obecker · Copilot · Jul 2, 2025 · Jul 2, 2025 · Jul 2, 2025
diff --git a/plugin-gradle/demo/allowed.gradle b/plugin-gradle/demo/allowed.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/cycle.gradle b/plugin-gradle/demo/cycle.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/default.gradle b/plugin-gradle/demo/default.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 // should detect the cycle between demo.cycle.a and demo.cycle.b without any custom configuration
diff --git a/plugin-gradle/demo/disallowed.gradle b/plugin-gradle/demo/disallowed.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/error-ignoring-list.gradle b/plugin-gradle/demo/error-ignoring-list.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/error-ignoring-map.gradle b/plugin-gradle/demo/error-ignoring-map.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/error-illegal-pattern.gradle b/plugin-gradle/demo/error-illegal-pattern.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/error-missing-pattern.gradle b/plugin-gradle/demo/error-missing-pattern.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/error-no-java-plugin.gradle b/plugin-gradle/demo/error-no-java-plugin.gradle
@@ -0,0 +1,8 @@
+plugins {
+    id 'de.obqo.decycle'
+}
+
+// This simulates a project without the java plugin - it should fail with a meaningful error
+decycle {
+    excluding 'demo.cycle.**'
+}
diff --git a/plugin-gradle/demo/ignoreFailures.gradle b/plugin-gradle/demo/ignoreFailures.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/ignoring-from.gradle b/plugin-gradle/demo/ignoring-from.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/ignoring-kt.gradle.kts b/plugin-gradle/demo/ignoring-kt.gradle.kts
@@ -1,4 +1,5 @@
 plugins {
+    id("java")
     id("de.obqo.decycle")
 }
 

diff --git a/plugin-gradle/demo/ignoring-to.gradle b/plugin-gradle/demo/ignoring-to.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/ignoring.gradle b/plugin-gradle/demo/ignoring.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/multiple.gradle b/plugin-gradle/demo/multiple.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/reportsDisabled.gradle b/plugin-gradle/demo/reportsDisabled.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/slices-cycle.gradle b/plugin-gradle/demo/slices-cycle.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/source-sets.gradle b/plugin-gradle/demo/source-sets.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/success.gradle b/plugin-gradle/demo/success.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/demo/test-sources-kt.gradle.kts b/plugin-gradle/demo/test-sources-kt.gradle.kts
@@ -1,4 +1,5 @@
 plugins {
+    id("java")
     id("de.obqo.decycle")
 }
 

diff --git a/plugin-gradle/demo/test-sources.gradle b/plugin-gradle/demo/test-sources.gradle
@@ -1,4 +1,5 @@
 plugins {
+    id 'java'
     id 'de.obqo.decycle'
 }
 

diff --git a/plugin-gradle/src/main/groovy/de/obqo/decycle/gradle/DecyclePlugin.groovy b/plugin-gradle/src/main/groovy/de/obqo/decycle/gradle/DecyclePlugin.groovy
@@ -14,7 +14,6 @@ class DecyclePlugin implements Plugin<Project> {
 
     @Override
     void apply(final Project project) {
-        project.apply plugin: 'java'
 
         Properties props = new Properties()
         getClass().classLoader.getResource("META-INF/gradle-plugins/de.obqo.decycle.properties").withInputStream { stream ->
@@ -35,6 +34,13 @@ class DecyclePlugin implements Plugin<Project> {
         workerClasspath.setDescription("The Decycle libraries to be used for this project")
 
         project.afterEvaluate {
+            // Ensure that a compatible plugin (java, java-library, android, etc.) is applied
+            if (!project.hasProperty('sourceSets')) {
+                throw new org.gradle.api.GradleException(
+                    "Decycle plugin requires a plugin that provides source sets (e.g., 'java', 'java-library', or Android plugins). " +
+                    "Please apply one of these plugins before applying the decycle plugin."
+                )
+            }
 
             project.dependencies {
                 decycle "de.obqo.decycle:decycle-lib:${toolVersion}"

diff --git a/plugin-gradle/src/test/java/de/obqo/decycle/gradle/DecyclePluginFunctionalTest.java b/plugin-gradle/src/test/java/de/obqo/decycle/gradle/DecyclePluginFunctionalTest.java
@@ -239,4 +239,11 @@ void shouldCachePreviousRun() {
         // then
         assertBuildResult(upToDateResult, TaskOutcome.UP_TO_DATE, "decycleMain");
     }
+
+    @Test
+    void shouldFailWhenNoCompatiblePluginApplied() {
+        final BuildResult result = buildAndFail("error-no-java-plugin.gradle");
+        assertBuildResult(result, TaskOutcome.FAILED, null)
+                .contains("Decycle plugin requires a plugin that provides source sets");
+    }
 }
diff --git a/plugin-gradle/src/test/java/de/obqo/decycle/gradle/DecyclePluginUnitTest.java b/plugin-gradle/src/test/java/de/obqo/decycle/gradle/DecyclePluginUnitTest.java
@@ -15,6 +15,7 @@ public class DecyclePluginUnitTest {
     @Test
     void pluginShouldAddTaskAndExtension() {
         Project project = ProjectBuilder.builder().build();
+        project.getPluginManager().apply("java");
         project.getPluginManager().apply("de.obqo.decycle");
 
         assertThat(project.getTasks().getByName("decycle")).isInstanceOf(Task.class);