Add ktfmt option to KotlinGradleExtension

plugin-gradle/CHANGES.md

@@ -3,6 +3,7 @@
 We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (starting after version `3.27.0`).
 
 ## [Unreleased]
+* Support for ktfmt in KotlinGradleExtension ([#583](https://github.com/diffplug/spotless/pull/583))
 
 ## [4.0.1] - 2020-05-21
 ### Fixed

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/KotlinGradleExtension.java

@@ -22,6 +22,7 @@
 import com.diffplug.common.collect.ImmutableSortedMap;
 import com.diffplug.spotless.FormatterStep;
 import com.diffplug.spotless.kotlin.KtLintStep;
+import com.diffplug.spotless.kotlin.KtfmtStep;
 
 public class KotlinGradleExtension extends FormatExtension {
 	private static final String GRADLE_KOTLIN_DSL_FILE_EXTENSION = "*.gradle.kts";
@@ -65,6 +66,33 @@ private FormatterStep createStep() {
 		}
 	}
 
+	/** Uses the [ktfmt](https://github.com/facebookincubator/ktfmt) jar to format source code. */
+	public KtfmtConfig ktfmt() {
+		return ktfmt(KtfmtStep.defaultVersion());
+	}
+
+	/**
+	 * Uses the given version of [ktfmt](https://github.com/facebookincubator/ktfmt) to format source
+	 * code.
+	 */
+	public KtfmtConfig ktfmt(String version) {
+		Objects.requireNonNull(version);
+		return new KtfmtConfig(version);
+	}
+
+	public class KtfmtConfig {
+		final String version;
+
+		KtfmtConfig(String version) {
+			this.version = Objects.requireNonNull(version);
+			addStep(createStep());
+		}
+
+		private FormatterStep createStep() {
+			return KtfmtStep.create(version, GradleProvisioner.fromProject(getProject()));
+		}
+	}
+
 	@Override
 	protected void setupTask(SpotlessTask task) {
 		if (target == null) {

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/KotlinGradleExtensionTest.java

@@ -22,6 +22,8 @@
 import org.gradle.testkit.runner.BuildResult;
 import org.junit.Test;
 
+import com.diffplug.spotless.JreVersion;
+
 public class KotlinGradleExtensionTest extends GradleIntegrationTest {
 	@Test
 	public void integration() throws IOException {
@@ -109,6 +111,28 @@ public void indentStep() throws IOException {
 		assertThat(result.getOutput()).contains("Unexpected indentation (4) (it should be 6)");
 	}
 
+	@Test
+	public void integration_ktfmt() throws IOException {
+		if (JreVersion.thisVm() == JreVersion._8) {
+			// ktfmt's dependency, google-java-format 1.8 requires a minimum of JRE 11+.
+			return;
+		}
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'nebula.kotlin' version '1.0.6'",
+				"    id 'com.diffplug.gradle.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"spotless {",
+				"    kotlinGradle {",
+				"        ktfmt()",
+				"    }",
+				"}");
+		setFile("configuration.gradle.kts").toResource("kotlin/ktfmt/basic.dirty");
+		gradleRunner().withArguments("spotlessApply").build();
+		assertFile("configuration.gradle.kts").sameAsResource("kotlin/ktfmt/basic.clean");
+	}
+
 	@Test
 	public void integration_lint_script_files_without_top_level_declaration() throws IOException {
 		setFile("build.gradle").toLines(