Support up-to-date checking of Format task

See gh-323

Author: larsgrefer

spring-javaformat-gradle/spring-javaformat-gradle-plugin/src/main/java/io/spring/javaformat/gradle/tasks/Format.java

@@ -19,6 +19,11 @@
 import java.io.IOException;
 
 import org.gradle.api.GradleException;
+import org.gradle.api.file.FileTree;
+import org.gradle.api.tasks.InputFiles;
+import org.gradle.api.tasks.OutputFiles;
+import org.gradle.api.tasks.PathSensitive;
+import org.gradle.api.tasks.PathSensitivity;
 import org.gradle.api.tasks.TaskAction;
 
 import io.spring.javaformat.formatter.FileEdit;
@@ -51,4 +56,15 @@ public void format() throws IOException, InterruptedException {
 		}
 	}
 
+	@Override
+	@InputFiles
+	@PathSensitive(PathSensitivity.RELATIVE)
+	public FileTree getSource() {
+		return super.getSource();
+	}
+
+	@OutputFiles
+	public FileTree getOutputFiles() {
+		return super.getSource();
+	}
 }

spring-javaformat-gradle/spring-javaformat-gradle-plugin/src/test/java/io/spring/javaformat/gradle/FormatTaskTests.java

@@ -21,6 +21,7 @@
 import java.nio.file.Files;
 
 import org.gradle.testkit.runner.BuildResult;
+import org.gradle.testkit.runner.GradleRunner;
 import org.gradle.testkit.runner.TaskOutcome;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -50,6 +51,24 @@ public void checkOk() throws IOException {
 		assertThat(formattedContent).contains("class Simple {").contains("	public static void main");
 	}
 
+	@Test
+	public void checkUpTpDate() throws IOException {
+		GradleRunner runner = this.gradleBuild.source("src/test/resources/format").prepareRunner("format");
+
+		// 1) Actually format the sources.
+		BuildResult result1 = runner.build();
+		assertThat(result1.task(":formatMain").getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+
+		// 2) No-op reformat the sources
+		// Not up-to-date yet because 1) changed the sources.
+		BuildResult result2 = runner.build();
+		assertThat(result2.task(":formatMain").getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+
+		// 3) Now we should be up-to-date since 2) was effectively a no-op
+		BuildResult result3 = runner.build();
+		assertThat(result3.task(":formatMain").getOutcome()).isEqualTo(TaskOutcome.UP_TO_DATE);
+	}
+
 	@Test
 	public void checkSpacesOk() throws IOException {
 		BuildResult result = this.gradleBuild.source("src/test/resources/format-spaces").build("format");