Improve rendering outside request

Follow-up to [hotwired#529][]
Closes [hotwired#613][]

Add test coverage to ensure that rendering outside of a request does not
raise `nil`-related `NoMethodError`.

Alongside a change to replace the `#turbo_frame_request_id` method's `&`
operator with a conditional, this commit also makes a similar change to
the `#turbo_native_app?` method, since it accesses the user agent in a
similar way.

[hotwired#529]: hotwired#529
[hotwired#613]: hotwired#613

app/controllers/turbo/frames/frame_request.rb

@@ -33,6 +33,8 @@ def turbo_frame_request?
     end
 
     def turbo_frame_request_id
-      request&.headers["Turbo-Frame"]
+      if request
+        request.headers["Turbo-Frame"]
+      end
     end
 end

app/controllers/turbo/native/navigation.rb

@@ -12,7 +12,9 @@ module Turbo::Native::Navigation
 
   # Turbo Native applications are identified by having the string "Turbo Native" as part of their user agent.
   def turbo_native_app?
-    request.user_agent.to_s.match?(/Turbo Native/)
+    if request
+      request.user_agent.to_s.match?(/Turbo Native/)
+    end
   end
 
   # Tell the Turbo Native app to dismiss a modal (if presented) or pop a screen off of the navigation stack. Otherwise redirect to the given URL if Turbo Native is not present.

test/frames/frame_request_controller_test.rb

@@ -54,3 +54,22 @@ def with_prepended_view_path(path, &block)
       ApplicationController.view_paths = previous_view_paths
     end
 end
+
+class Turbo::FrameRequestViewTest < ActionView::TestCase
+  test "supports rendering context without request object" do
+    controller = ApplicationController.new
+    controller.request = nil
+
+    @rendered = controller.render_to_string(template: "trays/show")
+
+    assert_dom "html" do |html|
+      assert_dom html, "head" do |head|
+        assert_dom head, "title", text: "Dummy"
+        assert_dom head, "script"
+      end
+      assert_dom html, "body:not(.turbo-native)" do |body|
+        assert_dom body, "turbo-frame#tray"
+      end
+    end
+  end
+end