Line markers help to annotate any code with icons on the gutter. These icons may provide navigation to related code.

8.1. Define a line marker provider

Let's annotate usages of our properties within Java code and provide navigation to the definition of these properties.

{% include /code_samples/simple_language_plugin/src/com/simpleplugin/SimpleLineMarkerProvider.java %}

More technical details for implementers

• Please return line marker info for exact element you were asked for. For example, do not return class marker info if getLineMarkerInfo() was called for a method.

• Please return relevant line marker info for as small element as possible. For example, do not return method marker for PsiMethod. Instead, return it for the PsiIdentifier which is a name of this method.

Even more technical details:

What happens when LineMarkerProvider returns something for too big PsiElement?

public class MyLineMarkerProvider implements LineMarkerProvider {
  public LineMarkerInfo getLineMarkerInfo(@NotNull PsiElement element) {
    if (element instanceof PsiMethod) return new LineMarkerInfo(element, ...);
    return null;
  }
}

Inspection (specifically, LineMarkersPass) for performance reasons queries all LineMarkerProviders in two passes:

• first pass for all elements in visible area

• second pass for all the rest elements

If providers return nothing for either area, its line markers are cleared. So if e.g. a method is half-visible (its name is visible but part of its body isn't) and some poorly written LineMarkerProvider returned info for the PsiMethod instead of PsiIdentifier then:

• the first pass removes line marker info because whole PsiMethod is not visible.

• the second pass tries to add line marker info back because LineMarkerProvider is called for the PsiMethod at last.

As a result, line marker icon would blink annoyingly. To fix this, rewrite LineMarkerProvider to return info for PsiIdentifier instead of PsiMethod:

public class MyLineMarkerProvider implements LineMarkerProvider {
  public LineMarkerInfo getLineMarkerInfo(@NotNull PsiElement element) {
    if (element instanceof PsiIdentifier && element.getParent() instanceof PsiMethod) return new LineMarkerInfo(element, ...);
    return null;
  }
}

8.2. Register the line marker provider

<codeInsight.lineMarkerProvider language="JAVA" implementationClass="com.simpleplugin.SimpleLineMarkerProvider"/>

8.3. Run the project

Now you see the icon on the gutter and can navigate to the property definition.

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