Bug 9159 Classpath wizard should not complain when adding missing source folder
Build 20020125 - Define a project A with source folder 'src1'. - Go to the .classpath file and edit it to insert one extra line: <classpathentry kind="src" path="src2"/> below the line referring to first source folder: <classpathentry kind="src" path="src1"/>. - Now, try to add this missing source folder 'src2', it isn't allowed by the wizard, one has to add a basic folder instead. Note: It is not such an uncommon scenario, the classpath modification could simply occur by catching up with a shared classpath having one more source folder on it, and which is locally missing.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/BuildPathsBlock.java
private List getDefaultClassPath(IJavaProject jproj) {
		List list= new ArrayList();
		IResource srcFolder;
		if (JavaBasePreferencePage.useSrcAndBinFolders()) {
			String sourceFolderName= JavaBasePreferencePage.getSourceFolderName();
			srcFolder= jproj.getProject().getFolder(sourceFolderName);
		} else {
			srcFolder= jproj.getProject();
		}
		list.add(new CPListElement(IClasspathEntry.CPE_SOURCE, srcFolder.getFullPath(), srcFolder));
		IPath libPath= new Path(JavaRuntime.JRELIB_VARIABLE);
		IPath attachPath= new Path(JavaRuntime.JRESRC_VARIABLE);
		IPath attachRoot= new Path(JavaRuntime.JRESRCROOT_VARIABLE);
		CPListElement elem= new CPListElement(IClasspathEntry.CPE_VARIABLE, libPath, null, attachPath, attachRoot, false);
		list.add(elem);
		return list;
	}
	
	private IPath getDefaultBuildPath(IJavaProject jproj) {
		if (JavaBasePreferencePage.useSrcAndBinFolders()) {
			String outputLocationName= JavaBasePreferencePage.getOutputLocationName();
			return jproj.getProject().getFullPath().append(outputLocationName);
		} else {
			return jproj.getProject().getFullPath();
		}
	}	
		
	private class BuildPathAdapter implements IStringButtonAdapter, IDialogFieldListener {