fix: Add main sourceSet output to the inputs

Fixes #24

build.gradle

@@ -56,6 +56,11 @@ dependencies {
 
     compileOnly "io.smallrye:jandex:$jandexVersion"
     api "org.kordamp.gradle:base-gradle-plugin:$kordampPluginVersion"
+
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.2'
+    testImplementation 'org.assertj:assertj-core:3.11.1'
+
+    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.2'
 }
 
 processResources {
@@ -68,4 +73,26 @@ processResources {
             jandexVersion: jandexVersion
         )
     }
-}
+}
+
+// Add a source set for the functional test suite
+sourceSets {
+    functionalTest {
+    }
+}
+
+gradlePlugin.testSourceSets(sourceSets.functionalTest)
+configurations.functionalTestImplementation.extendsFrom(configurations.testImplementation)
+configurations.functionalTestRuntimeOnly.extendsFrom(configurations.testRuntimeOnly)
+
+// Add a task to run the functional tests
+tasks.register('functionalTest', Test) {
+    testClassesDirs = sourceSets.functionalTest.output.classesDirs
+    classpath = sourceSets.functionalTest.runtimeClasspath
+    useJUnitPlatform()
+}
+
+tasks.named('check') {
+    // Run the functional tests as part of `check`
+    dependsOn(tasks.functionalTest)
+}

src/functionalTest/groovy/org/kordamp/gradle/plugin/jandex/JandexPluginPluginFunctionalTest.groovy

@@ -0,0 +1,116 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Copyright 2019-2023 Andres Almiray.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.kordamp.gradle.plugin.jandex
+
+import org.assertj.core.api.Assertions
+import org.gradle.testkit.runner.BuildResult
+import org.gradle.testkit.runner.GradleRunner
+import org.gradle.testkit.runner.TaskOutcome
+import org.junit.jupiter.api.Test
+
+class JandexPluginPluginFunctionalTest  {
+
+    private File projectDir
+
+    private getBuildFile() {
+        new File(projectDir, "build.gradle")
+    }
+
+    private getSettingsFile() {
+        new File(projectDir, "settings.gradle")
+    }
+
+    private getSourceFileAClass() {
+        new File(projectDir, 'src/main/java/com/sample').mkdirs()
+        new File(projectDir, 'src/main/java/com/sample/AClass.java')
+    }
+
+    @Test
+    void testApply() {
+        projectDir = new File("build/functionalTestFixture/apply_${System.currentTimeMillis()}")
+        projectDir.mkdirs()
+
+        def indexFile = new File(projectDir, 'build/resources/main/META-INF/jandex.idx')
+        Assertions.assertThat(indexFile).doesNotExist();
+
+        settingsFile.text = ""
+        buildFile.text = """
+plugins {
+    id 'org.kordamp.gradle.jandex'
+}
+
+repositories {
+    mavenCentral()
+}
+"""
+
+        sourceFileAClass.text = """
+package com.sample;
+
+public class AClass {
+	public void sayHi() {
+		System.out.println("hi");
+	}
+}
+"""
+        def runner1 = createRunner()
+        def result1 = runner1.build()
+        Assertions.assertThat(result1.task(':jandex').outcome).isEqualTo(TaskOutcome.SUCCESS);
+        Assertions.assertThat(indexFile).exists();
+        def content1 = indexFile.getText("UTF-8")
+        Assertions.assertThat(content1).contains("sayHi");
+
+        //Re run without any changes, to be sure the task is up-to-date:
+        def runner2 = createRunner()
+        def result2 = runner2.build()
+        Assertions.assertThat(result2.task(':jandex').outcome).isEqualTo(TaskOutcome.UP_TO_DATE);
+
+        //Modify source file, and verify jandex was executed again:
+        sourceFileAClass.text = """
+package com.sample;
+
+public class AClass {
+	public void sayHello() {
+		System.out.println("hello");
+	}
+}
+"""
+        def runner3 = createRunner()
+        def result3 = runner3.build()
+        Assertions.assertThat(result3.task(':jandex').outcome).isEqualTo(TaskOutcome.SUCCESS);
+        Assertions.assertThat(indexFile).exists();
+        def content3 = indexFile.getText("UTF-8")
+        Assertions.assertThat(content3)
+            .isNotEqualTo(content1)
+            .contains("sayHello");
+
+        //Re run without any changes, to be sure the task is up-to-date:
+        def runner4 = createRunner()
+        def result4 = runner4.build()
+        Assertions.assertThat(result4.task(':jandex').outcome).isEqualTo(TaskOutcome.UP_TO_DATE);
+    }
+
+    def createRunner() {
+        def runner = GradleRunner.create()
+        runner.forwardOutput()
+        runner.withPluginClasspath()
+        runner.withArguments("jandex", "--stacktrace")
+        runner.withProjectDir(projectDir)
+        return runner
+    }
+}

src/main/groovy/org/kordamp/gradle/plugin/jandex/JandexPlugin.groovy

@@ -73,6 +73,9 @@ class JandexPlugin implements Plugin<Project> {
                     t.processResourcesTask = project.tasks.named('processResources', Copy)
                     t.layout.set(project.layout)
                     t.sourceSets.addAll(project.extensions.findByType(SourceSetContainer))
+                    if (t.resolvedProcessDefaultFileSet.get()) {
+                        t.inputs.files(t.sourceSets.findByName('main').output.classesDirs*.absolutePath.flatten())
+                    }
                 }
             })