fix(gradle): ensure Gradle 9 compatibility in FilesTaskV2

jib-gradle-plugin/src/main/java/com/google/cloud/tools/jib/gradle/skaffold/FilesTaskV2.java

@@ -91,16 +91,16 @@ public void listFiles() throws IOException {
 
     Set<File> projectDependencyJars = new HashSet<>();
     for (ProjectDependency projectDependency : projectDependencies) {
-      addProjectFiles(projectDependency.getDependencyProject());
+      Project dependentProject = getDependentProject(projectDependency);
+      addProjectFiles(dependentProject);
 
       // Keep track of project dependency jars for filtering out later
       String configurationName = projectDependency.getTargetConfiguration();
       if (configurationName == null) {
         configurationName = "default";
       }
-      Project dependencyProject = projectDependency.getDependencyProject();
       for (Configuration targetConfiguration :
-          dependencyProject.getConfigurations().getByName(configurationName).getHierarchy()) {
+          dependentProject.getConfigurations().getByName(configurationName).getHierarchy()) {
         for (PublishArtifact artifact : targetConfiguration.getArtifacts()) {
           projectDependencyJars.add(artifact.getFile());
         }
@@ -142,8 +142,7 @@ private void addGradleFiles(Project project) {
     skaffoldFilesOutput.addBuild(project.getBuildFile().toPath());
 
     // Add settings.gradle
-    if (GradleVersion.current().compareTo(GRADLE_9) < 0
-        && project.getGradle().getStartParameter().getSettingsFile() != null) {
+    if (isBeforeGradle9() && project.getGradle().getStartParameter().getSettingsFile() != null) {
       skaffoldFilesOutput.addBuild(
           project.getGradle().getStartParameter().getSettingsFile().toPath());
     } else if (Files.exists(projectPath.resolve(Settings.DEFAULT_SETTINGS_FILE))) {
@@ -212,7 +211,7 @@ private Set<ProjectDependency> findProjectDependencies(Project project) {
               // If this is a project dependency, save it
               ProjectDependency projectDependency = (ProjectDependency) dependency;
               if (!projectDependencies.contains(projectDependency)) {
-                projects.push(projectDependency.getDependencyProject());
+                projects.push(getDependentProject(projectDependency));
                 projectDependencies.add(projectDependency);
               }
             }
@@ -222,4 +221,36 @@ private Set<ProjectDependency> findProjectDependencies(Project project) {
     }
     return projectDependencies;
   }
+
+  /**
+   * Resolves a {@link ProjectDependency} to its corresponding {@link Project} instance.
+   *
+   * <p>This method handles the removal of {@code ProjectDependency.getDependencyProject()} in
+   * Gradle 9.0 by falling back to {@code getPath()} and resolving it via the project hierarchy.
+   *
+   * @param projectDependency the project dependency to resolve
+   * @return the resolved project
+   * @throws RuntimeException if the dependent project could not be resolved
+   */
+  private Project getDependentProject(ProjectDependency projectDependency) {
+    if (isBeforeGradle9()) {
+      return projectDependency.getDependencyProject();
+    }
+    try {
+      String path =
+          (String) projectDependency.getClass().getMethod("getPath").invoke(projectDependency);
+      return getProject().project(path);
+    } catch (ReflectiveOperationException ex) {
+      throw new RuntimeException("Failed to get dependent project from " + projectDependency, ex);
+    }
+  }
+
+  /**
+   * Checks if the current Gradle version is older than 9.0.
+   *
+   * @return {@code true} if the current Gradle version is less than 9.0, {@code false} otherwise
+   */
+  private static boolean isBeforeGradle9() {
+    return GradleVersion.current().compareTo(GRADLE_9) < 0;
+  }
 }

jib-gradle-plugin/src/test/java/com/google/cloud/tools/jib/gradle/skaffold/FilesTaskV2Test.java

@@ -46,6 +46,10 @@ public class FilesTaskV2Test {
 
   @ClassRule public static final TestProject multiTestProject = new TestProject("multi-service");
 
+  @ClassRule
+  public static final TestProject multiTestProjectGradle9 =
+      new TestProject("multi-service").withGradleVersion("9.0");
+
   @ClassRule
   public static final TestProject platformProject =
       new TestProject("platform").withGradleVersion("5.2");
@@ -188,4 +192,33 @@ public void testFilesTast_withConfigModifiers() throws IOException {
     assertPathListsAreEqual(
         ImmutableList.of(projectRoot.resolve("src/main/jib/bar")), result.getIgnore());
   }
+
+  @Test
+  public void testFilesTask_multiProjectComplexService_gradle9() throws IOException {
+    Path projectRoot = multiTestProjectGradle9.getProjectRoot();
+    Path complexServiceRoot = projectRoot.resolve("complex-service");
+    Path libRoot = projectRoot.resolve("lib");
+    SkaffoldFilesOutput result =
+        new SkaffoldFilesOutput(verifyTaskSuccess(multiTestProjectGradle9, "complex-service"));
+    assertPathListsAreEqual(
+        ImmutableList.of(
+            projectRoot.resolve("build.gradle"),
+            projectRoot.resolve("settings.gradle"),
+            projectRoot.resolve("gradle.properties"),
+            complexServiceRoot.resolve("build.gradle"),
+            libRoot.resolve("build.gradle")),
+        result.getBuild());
+    assertPathListsAreEqual(
+        ImmutableList.of(
+            complexServiceRoot.resolve("src/main/extra-resources-1"),
+            complexServiceRoot.resolve("src/main/extra-resources-2"),
+            complexServiceRoot.resolve("src/main/java"),
+            complexServiceRoot.resolve("src/main/other-jib"),
+            libRoot.resolve("src/main/resources"),
+            libRoot.resolve("src/main/java"),
+            complexServiceRoot.resolve(
+                "local-m2-repo/com/google/cloud/tools/tiny-test-lib/0.0.1-SNAPSHOT/tiny-test-lib-0.0.1-SNAPSHOT.jar")),
+        result.getInputs());
+    assertThat(result.getIgnore()).isEmpty();
+  }
 }