plugin_extensions_and_extension_points.md

title
Plugin Extensions and Extension Points

The IntelliJ Platform provides the concept of extensions and extension points that allows a plugin to interact with other plugins or with the IDE itself.

Extension points

If you want your plugin to allow other plugins to extend its functionality, in the plugin, you must declare one or several extension points. Each extension point defines a class or an interface that is allowed to access this point.

Extensions

If you want your plugin to extend the functionality of other plugins or the IntelliJ Platform, you must declare one or several extensions.

How to declare extensions and extension points

You can declare extensions and extension points in the plugin configuration file plugin.xml, within the <extensions> and <extensionPoints> sections, respectively.

To declare an extension point

In the <extensionPoints> section, insert a child element <extensionPoint> that defines the extension point name and the name of a bean class or an interface that is allowed to extend the plugin functionality in the name, beanClass and interface attributes, respectively.

To clarify this procedure, consider the following sample section of the plugin.xml file:

<extensionPoints>
  <extensionPoint name="MyExtensionPoint1" beanClass="MyPlugin.MyBeanClass1">
  <extensionPoint name="MyExtensionPoint2" interface="MyPlugin.MyInterface">
</extensionPoints>

• The interface attribute sets an interface the plugin that contributes to the extension point must implement.
• The beanClass attribute sets a bean class that specifies one or several properties annotated with the @Attribute annotation.

The plugin that contributes to the extension point will read those properties from the plugin.xml file.

To clarify this, consider the following sample MyBeanClass1 bean class used in the above plugin.xml file:

public class MyBeanClass1 extends AbstractExtensionPointBean {
  @Attribute("key")
  public String key;

  @Attribute("implementationClass")
  public String implementationClass;

  public String getKey() {
    return key;
  }

  public String getClass() {
    return implementationClass;
  }
}

To declare an extension designed to access the MyExtensionPoint1 extension point, your plugin.xml file must contain the <MyExtensionPoint1> tag with the key and implementationClass attributes set to appropriate values (see sample below).

To declare an extension

TIP Auto-completion is available for all these steps.

1. For the <extensions> element, set the defaultExtensionNs attribute to one of the following values:
   • com.intellij, if your plugin extends the IntelliJ Platform core functionality.
   • {ID of a plugin}, if your plugin extends a functionality of another plugin.
2. Add a new child element to the <extensions> element. The child element name must match the name of the extension point you want the extension to access.
3. Depending on the type of the extension point, do one of the following:
   • If the extension point was declared using the interface attribute, for newly added child element, set the implementation attribute to the name of the class that implements the specified interface.
   • If the extension point was declared using the beanClass attribute, for newly added child element, set all attributes annotated with the @Attribute annotations in the specified bean class.

To clarify this procedure, consider the following sample section of the plugin.xml file that defines two extensions designed to access the appStarter and applicationConfigurable extension points in the IntelliJ Platform and one extension to access the MyExtensionPoint1 extension point in a test plugin:

<!-- Declare extensions to access extension points in the IntelliJ Platform.
     These extension points have been declared using the "interface" attribute.
 -->
  <extensions defaultExtensionNs="com.intellij">
    <appStarter implementation="MyTestPackage.MyTestExtension1" />
    <applicationConfigurable implementation="MyTestPackage.MyTestExtension2" />
  </extensions>

<!-- Declare extensions to access extension points in a custom plugin
     The MyExtensionPoint1 extension point has been declared using *beanClass* attribute.
-->
  <extensions defaultExtensionNs="MyPluginID">
     <MyExtensionPoint1 key="keyValue" implementationClass="MyTestPackage.MyClassImpl"></MyExtensionPoint1>
  </extensions>

Extension default properties

The following properties are available always:

• id - unique ID
• order - allows to order all defined extensions using first, last or before|after [id] respectively
• os - allows to restrict extension to given OS, e.g., os="windows" registers the extension on Windows only

Extension properties code insight

Several tooling features are available to help configuring bean class extension points in plugin.xml.

Property names matching the following list will resolve to FQN:

• implementation
• className
• serviceInterface / serviceImplementation
• ending with Class (case-sensitive)

A required parent type can be specified in the extension point declaration via nested <with>:

    <extensionPoint name="myExtension" beanClass="MyExtensionBean">
      <with attribute="psiElementClass" implements="com.intellij.psi.PsiElement"/>
    </extensionPoint>

Property name language will automatically resolve to all present Language IDs.

Specifying @org.jetbrains.annotations.Nls verifies capitalization of UI text properties according to given capitalization value (2019.2 and later).

How to get the extension points list?

To get a list of extension points available in the IntelliJ Platform core, consult the <extensionPoints> section of the following XML configuration files:

• LangExtensionPoints.xml
• PlatformExtensionPoints.xml
• VcsExtensionPoints.xml