How to make breadcrumbs_on_rails render a Bootstrap compatible breadcrumb navigation

bootstrap_breadcrumbs_builder.rb

# The BootstrapBreadcrumbsBuilder is a Bootstrap compatible breadcrumb builder.
# It provides basic functionalities to render a breadcrumb navigation according to Bootstrap's conventions.
#
# BootstrapBreadcrumbsBuilder accepts a limited set of options:
# * separator: what should be displayed as a separator between elements
#
# You can use it with the :builder option on render_breadcrumbs:
#     <%= render_breadcrumbs :builder => ::BootstrapBreadcrumbsBuilder, :separator => "&raquo;" %>
#
# Note: You may need to adjust the autoload_paths in your config/application.rb file for rails to load this class:
#     config.autoload_paths += Dir["#{config.root}/lib/"]
#
class BootstrapBreadcrumbsBuilder < BreadcrumbsOnRails::Breadcrumbs::Builder
  def render
    @context.content_tag(:ul, class: 'breadcrumb') do
      @elements.collect do |element|
        render_element(element)
      end.join.html_safe
    end
  end

  def render_element(element)
    current = @context.current_page?(compute_path(element))

    @context.content_tag(:li, :class => ('active' if current)) do
      link_or_text = @context.link_to_unless_current(compute_name(element), compute_path(element), element.options)
      divider = @context.content_tag(:span, (@options[:separator]  || '/').html_safe, :class => 'divider') unless current

      link_or_text + (divider || '')
    end
  end
end

Updated for Bootstrap 4 (alpha6): https://gist.github.com/SaladFork/270a4cb3ac20be9715b7117551c31ec7

Of note:

• No longer has :separator option (Bootstrap 4 accomplishes this with CSS)
• Now has :container_tag option in addition to :tag option (default to :ol and :li, respectively)
• Now has :show_empty option which defaults to false to prevent rendering when there are no crumbs (h/t @mrfoto's fork)

Bootstrap 5

# The BootstrapBreadcrumbsBuilder is a Bootstrap compatible breadcrumb builder.
# It provides basic functionalities to render a breadcrumb navigation according to Bootstrap's conventions.
#
# You can use it with the :builder option on render_breadcrumbs:
#     <%= render_breadcrumbs :builder => ::BootstrapBreadcrumbsBuilder %>
#
# Note: you can put this file into app/utils/bootstrap_breadcrumbs_builder.rb and it will autoload.
#
class BootstrapBreadcrumbsBuilder < BreadcrumbsOnRails::Breadcrumbs::Builder
  def render
    @context.content_tag(:nav, 'aria-label' => "breadcrumb") do
      @context.content_tag(:ol, class: 'breadcrumb') do
        @elements.collect do |element|
          render_element(element)
        end.join.html_safe
      end
    end
  end

  def render_element(element)
    current = @context.current_page?(compute_path(element))

    classes = ['breadcrumb-item']
    classes.push('active') if current

    @context.content_tag(:li, :class => classes.join(" ") ) do
      link_or_text = @context.link_to_unless_current(compute_name(element), compute_path(element), element.options)
      link_or_text
    end
  end
end