Bug 8808 Class folder: Must use create to add an existing folder
Build I20020129 "Add Folders..." does not show the project itself. I have to do the following trick to add an existing folder as class folder: Press "Create folder" Enter the name of the existing folder (hopfully it's in the project root :-) Voila BTW: I can't do this a second time - the UI tells me it already exists - which is OK. To be consistent with other dialogs "Create Folder" should always warn about existing projects.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/LibrariesWorkbookPage.java
public SourceAttachmentDialog(Shell parent, IClasspathEntry entry) {
			super(parent);
			setTitle(NewWizardMessages.getFormattedString("LibrariesWorkbookPage.SourceAttachmentDialog.title", entry.getPath().toString())); 
			fSourceAttachmentBlock= new SourceAttachmentBlock(fWorkspaceRoot, this, entry);
		}
		
		/*
		 * @see Windows#configureShell
		 */
		protected void configureShell(Shell newShell) {
			super.configureShell(newShell);
			WorkbenchHelp.setHelp(newShell, IJavaHelpContextIds.SOURCE_ATTACHMENT_DIALOG);
		}		
				
		protected Control createDialogArea(Composite parent) {
			Composite composite= (Composite)super.createDialogArea(parent);
						
			Control inner= fSourceAttachmentBlock.createControl(composite);
			inner.setLayoutData(new GridData(GridData.FILL_BOTH));
			return composite;
		}
		
		public void statusChanged(IStatus status) {
			updateStatus(status);
		}
		
		public IPath getSourceAttachmentPath() {
			return fSourceAttachmentBlock.getSourceAttachmentPath();
		}