Solution 1:

You need a + to quick fix :D

module InputHelper
  def editable_input(label,name)
    content_tag :div, :class => "field" do
      content_tag(:label,label) + # Note the + in this line
      text_field_tag(name,'', :class => 'medium new_value')
    end
  end
end

<%= editable_input 'Year Founded', 'companyStartDate' %>

Inside the block of content_tag :div, only the last returned string would be displayed.

Solution 2:

You can also use the concat method:

module InputHelper
  def editable_input(label,name)
    content_tag :div, :class => "field" do
      concat(content_tag(:label,label))
      concat(text_field_tag(name,'', :class => 'medium new_value'))
    end
  end
end

Source: Nesting content_tag in Rails 3

Solution 3:

I use a variable and concat to help with deeper nesting.

def billing_address customer
  state_line = content_tag :div do
    concat(
      content_tag(:span, customer.BillAddress_City) + ' ' +
      content_tag(:span, customer.BillAddress_State) + ' ' +
      content_tag(:span, customer.BillAddress_PostalCode)
    )
  end
  content_tag :div do
    concat(
      content_tag(:div, customer.BillAddress_Addr1) +
      content_tag(:div, customer.BillAddress_Addr2) +
      content_tag(:div, customer.BillAddress_Addr3) +
      content_tag(:div, customer.BillAddress_Addr4) +
      content_tag(:div, state_line) +
      content_tag(:div, customer.BillAddress_Country) +
      content_tag(:div, customer.BillAddress_Note)
    )
  end
end

Solution 4:

building nested content tags with iteration is a little different and gets me every time... here is one method:

      content_tag :div do
        friends.pluck(:firstname).map do |first| 
          concat( content_tag(:div, first, class: 'first') )
        end
      end