Extract logic of detecting a Stapler view into extension point

gradle.properties

@@ -4,5 +4,5 @@ ideaVersion=2021.3
 sinceIdeaVersion=
 # see https://plugins.jetbrains.com/docs/intellij/tools-gradle-intellij-plugin.html#intellij-extension-type for list of accepted types
 ideaType=IC
-platformPlugins=properties,java
+platformPlugins=properties,java,org.intellij.groovy
 intellijPublishToken=

src/main/java/io/jenkins/stapler/idea/facets/groovy/GroovyViewPredicate.java

@@ -0,0 +1,12 @@
+package io.jenkins.stapler.idea.facets.groovy;
+
+import com.intellij.psi.PsiFile;
+import org.jetbrains.plugins.groovy.GroovyFileType;
+import org.kohsuke.stapler.idea.extension.JavaStructureViewExtension;
+
+public class GroovyViewPredicate implements JavaStructureViewExtension.StaplerViewPredicate {
+    @Override
+    public boolean test(PsiFile psiFile) {
+        return psiFile.getFileType() == GroovyFileType.GROOVY_FILE_TYPE;
+    }
+}

src/main/java/io/jenkins/stapler/idea/facets/jelly/JellyViewPredicate.java

@@ -0,0 +1,12 @@
+package io.jenkins.stapler.idea.facets.jelly;
+
+import com.intellij.psi.PsiFile;
+import org.kohsuke.stapler.idea.extension.JavaStructureViewExtension;
+import org.kohsuke.stapler.idea.language.JellyFileType;
+
+public class JellyViewPredicate implements JavaStructureViewExtension.StaplerViewPredicate {
+    @Override
+    public boolean test(PsiFile psiFile) {
+        return psiFile.getFileType() == JellyFileType.INSTANCE;
+    }
+}

src/main/java/org/kohsuke/stapler/idea/extension/JavaStructureViewExtension.java

@@ -1,15 +1,16 @@
 package org.kohsuke.stapler.idea.extension;
 
 import com.intellij.ide.structureView.StructureViewTreeElement;
+import com.intellij.openapi.extensions.ExtensionPointName;
 import com.intellij.psi.JavaPsiFacade;
 import com.intellij.psi.PsiClass;
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiFile;
 import com.intellij.psi.PsiPackage;
-import org.kohsuke.stapler.idea.psi.JellyFile;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Predicate;
 
 /**
  * Additional jelly files in java structure view
@@ -19,6 +20,10 @@
  */
 public class JavaStructureViewExtension extends AbstractStructureViewExtension {
 
+    public interface StaplerViewPredicate extends Predicate<PsiFile> {
+        ExtensionPointName<Predicate<PsiFile>> EP_NAME =
+            ExtensionPointName.create("Stapler plugin for IntelliJ IDEA.staplerViewPredicate");
+    }
     @Override
     public Class<? extends PsiElement> getType() {
         return PsiClass.class;
@@ -32,9 +37,10 @@ public StructureViewTreeElement[] getChildren(PsiElement parent) {
             PsiPackage psiPackage = JavaPsiFacade.getInstance(parent.getProject())
                                                  .findPackage(qualifiedClassName);
             if (psiPackage != null) {
+                Predicate<PsiFile> isView = StaplerViewPredicate.EP_NAME.extensions().reduce(Predicate::or).orElseGet(() -> psiFile -> false);
                 PsiFile[] maybeViewFiles = psiPackage.getFiles(getCurrentScope(parent));
                 for (PsiFile file : maybeViewFiles) {
-                    if (file instanceof JellyFile) {
+                    if (isView.test(file)) {
                         files.add(new LeafPsiStructureViewTreeElement(file));
                     }
                 }

src/main/resources/META-INF/jenkins-groovy.xml

@@ -0,0 +1,5 @@
+<idea-plugin>
+  <extensions defaultExtensionNs="Stapler plugin for IntelliJ IDEA">
+    <staplerViewPredicate implementation="io.jenkins.stapler.idea.facets.groovy.GroovyViewPredicate" />
+  </extensions>
+</idea-plugin>

src/main/resources/META-INF/plugin.xml

@@ -8,6 +8,14 @@
 <!--  <version>1.8</version>-->
 <!--  <idea-version since-build="110.00"/>-->
 
+  <extensionPoints>
+    <extensionPoint name="staplerViewPredicate" interface="org.kohsuke.stapler.idea.extension.JavaStructureViewExtension$StaplerViewPredicate"/>
+  </extensionPoints>
+
+  <extensions defaultExtensionNs="Stapler plugin for IntelliJ IDEA">
+    <staplerViewPredicate implementation="io.jenkins.stapler.idea.facets.jelly.JellyViewPredicate" />
+  </extensions>
+
   <extensions defaultExtensionNs="com.intellij">
     <!--
       REFERENCE:
@@ -137,5 +145,6 @@
   <depends>com.intellij.properties</depends>
   <!-- this is needed for language injection -->
   <!--<depends>org.intellij.intelliLang</depends>-->
+  <depends optional="true" config-file="jenkins-groovy.xml">org.intellij.groovy</depends>
 
 </idea-plugin>