Navigation link helper
Returns an `li` element with an ‘active’ class if the supplied
controller(s) and/or action(s) are currently active. The content of the
element is the value passed to the block.
options - The options hash used to determine if the element is “active”
(default: {})
:controller   - One or more controller names to check (optional).
:action       - One or more action names to check (optional).
:path         - A shorthand path, such as 'dashboard#index', to check (optional).
:html_options - Extra options to be passed to the list element (optional).
block   - An optional block that will become the contents of the returned
`li` element.
When both :controller and :action are specified, BOTH must match in order
to be marked as active. When only one is given, either can match.
Examples
nav_link(controller: [:tree, :refs], action: :edit) { "Hello" }
nav_link(controller: [:tree, :refs]) { "Hello" }
nav_link(path: 'tree#show') { "Hello" }
nav_link(controller: :tree, html_options: {class: 'home'}) { "Hello" }
Returns a list item element String
          
          
          
            
def nav_link(options = {}, &block)
  if path = options.delete(:path)
    c, a, _ = path.split('#')
  else
    c = options.delete(:controller)
    a = options.delete(:action)
  end
  if c && a
    
    klass = current_controller?(*c) && current_action?(*a) ? 'active' : ''
  else
    
    klass = current_controller?(*c) || current_action?(*a) ? 'active' : ''
  end
  
  
  o = options.delete(:html_options) || {}
  o[:class] ||= ''
  o[:class] += ' ' + klass
  o[:class].strip!
  if block_given?
    content_tag(:li, capture(&block), o)
  else
    content_tag(:li, nil, o)
  end
end