Improve support for Java 9+

This avoids the hardcoded message to stderr:

  [ERROR]: Cannot locate JRE jar in /Library/Java/JavaVirtualMachines/jdk-10.0.1.jdk/Contents/Home

And subsequent exception:

  java.lang.IllegalArgumentException: info cannot be null
    at org.fife.rsta.ac.java.JarManager.addClassFileSource(JarManager.java:157)
    at org.fife.rsta.ac.java.JarManager.addCurrentJreClassFileSource(JarManager.java:193)
    at org.scijava.ui.swing.script.languagesupport.JavaLanguageSupportPlugin.<init>(JavaLanguageSupportPlugin.java:56)

Which happens because the LibraryInfo.getJreJarInfo(File) method fails
to locate the main JRE JAR file, because Java 9+ does not have one --
rather, core classes are divided into modules in the jmods folder.

And allows the plugin to be created successfully anyway.

Fixes #29.

It also makes a best effort to find the "main JRE JAR" -- which for the
moment we point at jmods/java.base.jmod, one of many core modules --
and the sources archive in its new location, which is lib/src.zip.

Unfortunately, this logic is still insufficient to actually allow
RSyntaxTextArea's language support to display javadoc for core Java
classes with Java 9+, because the src.zip's internal directory structure
is now divided by module, which the library does not yet understand.

So really, an upstream fix will be needed to address this. Someday.

Author: ctrueden

src/main/java/org/scijava/ui/swing/script/languagesupport/JavaLanguageSupportPlugin.java

@@ -31,9 +31,13 @@
 
 package org.scijava.ui.swing.script.languagesupport;
 
+import java.io.File;
 import java.io.IOException;
 
 import org.fife.rsta.ac.java.JavaLanguageSupport;
+import org.fife.rsta.ac.java.buildpath.JarLibraryInfo;
+import org.fife.rsta.ac.java.buildpath.LibraryInfo;
+import org.fife.rsta.ac.java.buildpath.ZipSourceLocation;
 import org.scijava.plugin.Plugin;
 import org.scijava.ui.swing.script.LanguageSupportPlugin;
 import org.scijava.ui.swing.script.LanguageSupportService;
@@ -51,14 +55,51 @@ public class JavaLanguageSupportPlugin extends JavaLanguageSupport implements
 {
 
 	public JavaLanguageSupportPlugin() throws IOException {
-		super();
-
-		getJarManager().addCurrentJreClassFileSource();
+		final LibraryInfo info = getMainJreJarInfo();
+		if (info != null) getJarManager().addClassFileSource(info);
 	}
 
 	@Override
 	public String getLanguageName() {
 		return "java";
 	}
 
+	// -- Helper methods --
+
+	/**
+	 * Replacement for {@link LibraryInfo#getMainJreJarInfo()}, which is smarter
+	 * about Java 9+, and which does not spew messages to stderr.
+	 */
+	private static LibraryInfo getMainJreJarInfo() {
+		String javaHome = System.getProperty("java.home");
+		return getJreJarInfo(new File(javaHome));
+	}
+
+	/**
+	 * Replacement for {@link LibraryInfo#getJreJarInfo(java.io.File)}, which is
+	 * smarter about Java 9+, and which does not spew messages to stderr.
+	 */
+	private static LibraryInfo getJreJarInfo(final File jreHome) {
+		final File classesArchive = findExistingPath(jreHome, "lib/rt.jar",
+			"../Classes/classes.jar", "jmods/java.base.jmod");
+		if (classesArchive == null) return null; // unsupported JRE structure
+
+		final LibraryInfo info = new JarLibraryInfo(classesArchive);
+
+		final File sourcesArchive = findExistingPath(jreHome, "lib/src.zip",
+			"lib/src.jar", "src.zip", "../src.zip", "src.jar", "../src.jar");
+		if (sourcesArchive != null) {
+			info.setSourceLocation(new ZipSourceLocation(sourcesArchive));
+		}
+
+		return info;
+	}
+
+	private static File findExistingPath(final File baseDir, String... paths) {
+		for (final String path : paths) {
+			File file = new File(baseDir, path);
+			if (file.exists()) return file;
+		}
+		return null;
+	}
 }