Add Matomo 4 Plugin Migration guide

docs/4.x/develop-migration.md

@@ -2,6 +2,7 @@
 category: Develop
 title: Migrations
 subGuides:
+  - migrate-matomo-3-to-4
   - migrate-piwik-2-to-3
 ---
 

docs/migrate-matomo-3-to-4.md

@@ -0,0 +1,79 @@
+---
+category: Develop
+---
+# Migrate Plugin from Matomo 3.X to Matomo 4
+
+This migration guide covers explains how to do some migrations to make a plugin compatible with Matomo 4. A list of
+all changes in Matomo 4 can be found in the [Changelog](/changelog).
+
+## Adjust the required Matomo version
+
+For your plugin to be executed in Matomo 4 you first need to show it is compatible with Matomo 4 in your `plugin.json` file:
+
+* specify that your plugin requires Matomo 4 (the require for Piwik 3 used to be eg `"piwik": ">=3.0.0-b1,<4.0.0-b1"`). 
+* we recommend to also increase your plugin's major version number eg from `3.2.3` to `4.0.0`.
+
+The `plugin.json` would look like this:
+
+```json
+   "version": "4.0.0",
+   "require": {
+        "matomo": ">=4.0.0-b1,<5.0.0-b1"
+    },
+```
+
+## Required PHP version
+
+We now require PHP 7.2.5 instead of PHP 5.5. This means you can use more PHP language features:
+
+* [New features in PHP 5.6](https://www.php.net/manual/en/migration56.new-features.php)
+* [New features in PHP 7.0](https://www.php.net/manual/en/migration70.new-features.php)
+* [New features in PHP 7.1](https://www.php.net/manual/en/migration71.new-features.php)
+* [New features in PHP 7.2](https://www.php.net/manual/en/migration72.new-features.php)
+
+## Browser support
+
+We no longer support IE 10 in the Matomo user interface.
+
+## Events
+
+If your plugin is listening to events you have to rename the method `getListHooksRegistered` to `registerEvents`.
+
+There are also various other event changes see the [changelog](/changelog).
+
+## Twig templates
+
+We updated from Twig 1 to Twig 3 which requires a few changes should you be using twig templates.
+
+You can find details on that on this deprecation lists.
+
+[Twig 2 changes](https://twig.symfony.com/doc/1.x/deprecated.html) | 
+[Twig 3 changes](https://twig.symfony.com/doc/2.x/deprecated.html)
+
+Changes from those lists we had to apply in core:
+
+* Adding an if condition on a for tag is deprecated in Twig 2.10. Use a filter filter or an “if” condition inside the “for” body instead (if your condition depends on a variable updated inside the loop).
+
+eg. 
+```
+{% for id,name in list if id > 17 %}
+```
+becomes
+```
+{% for id,name in list|filter(id=> id > 17) %}
+```
+
+* The spaceless tag is deprecated in Twig 2.7. Use the spaceless filter instead or {% apply spaceless %} (the Twig\Node\SpacelessNode and Twig\TokenParser\SpacelessTokenParser classes are also deprecated).
+
+e.g. `{% spaceless %}` becomes `{% apply spaceless %}`
+
+* The sameas and divisibleby tests are deprecated in favor of same as and divisible by respectively.
+
+e.g. `divisibleby(2)` becomes `divisible by(2)`
+
+## Summary
+
+In this guide we have seen which steps to take to migrate your Matomo plugin to be compatible with our latest Matomo 4.
+If you need further help for converting your plugin to Matomo 3, head over to the [Piwik developers community forums](https://forum.matomo.org/c/plugins-platform).
+
+Once you've adjusted your plugin, don't forget to release a new version.