Lazily initialize GitRatchetGradle to avoid loading JGit at configuration time

GitRatchetGradle is instantiated eagerly when SpotlessTaskService is
created, which happens during Gradle configuration. Its static
initializer installs a custom JGit SystemReader that reads
~/.gitconfig. This causes Gradle's configuration cache to fingerprint
the file even when no Spotless tasks are requested.

Defer instantiation to getRatchet(), which is only called during task
execution. This avoids loading JGit classes and reading git config
files at configuration time.

Author: joshfriend

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

@@ -99,9 +99,12 @@ void registerApplyAlreadyRan(SpotlessApply task) {
 	}
 
 	// <GitRatchet>
-	private final GitRatchetGradle ratchet = new GitRatchetGradle();
+	private GitRatchetGradle ratchet;
 
 	GitRatchetGradle getRatchet() {
+		if (ratchet == null) {
+			ratchet = new GitRatchetGradle();
+		}
 		return ratchet;
 	}
 
@@ -112,7 +115,9 @@ public void onFinish(FinishEvent var1) {
 
 	@Override
 	public void close() throws Exception {
-		ratchet.close();
+		if (ratchet != null) {
+			ratchet.close();
+		}
 	}
 	// </GitRatchet>
 

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

@@ -17,6 +17,7 @@
 
 import java.io.IOException;
 
+import org.assertj.core.api.Assertions;
 import org.gradle.testkit.runner.GradleRunner;
 import org.junit.jupiter.api.Test;
 
@@ -60,6 +61,32 @@ public void helpConfiguresIfTasksAreCreated() throws IOException {
 		gradleRunner().withArguments("help").build();
 	}
 
+	@Test
+	public void jgitNotLoadedDuringConfiguration() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"apply plugin: 'java'",
+				"spotless {",
+				"    java {",
+				"        googleJavaFormat()",
+				"    }",
+				"}",
+				"",
+				"// Detect if JGit's SystemReader was replaced during configuration.",
+				"// GitRatchetGradle.redirectJGitExecutions() replaces it, so if it",
+				"// is still the default instance, JGit was not loaded.",
+				"def sr = org.eclipse.jgit.util.SystemReader.getInstance()",
+				"if (sr.getClass().getName().contains('DelegatingSystemReader')) {",
+				"    throw new GradleException('JGit SystemReader was replaced during configuration')",
+				"}");
+		setFile("src/main/java/test.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+		String output = gradleRunner().withArguments("help").build().getOutput();
+		Assertions.assertThat(output).doesNotContain("JGit SystemReader was replaced during configuration");
+	}
+
 	@Test
 	public void multipleRuns() throws IOException {
 		setFile("build.gradle").toLines(