Support google-java-format 1.8+

[benkard]

In google-java-format 1.8, the signature of
RemoveUnusedImports#removeUnusedImports changed and the
RemoveUnusedImports$JavadocOnlyImports class was removed entirely.
With this patch, GoogleJavaFormatStep detects which version of the
method is available and calls the right one.

Fixes #562.

[nedtwigg]

@diffplug/spotless Just FYI, this is the first PR we have received where the formatter requires Java 11+, and there are more coming (#547). As a result, we now need our tests to run on Java 11.

This PR represents the minimal effort needed to merge support for google-java-format 1.8 with tests. We now run the whole build on both 8 and 11. The only things I disabled on 11 are things which are broken there, namely

• plugin-maven
• javadoc generation
• spotbugs (I think already fixed in newer spotbugs)

The trickier part is that now there are some tests which you can't run on 8, because they'll break. Also, Gradle 5.0 is the oldest that can run on Java 11, so you can't run old-gradle-tests on 11.

I'm very open to PRs for a more comprehensive solution, but I think it's fine to play whack-a-mole until a pattern merges. Here's the gist of the 8 / 11 test infrastructure I put in:

spotless/testlib/src/main/java/com/diffplug/spotless/JreVersion.java

Lines 20 to 23 in 11f58d8

	public enum JreVersion {
	_8, _11;
	public static JreVersion thisVm() {

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

Lines 30 to 35 in 11f58d8

	@Test
	public void behavior18() throws Exception {
	if (JreVersion.thisVm() == JreVersion._8) {
	// google-java-format requires JRE 11+
	return;
	}

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

Lines 60 to 78 in 11f58d8

	/**
	* For Java 11+, Gradle 5 is the minimum.
	* So if you ask for less than Gradle 5, you get it on Java 8, but on Java 11 you get promoted to Gradle 5.
	* If you ask for more than Gradle 5, you'll definitely get it.
	*/
	protected static String requestGradleForJre8and11(String ver) {
	JreVersion jre = JreVersion.thisVm();
	// @formatter:off
	switch (jre) {
	case _8: return ver;
	case _11: return Double.parseDouble(ver) < 5.0 ? "5.0" : ver;
	default: throw new IllegalStateException("Spotless build is only supported on Java 8 and Java 11");
	}
	// @formatter:on
	}
	protected final GradleRunner gradleRunner() throws IOException {
	return GradleRunner.create()
	.withGradleVersion(requestGradleForJre8and11("2.14"))

[nedtwigg]

Released in plugin-gradle 3.29.0, and plugin-maven 1.31.0