Make JarHell task cacheable (#42551)

Author: mark-vieira

buildSrc/src/main/groovy/org/elasticsearch/gradle/precommit/PrecommitTasks.groovy

@@ -107,14 +107,12 @@ class PrecommitTasks {
     }
 
     private static Task configureJarHell(Project project) {
-        Task task = project.tasks.create('jarHell', JarHellTask.class)
-        task.classpath = project.sourceSets.test.runtimeClasspath
-        if (project.plugins.hasPlugin(ShadowPlugin)) {
-            task.classpath += project.configurations.bundle
+        return project.tasks.create('jarHell', JarHellTask) { task ->
+            task.classpath = project.sourceSets.test.runtimeClasspath
+            if (project.plugins.hasPlugin(ShadowPlugin)) {
+                task.classpath += project.configurations.bundle
+            }
         }
-        task.dependsOn(project.sourceSets.test.classesTaskName)
-        task.javaHome = project.runtimeJavaHome
-        return task
     }
 
     private static Task configureThirdPartyAudit(Project project) {

buildSrc/src/main/java/org/elasticsearch/gradle/precommit/JarHellTask.java

@@ -21,19 +21,20 @@
 
 import org.elasticsearch.gradle.LoggedExec;
 import org.gradle.api.file.FileCollection;
-import org.gradle.api.tasks.Classpath;
-import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.CacheableTask;
+import org.gradle.api.tasks.CompileClasspath;
 import org.gradle.api.tasks.TaskAction;
 
+import java.io.File;
+
 /**
  * Runs CheckJarHell on a classpath.
  */
+@CacheableTask
 public class JarHellTask extends PrecommitTask {
 
     private FileCollection classpath;
 
-    private Object javaHome;
-
     public JarHellTask() {
         setDescription("Runs CheckJarHell on the configured classpath");
     }
@@ -42,23 +43,15 @@ public JarHellTask() {
     public void runJarHellCheck() {
         LoggedExec.javaexec(getProject(), spec -> {
             spec.classpath(getClasspath());
-            spec.executable(getJavaHome() + "/bin/java");
             spec.setMain("org.elasticsearch.bootstrap.JarHell");
         });
     }
 
-    @Input
-    public Object getJavaHome() {
-        return javaHome;
-    }
-
-    public void setJavaHome(Object javaHome) {
-        this.javaHome = javaHome;
-    }
-
-    @Classpath
+    // We use compile classpath normalization here because class implementation changes are irrelevant for the purposes of jar hell.
+    // We only care about the runtime classpath ABI here.
+    @CompileClasspath
     public FileCollection getClasspath() {
-        return classpath.filter(file -> file.exists());
+        return classpath.filter(File::exists);
     }
 
     public void setClasspath(FileCollection classpath) {