Bug 123786 Following bug 109980, the compliance 6.0 should be added to the compiler's compliance list.
If the JRE/JDK used is a 1.6/6.0 VM, then the compliance 6.0 should be available. Compliance 1.6 implies source level 1.6 and target level 1.6.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/ComplianceConfigurationBlock.java
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.events.SelectionListener;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Combo;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Group;
import org.eclipse.swt.widgets.Link;
import org.eclipse.jface.dialogs.ControlEnableState;
import org.eclipse.ui.dialogs.PreferencesUtil;
import org.eclipse.ui.preferences.IWorkbenchPreferenceContainer;
import org.eclipse.jdt.core.JavaCore;
import org.eclipse.jdt.launching.IVMInstall;
import org.eclipse.jdt.launching.JavaRuntime;
import org.eclipse.jdt.internal.ui.JavaPlugin;
import org.eclipse.jdt.internal.ui.dialogs.StatusInfo;
import org.eclipse.jdt.internal.ui.util.PixelConverter;
import org.eclipse.jdt.internal.ui.wizards.IStatusChangeListener;
import org.eclipse.jdt.internal.ui.wizards.buildpaths.BuildPathSupport;
/**
  */
public class ComplianceConfigurationBlock extends OptionsConfigurationBlock {
	
	private static final Key PREF_LOCAL_VARIABLE_ATTR=  getJDTCoreKey(JavaCore.COMPILER_LOCAL_VARIABLE_ATTR);
	private static final Key PREF_LINE_NUMBER_ATTR= getJDTCoreKey(JavaCore.COMPILER_LINE_NUMBER_ATTR);
	private static final Key PREF_SOURCE_FILE_ATTR= getJDTCoreKey(JavaCore.COMPILER_SOURCE_FILE_ATTR);
	private static final Key PREF_CODEGEN_UNUSED_LOCAL= getJDTCoreKey(JavaCore.COMPILER_CODEGEN_UNUSED_LOCAL);
	private static final Key PREF_CODEGEN_TARGET_PLATFORM= getJDTCoreKey(JavaCore.COMPILER_CODEGEN_TARGET_PLATFORM);