7. Annotator

Edit pageLast modified: 19 March 2025

Reference: Annotator

Code: SimpleAnnotator

Testing: 4. Annotator Test

tip

This page is part of multi-step Custom Language Support Tutorial. All previous steps must be executed in sequence for the code to work.

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.

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 the Gradle build script:

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.

note

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

final class SimpleAnnotator implements Annotator {

  // Define strings for the Simple language prefix - used for annotations, line markers, etc.
  public static final String SIMPLE_PREFIX_STR = "simple";
  public static final String SIMPLE_SEPARATOR_STR = ":";

  @Override
  public void annotate(@NotNull final PsiElement element, @NotNull AnnotationHolder holder) {
    // Ensure the PSI Element is an expression
    if (!(element instanceof PsiLiteralExpression literalExpression)) {
      return;
    }

    // Ensure the PSI element contains a string that starts with the prefix and separator
    String value = literalExpression.getValue() instanceof String ? (String) literalExpression.getValue() : null;
    if (value == null || !value.startsWith(SIMPLE_PREFIX_STR + SIMPLE_SEPARATOR_STR)) {
      return;
    }

    // Define the text ranges (start is inclusive, end is exclusive)
    // "simple:key"
    //  01234567890
    TextRange prefixRange = TextRange.from(element.getTextRange().getStartOffset(), SIMPLE_PREFIX_STR.length() + 1);
    TextRange separatorRange = TextRange.from(prefixRange.getEndOffset(), SIMPLE_SEPARATOR_STR.length());
    TextRange keyRange = new TextRange(separatorRange.getEndOffset(), element.getTextRange().getEndOffset() - 1);

    // highlight "simple" prefix and ":" separator
    holder.newSilentAnnotation(HighlightSeverity.INFORMATION)
        .range(prefixRange).textAttributes(DefaultLanguageHighlighterColors.KEYWORD).create();
    holder.newSilentAnnotation(HighlightSeverity.INFORMATION)
        .range(separatorRange).textAttributes(SimpleSyntaxHighlighter.SEPARATOR).create();


    // Get the list of properties for given key
    String key = value.substring(SIMPLE_PREFIX_STR.length() + SIMPLE_SEPARATOR_STR.length());
    List<SimpleProperty> properties = SimpleUtil.findProperties(element.getProject(), key);
    if (properties.isEmpty()) {
      holder.newAnnotation(HighlightSeverity.ERROR, "Unresolved property")
          .range(keyRange)
          .highlightType(ProblemHighlightType.LIKE_UNKNOWN_SYMBOL)
          // ** Tutorial step 19. - Add a quick fix for the string containing possible properties
          .withFix(new SimpleCreatePropertyQuickFix(key))
          .create();
    } else {
      // Found at least one property, force the text attributes to Simple syntax value character
      holder.newSilentAnnotation(HighlightSeverity.INFORMATION)
          .range(keyRange).textAttributes(SimpleSyntaxHighlighter.VALUE).create();
    }
  }

}

tip

If the above code is copied at this stage of the tutorial, then remove the line below the comment "** Tutorial step 19. …" The quick fix class in that line is not defined until later in the tutorial.

Register the Annotator

Using the com.intellij.annotator extension point in the plugin configuration file, register the Simple Language annotator class for JAVA language:

<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:

Annotator

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

Unresolved property

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