intellij-sdk-code-samples/topics/tutorials/custom_language_support/annotator.md

An Annotator helps highlight and annotate any code based on specific rules. This section adds annotation functionality to support the Simple Language in the context of Java code.

Reference: Annotator

Required Project Configuration Changes

Classes defined in this step of the tutorial depend on com.intellij.psi.PsiLiteralExpression (the PSI representation for String literals in Java code) at runtime. Using PsiLiteralExpression introduces a dependency on com.intellij.java.

Beginning in version 2019.2, a dependency on Java plugin must be declared explicitly. First, add a dependency on the Java plugin in Gradle build file:

intellij {
  plugins = ['com.intellij.java']
}

intellij {
  plugins.set(listOf("com.intellij.java"))
}

Then, declare the dependency in plugin.xml (use code insight)

  <depends>com.intellij.java</depends>

Define an Annotator

The SimpleAnnotator subclasses Annotator. Consider a literal string that starts with "simple:" as a prefix of a Simple Language key. It isn't part of the Simple Language, but it is a useful convention for detecting Simple Language keys embedded as string literals in other languages, like Java. Annotate the simple:key literal expression, and differentiate between a well-formed vs. an unresolved property.

The use of new AnnotationHolder syntax starting 2020.2, which uses the builder format.

{type="note"}

{src="simple_language_plugin/src/main/java/org/intellij/sdk/language/SimpleAnnotator.java"}

If the above code is copied at this stage of the tutorial, then remove the line below the comment "** Tutorial step 18.3 …" The quick fix class in that line is not defined until later in the tutorial.

{type="tip"}

Register the Annotator

Using the com.intellij.annotator extension point in the plugin configuration file, register the Simple Language annotator class with the IntelliJ Platform:

  <extensions defaultExtensionNs="com.intellij">
    <annotator language="JAVA" implementationClass="org.intellij.sdk.language.SimpleAnnotator"/>
  </extensions>

Run the Project

Run the plugin by using the Gradle runIde task.

As a test, define the following Java file containing a Simple Language prefix:value pair:

public class Test {
    public static void main(String[] args) {
        System.out.println("simple:website");
    }
}

Open this Java file in an IDE Development Instance running the simple_language_plugin to check if the IDE resolves a property:

{width="800"}

If the property is an undefined name, the annotator flags the code with an error.

{width="800"}

Try changing the Simple Language color settings to differentiate the annotation from the default language color settings.