Support using the plugin with Java 8

[fhoeben]

What happened?

I tried to add the plugin to our project FitNesse. I added the plugin to the plugins block and added the following config

jdks {
  jdk(8) {
    distribution = 'azul-zulu'
    jdkVersion = '8.64.0.19'
  }
}

javaVersions {
  libraryTarget = 8
}

When I tried to build I got:

java.lang.UnsupportedClassVersionError: com/palantir/gradle/jdks/JdksPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
com/palantir/gradle/jdks/JdksPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

What did you want to happen?

I would have liked to be able to use this plugin also when my gradle is using Java 8

[arlaneenalra]

It looks like:

gradle-jdks/gradle-jdks/src/main/java/com/palantir/gradle/jdks/JdkManager.java

Lines 192 to 208 in d598c41

	private Path findJavaHome(Path temporaryJdkPath) {
	try (Stream<Path> files = Files.walk(temporaryJdkPath)) {
	return files.filter(file -> Files.isRegularFile(file)
	// macos JDKs have a `bin/java` symlink to `Contents/Home/bin/java`
	&& !Files.isSymbolicLink(file)
	&& file.endsWith(Paths.get("bin", SystemTools.java())))
	.findFirst()
	// JAVA_HOME/bin/java
	.orElseThrow(() -> new RuntimeException("Failed to find java home in " + temporaryJdkPath))
	// JAVA_HOME/bin
	.getParent()
	// JAVA_HOME
	.getParent();
	} catch (IOException e) {
	throw new RuntimeException("Failed to find java home in " + temporaryJdkPath, e);
	}
	}

finds the bare JRE instead of the JDK

2023-04-02T17:27:21.811-0500 [INFO] [org.gradle.api.Project] Moving JDK azul-zulu 8.68.0.21-8.0.362 (999007504b0ffb2e) home /Users/jules/.gradle/gradle-jdks/azul-zulu-8.68.0.21-8.0.362-999007504b0ffb2e.in-progress-7bb4e4aa/zulu8.68.0.21-ca-jdk8.0.362-macosx_aarch64/zulu-8.jdk/Contents/Home/jre to /Users/jules/.gradle/gradle-jdks/azul-zulu-8.68.0.21-8.0.362-999007504b0ffb2e

I'm not entirely sure why .. but that's likely what's breaking things here ..

This code appears to be looking for java instead of javac

gradle-jdks/gradle-jdks/src/main/java/com/palantir/gradle/jdks/SystemTools.java

Lines 22 to 27 in d598c41

	static String java() {
	if (Os.current() == Os.WINDOWS) {
	return "java.exe";
	}
	return "java";
	}

Which seems to contribute to the problem... hmmm

[CRogers]

java.lang.UnsupportedClassVersionError: com/palantir/gradle/jdks/JdksPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

This is saying the JDK you are running Gradle with is a Java 8 JDK, and this plugin (all our gradle plugins + libraries) require Java 11 to run. You'll need to upgrade to JDK you use (Java 8 has been end of life since 31 Mar 2022). Eventually we'll start requiring Java 17 for Gradle plugins and libraries.

An upcoming feature of this project will be managing the JDK used to run Gradle, which will make this much easier to roll out to users, as it will automatically install the right JDK even if they have no JDKs installed. I cannot give any definitive timeline when we actually get around to building that feature though, although we kinda need it soon internally.