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plugin_extensions.md

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Plugin Extensions
/basics/plugin_structure/plugin_extensions_and_extension_points.html

Extensions are the most common way for a plugin to extend the functionality of the IntelliJ Platform in a way that is not as straightforward as adding an action to a menu or toolbar. The following are some of the most common tasks accomplished using extensions:

  • The com.intellij.toolWindow extension point allows plugins to add tool windows (panels displayed at the sides of the IDE user interface);
  • The com.intellij.applicationConfigurable and com.intellij.projectConfigurable extension points allow plugins to add pages to the Settings/Preferences dialog;
  • Custom language plugins use many extension points to extend various language support features in the IDE.

There are more than 1000 extension points available in the platform and the bundled plugins, allowing to customize different parts of the IDE behavior.

Declaring Extensions

TIP Auto-completion, Quick Documentation and other code insight features are available on extension point tags and attributes.

  1. Add an <extensions> element to your plugin.xml if it's not yet present there. 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 com.intellij.appStarter and com.intellij.projectTemplatesFactory extension points in the IntelliJ Platform and one extension to access the another.plugin.myExtensionPoint extension point in another plugin another.plugin:

<!-- Declare extensions to access extension points in the IntelliJ Platform.
     These extension points have been declared using "interface".
 -->
  <extensions defaultExtensionNs="com.intellij">
    <appStarter implementation="com.myplugin.MyAppStarter" />
    <projectTemplatesFactory implementation="com.myplugin.MyProjectTemplatesFactory" />
  </extensions>

<!-- Declare extensions to access extension points in a custom plugin "another.plugin"
     The "myExtensionPoint" extension point has been declared using "beanClass" 
     and exposes custom properties "key" and "implementationClass".
-->
  <extensions defaultExtensionNs="another.plugin">
     <myExtensionPoint key="keyValue" implementationClass="com.myplugin.MyExtensionPointImpl" />
  </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.

Properties annotated with @RequiredElement are inserted automatically and validated (2019.3 and later).

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