Show source view and backtrace on missing template errors

This will help you debug missing template errors, especially if they
come from a programmatic template selection. Thanks to @dhh for
suggesting that.

As a bonus, also show request and response info on the routing error
page for consistency.

actionpack/lib/action_dispatch/middleware/templates/rescues/missing_template.html.erb

@@ -4,4 +4,8 @@
 
 <div id="container">
   <h2><%= h @exception.message %></h2>
+
+  <%= render template: "rescues/_source" %>
+  <%= render template: "rescues/_trace" %>
+  <%= render template: "rescues/_request_and_response" %>
 </div>

actionpack/lib/action_dispatch/middleware/templates/rescues/routing_error.html.erb

@@ -27,4 +27,6 @@
 
     <%= @routes_inspector.format(ActionDispatch::Routing::HtmlTableFormatter.new(self)) %>
   <% end %>
+
+  <%= render template: "rescues/_request_and_response" %>
 </div>

actionpack/test/dispatch/debug_exceptions_test.rb

@@ -43,6 +43,8 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
         raise ActionController::InvalidAuthenticityToken
       when "/not_found_original_exception"
         raise ActionView::Template::Error.new('template', AbstractController::ActionNotFound.new)
+      when "/missing_template"
+        raise ActionView::MissingTemplate.new(%w(foo), 'foo/index', %w(foo), false, 'mailer')
       when "/bad_request"
         raise ActionController::BadRequest
       when "/missing_keys"
@@ -120,6 +122,15 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
     assert_no_match '&lt;|&gt;', routing_table, "there should not be escaped html in the output"
   end
 
+  test 'displays request and response info when a RoutingError occurs' do
+    @app = DevelopmentApp
+
+    get "/pass", {}, {'action_dispatch.show_exceptions' => true}
+
+    assert_select 'h2', /Request/
+    assert_select 'h2', /Response/
+  end
+
   test "rescue with diagnostics message" do
     @app = DevelopmentApp
 
@@ -275,6 +286,22 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
     end
   end
 
+  test 'display backtrace on template missing errors' do
+    @app = DevelopmentApp
+
+    get "/missing_template", nil, {}
+
+    assert_select "header h1", /Template is missing/
+
+    assert_select "#container h2", /^Missing template/
+
+    assert_select '#Application-Trace'
+    assert_select '#Framework-Trace'
+    assert_select '#Full-Trace'
+
+    assert_select 'h2', /Request/
+  end
+
   test 'display backtrace when error type is SyntaxError wrapped by ActionView::Template::Error' do
     @app = DevelopmentApp