_trace.erb

# app/views/rescues/_trace.erb

<%
  traces = [
    ["Application Trace", @exception.application_backtrace],
    ["Framework Trace", @exception.framework_backtrace],
    ["Full Trace", @exception.clean_backtrace]
  ]
  names = traces.collect {|name, trace| name}
%>

<p><code>RAILS_ROOT: <%= defined?(RAILS_ROOT) ? RAILS_ROOT : "unset" %></code></p>

<div id="traces">
  <% names.each do |name| %>
    <%
      show = "document.getElementById('#{name.gsub /\s/, '-'}').style.display='block';"
      hide = (names - [name]).collect {|hide_name| "document.getElementById('#{hide_name.gsub /\s/, '-'}').style.display='none';"}
    %>
    <a href="#" onclick="<%= hide.join %><%= show %>; return false;"><%= name %></a> <%= '|' unless names.last == name %>
  <% end %>

  <% traces.each do |name, trace| %>
    <div id="<%= name.gsub /\s/, '-' %>" style="display: <%= name == "Application Trace" ? 'block' : 'none' %>;">
<%
  # Original code was:
  # <pre><code><%=h trace.join "\n" %></code></pre>
%>

      <pre><code><%= raw trace.join "<br/>\n" %></code></pre>
    </div>
  <% end %>
</div>

application_controller.rb

# app/controllers/application_controller.rb

#
# ALTERNATIVELY TO THE INITIALIZER BELOW, THIS WILL LET YOU DEBUG THE TEMPLATES
# AS IT WILL RELOAD WITH EACH REQUEST IN DEVELOPMENT
#

class ApplicationController < ActionController::Base

  # Render detailed diagnostics for unhandled exceptions rescued from
  # a controller action.
  def rescue_action_locally(exception)
    class << RESCUES_TEMPLATE_PATH
      def [](path)
        if Rails.root.join("app/views", path).exist?
          ActionView::Template::EagerPath.new_and_loaded(Rails.root.join("app/views").to_s)[path]
        else
          super
        end
      end
    end
    super
  end

end

clickable_stacktrace.rb

# config/initializers/clickable_stacktrace.rb

#
# TO LOAD FUNCTIONALITY IN AN INITIALIZER
# 

module ActionController
  module Rescue
    class << RESCUES_TEMPLATE_PATH
      def [](path)
        if Rails.root.join("app/views", path).exist?
          ActionView::Template::EagerPath.new_and_loaded(Rails.root.join("app/views").to_s)[path]
        else
          super
        end
      end
    end
  end
end