHandler()`. the `Form` constructor no longer has
  any mandatory parameters, and the first parameter allows a non-`Controller` `RequestHandler` to be
  passed. Certain methods have been moved from `Form` to `FormRequestHandler`:
  * `buttonClicked`
  * `checkAccessAction`
  * `handleField`
  * `httpSubmission`
  * `Link`

`Validator` methods have changed:

* `validate` method now returns a `ValidationResult` instance.
* `requireField` method removed. Use `RequiredFields` subclass instead.

`ValidationResult` now has these methods:

* `serialize` / `unserialize` for saving within session state
* `messageList` renamed to `getMessages`
* `error` method replaced with `addMessage` / `addError` / `addFieldMessage` / `addFieldError`
* `valid` renamed to `isValid`

`ValidationException` has these changes:

* `$message` second constructor parameter is removed. Constructor only accepts `$result`,
  which may be a string, and optional `$code`
  
New `DatetimeField` methods replace `getConfig()` / `setConfig()`:

* `getTimezone()` / `setTimezone()`
* `getDateTimeOrder()` / `setDateTimeOrder()`
* `getLocale()` / `setLocale()`
* `datavaluefield` config is removed as internal data value is now fixed to ISO 8601 format

The `DatetimeField` has changed behaviour:

* It uses a combined input instead of a composite from `DateField` and `TimeField`
  Consequently, `getDateField()` and `getTimeField()` have been removed.
* It returns [ISO 8601 normalised dates](https://html.spec.whatwg.org/multipage/infrastructure.html#local-dates-and-times)
  by default in `Value()`, which include a "T" separator between date and time. 
  This is required to allow HTML5 input. Either use `setHTML5(false)` to set your custom format,
  or use `dataValue()` to retrieve a whitespace separated representation. 
* It no longer accepts `setValue()` as an array with 'date' and 'time' keys
* Added `getHTML5()` / `setHTML5()`

New `DateField` methods replace `getConfig()` / `setConfig()`:

* `getDateFormat()` / `setDateFormat()`
* `getMinDate()` / `setMinDate()`
* `getMaxDate()` / `setMaxDate()`
* `getLocale()` / `setLocale()`

The `DateField` has changed behavior:

* `DateField` no longer provides a jQuery UI date picker (`showcalendar` option),
   and uses [HTML5 date pickers](https://www.wufoo.com/html5/types/4-date.html) by default instead.
* `DateField` provides an optional polyfill for
  [browsers without HTML5 date picker support](http://caniuse.com/#feat=input-datetime) 
* The `dmyfields` option has been replced with native HTML5 behaviour (as one single `<input type=date>`).
* `getClientLocale` / `setClientLocale` have been removed (handled by `DateField->locale` and browser settings)

New `TimeField` methods replace `getConfig()` / `setConfig()`

* `getTimeFormat()` / `setTimeFormat()`
* `getLocale()` / `setLocale()`
* `getClientConfig()` has been removed (in favour of `setHTML5()`)

#### <a name="overview-template-removed"></a>Template and Form Removed API

* Removed `TabularStyle`
* Removed `NestedForm`
* Removed `FieldList` methods:
  * `getTabPathRewrites`
  * `setTabPathRewrites`
  * `rewriteTabPath`
* Removed `Form` methods (see above for replacements):
  * `transformTo`
  * `callfieldmethod`
  * `single_field_required`
  * `current_action`
  * `set_current_action`
  * `setupFormErrors`
  * `resetValidation`
  * `messageForForm`
  * `addErrorMessage`
  * `testSubmission`
  * `testAjaxSubmission`
* Removed `Validator::requireField()` method.
* Removed `ValidationResult` (see above for replacements):
  * `messageList`
  * `codeList`
  * `message`
  * `starredList`
  * `error`
  * `valid`
* Removed `ReportAdminForm.ss` template
* `FormField::dontEscape()` has been removed. Escaping is now managed on a class by class basis.
* Removed `PermissionCheckboxSetField::getAssignedPermissionCodes()` (never implemented)
* `Requirements::delete_combined_files()` and `Requirements::delete_combined_files()` methods have been removed
 as they are obsolete.
* Removed `DatetimeField`, `DateField` and `TimeField` methods `getConfig` and `setConfig`. Individual
  getters and setters for individual options are provided instead. See above for list of new methods.
* Removed `NumericField_Readonly`. Use `setReadonly(true)` instead.
* `SSViewer` deprecated methods removed:
  * `set_source_file_comments()`
  * `get_source_file_comments()`
  * `getOption`
  * `setOption`  
* Removed `MemberDatetimeOptionsetField` (no replacement)
* Removed `DateField_View_JQuery` (replaced with native HTML5 support in `DateField`)
* The following HTMLEditorField_* classes have been removed:
  * `HTMLEditorField_Toolbar` (replaced With `ModalController` in admin module)
  * `HTMLEditorField_Embed` (replaced with `EmbedResource` in asset-admin module)
  * `HTMLEditorField_File`
  * `HTMLEditorField_Flash`
  * `HTMLEditorField_Image`

### <a name="overview-i18n"></a>i18n API

#### <a name="overview-i18n-api"></a>i18n API Additions / Changes

* Upgrade of i18n to symfony/translation
* Localisation based on language-only (without any specific locale) is now supported
* `i18nEntityProvider::provideI18nEntities()` Now is expected to return only a single array
  map of key to default values.
* i18n keys for '.PLURAL_NAME' and '.SINGULAR_NAME' have been changed back to use the namespaced class names
  for all DataObject subclasses, rather than just the basename without namespace.
* i18n key for locale-respective pluralisation rules added as '.PLURALS'. These can be configured
  within yaml in array format as per [ruby i18n pluralization rules](http://guides.rubyonrails.org/i18n.html#pluralization).
* `i18n.all_locales` config moved to `SilverStripe\i18n\Data\Locales.locales`
* `i18n.common_languages` config moved to `SilverStripe\i18n\Data\Locales.languages`
* `i18n.likely_subtags` config moved to `SilverStripe\i18n\Data\Locales.likely_subtags`
* `i18n.tinymce_lang` config moved to `SilverStripe\Forms\HTMLEditor\TinyMCEConfig.tinymce_lang`
* `i18n::get_tinymce_lang()` moved to `SilverStripe\Forms\HTMLEditor\TinyMCEConfig::get_tinymce_lang()`
* `i18n::get_locale_from_lang()` moved to `SilverStripe\i18n\Data\Locales::localeFromLang()`
* `i18n::get_lange_from_locale()` moved to `SilverStripe\i18n\Data\Locales::langFromLocale()`
* `i18n::validate_locale()` moved to `SilverStripe\i18n\Data\Locales::validate()`
* `i18n::get_common_languages()` moved to `SilverStripe\i18n\Data\Locales::getLanguages()`
* `i18n::get_locale_name()` moved to `SilverStripe\i18n\Data\Locales::localeName()`
* `i18n::get_language_name()` moved to `SilverStripe\i18n\Data\Locales::languageName()`
* `i18n.module_priority` config moved to `SilverStripe\i18n\Data\Sources.module_priority`
* `i18n::get_owner_module()` moved to `SilverStripe\Core\Manifest\ClassManifest::getOwnerModule()`
  This now returns a `Module` object instance instead of a string.
* `i18n::get_existing_translations()` moved to `SilverStripe\i18n\Data\Sources::getKnownLocales()`

#### <a name="overview-i18n-removed"></a>i18n API Removed API

* `Zend_Translate` removed
* `i18n::_t()` Support for sprintf-style `%s` arguments deprecated
* `i18n::_t()` Using non-associative injection with named parameters is now an error
* `i18n::get_language_name()` removed.
* `i18n::get_language_code()` removed.
* `i18n::get_common_locales()` removed.
* `i18n.common_locales` config removed

#### <a name="overview-mailer"></a>Email Additions / Changes

* `Mailer` converted to an interface
* `SwfitMailer` added as new default mailer
* `Email` re-written to be powered by [SwiftMailer](https://github.com/swiftmailer/swiftmailer)
* Default template body variable renamed from `$Body` to `$EmailContent`
* `$email->setTemplate()` renamed to `$email->setHTMLTemplate()`
* Added `$email->setPlainTemplate` for rendering plain versions of email
* `$email->populateTemplate()` has been replaced with `$email->setData()`

### <a name="overview-testing"></a>SapphireTest

* `is_running_tests()` is no longer public and user code should not rely on this. Test-specific behaviour
  should be implemented in `setUp()` and `tearDown()`
* `setUpOnce` removed. Please use `setUpBeforeClass`
* `tearDownOnce` removed. Please use `tearDownAfterClass`
* `TestListener` class removed
* `SapphireTest::$requiredExtensions` renamed to `SapphireTest::$required_extensions` and made static
* `SapphireTest::$extraDataObjects` renamed to `SapphireTest::$extra_dataobjects` and made static
* `SapphireTest::$extraControllers` renamed to `SapphireTest::$extra_controllers` and made static

### <a name="overview-security"></a>Security

 * `LoginForm` now has an abstract method `getAuthenticatorName()`. If you have made subclasses of this,
   you will need to define this method and return a short name describing the login method.
 * `MemberLoginForm` has a new constructor argument for the authenticator class, athough tis is usually
   constructed by `MemberAuthenticator` and won't affect normal use.
 * `Authenticator` methods `register` and `unregister` are deprecated in favor of using `Config`