Bug 6672 jar no longer exported after attach source
1206 1. Create a project test. 2. Add a jar (say resources.jar) to the classpath and export the entry 3. Attach source (say resourcessrc.zip) to the jar. Notice, the jar is no longer exported - this information is discarded during the attach source process.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/SourceAttachmentBlock.java
if (fIsVariableEntry) {
				
				return fPrefixStatus.isOK() && fPrefixField.getText().length() > 0;
			}
			return true;
		}
		return false;
	}	
	
	private String getResolvedLabelString(String path, boolean osPath) {
		IPath resolvedPath= getResolvedPath(new Path(path));
		if (resolvedPath != null) {
			if (osPath) {
				return resolvedPath.toOSString();
			} else {
				return resolvedPath.toString();
			}
		}
		return ""; 
	}	
	
	private IPath getResolvedPath(IPath path) {
		if (path != null) {
			String varName= path.segment(0);
			if (varName != null) {
				IPath varPath= JavaCore.getClasspathVariable(varName);
				if (varPath != null) {
					return varPath.append(path.removeFirstSegments(1));
				}
			}