google-java-format now uses the latest default available for the curr…

…ent JRE. If the user is using an old JRE and has a failure, it lets them know that they might get a fix by updating to a newer JRE to get the latest GJF.

lib/src/main/java/com/diffplug/spotless/java/GoogleJavaFormatStep.java

@@ -32,7 +32,6 @@ public class GoogleJavaFormatStep {
 	// prevent direct instantiation
 	private GoogleJavaFormatStep() {}
 
-	private static final String DEFAULT_VERSION = "1.7";
 	private static final String DEFAULT_STYLE = "GOOGLE";
 	static final String NAME = "google-java-format";
 	static final String MAVEN_COORDINATE = "com.google.googlejavaformat:google-java-format:";
@@ -75,10 +74,25 @@ public static FormatterStep create(String version, String style, Provisioner pro
 				State::createFormat);
 	}
 
+	private static final int JRE_VERSION;
+
+	static {
+		String jre = System.getProperty("java.version");
+		if (jre.startsWith("1.8")) {
+			JRE_VERSION = 8;
+		} else {
+			JRE_VERSION = Integer.parseInt(jre.substring(0, jre.indexOf('.')));
+		}
+	}
+
+	/** On JRE 11+, returns `1.9`. On earlier JREs, returns `1.7`. */
 	public static String defaultVersion() {
-		return DEFAULT_VERSION;
+		return JRE_VERSION >= 11 ? LATEST_VERSION_JRE_11 : LATEST_VERSION_JRE_8;
 	}
 
+	private static final String LATEST_VERSION_JRE_8 = "1.7";
+	private static final String LATEST_VERSION_JRE_11 = "1.9";
+
 	public static String defaultStyle() {
 		return DEFAULT_STYLE;
 	}
@@ -130,20 +144,18 @@ FormatterFunc createFormat() throws Exception {
 			Class<?> importOrdererClass = classLoader.loadClass(IMPORT_ORDERER_CLASS);
 			Method importOrdererMethod = importOrdererClass.getMethod(IMPORT_ORDERER_METHOD, String.class);
 
-			return input -> {
+			return suggestJre11(input -> {
 				String formatted = (String) formatterMethod.invoke(formatter, input);
 				String removedUnused = removeUnused.apply(formatted);
 				String sortedImports = (String) importOrdererMethod.invoke(null, removedUnused);
 				return fixWindowsBug(sortedImports, version);
-			};
+			});
 		}
 
 		FormatterFunc createRemoveUnusedImportsOnly() throws Exception {
 			ClassLoader classLoader = jarState.getClassLoader();
-
 			Function<String, String> removeUnused = constructRemoveUnusedFunction(classLoader);
-
-			return input -> fixWindowsBug(removeUnused.apply(input), version);
+			return suggestJre11(input -> fixWindowsBug(removeUnused.apply(input), version));
 		}
 
 		private static Function<String, String> constructRemoveUnusedFunction(ClassLoader classLoader)
@@ -204,4 +216,19 @@ static String fixWindowsBug(String input, String version) {
 		}
 		return input;
 	}
+
+	private static FormatterFunc suggestJre11(FormatterFunc in) {
+		if (JRE_VERSION >= 11) {
+			return in;
+		} else {
+			return unixIn -> {
+				try {
+					return in.apply(unixIn);
+				} catch (Exception e) {
+					throw new Exception("You are running Spotless on JRE " + JRE_VERSION + ", which limits you to google-java-format " + LATEST_VERSION_JRE_8 + "\n"
+							+ "If you upgrade your build JVM to 11+, then you can use google-java-format " + LATEST_VERSION_JRE_11 + ", which may have fixed this problem.", e);
+				}
+			};
+		}
+	}
 }

testlib/src/main/resources/java/googlejavaformat/TextBlock.clean

@@ -0,0 +1,14 @@
+import mylib.UsedA;
+import mylib.UsedB;
+
+public class Java {
+  public static void main(String[] args) {
+    var a = """
+      Howdy
+      Partner!
+      """;
+    System.out.println(a);
+    UsedB.someMethod();
+    UsedA.someMethod();
+  }
+}

testlib/src/main/resources/java/googlejavaformat/TextBlock.dirty

@@ -0,0 +1,15 @@
+
+import mylib.UsedA;
+import mylib.UsedB;
+
+public class Java {
+  public static void main(String[] args) {
+      var a = """
+      Howdy
+      Partner!
+      """;
+    System.out.println(a);
+    UsedB.someMethod();
+    UsedA.someMethod();
+  }
+}

testlib/src/test/java/com/diffplug/spotless/java/GoogleJavaFormatStepTest.java

@@ -15,6 +15,8 @@
  */
 package com.diffplug.spotless.java;
 
+import java.lang.reflect.InvocationTargetException;
+
 import org.junit.Assert;
 import org.junit.Test;
 
@@ -27,8 +29,30 @@
 import com.diffplug.spotless.TestProvisioner;
 
 public class GoogleJavaFormatStepTest extends ResourceHarness {
+	@Test
+	public void suggestJre11() throws Exception {
+		try (StepHarness step = StepHarness.forStep(GoogleJavaFormatStep.create(TestProvisioner.mavenCentral()))) {
+			if (JreVersion.thisVm() < 11) {
+				step.testException("java/googlejavaformat/TextBlock.dirty", throwable -> {
+					throwable.hasMessageStartingWith("You are running Spotless on JRE 8")
+							.hasMessageEndingWith(", which limits you to google-java-format 1.7\n"
+									+ "If you upgrade your build JVM to 11+, then you can use google-java-format 1.9, which may have fixed this problem.");
+				});
+			} else if (JreVersion.thisVm() < 13) {
+				step.testException("java/googlejavaformat/TextBlock.dirty", throwable -> {
+					throwable.isInstanceOf(InvocationTargetException.class)
+							.extracting(exception -> exception.getCause().getMessage()).asString().contains("7:18: error: unclosed string literal");
+				});
+			} else {
+				// JreVersion.thisVm() >= 13
+				step.testResource("java/googlejavaformat/TextBlock.dirty", "java/googlejavaformat/TextBlock.clean");
+			}
+		}
+	}
+
 	@Test
 	public void behavior18() throws Exception {
+		// google-java-format requires JRE 11+
 		JreVersion.assume11OrGreater();
 		FormatterStep step = GoogleJavaFormatStep.create("1.8", TestProvisioner.mavenCentral());
 		StepHarness.forStep(step)