Handle exceptions during TURBO_STREAM requests

app/controllers/application_controller.rb

@@ -3,8 +3,19 @@ class ApplicationController < ActionController::Base
 
   before_action :authenticate_user!
 
-  class AccessForbidden < StandardError
-  end
+  class AccessForbidden < StandardError; end
+  class ParameterInvalid < StandardError; end
+
+  # Exceptions are handled depending on request format:
+  # * HTML is handled by PublicExceptions, resulting in display of
+  #   'public/<status-code>.html' template.
+  # * TURBO_STREAM is handled by method specified below, which writes flash
+  #   message and forces redirect to referer - to display flash and make page
+  #   content consistent with database (which may or may not have been
+  #   modified before exception).
+  #   This requires referer to be available in TURBO_STREAM format. Otherwise
+  #   Turbo will reload 2nd time with HTML format and flashes will be lost.
+  rescue_from *ActionDispatch::ExceptionWrapper.rescue_responses.keys, with: :rescue_turbo
 
   protected
 
@@ -23,4 +34,14 @@ class ApplicationController < ActionController::Base
   def after_sign_out_path_for(scope)
     new_user_session_path
   end
+
+  private
+
+  def rescue_turbo(exception)
+    raise unless request.format.to_sym == :turbo_stream
+
+    message_id = ActionDispatch::ExceptionWrapper.rescue_responses[exception.class.to_s]
+    flash.alert = t("actioncontroller.exceptions.status.#{message_id}")
+    redirect_to request.referer
+  end
 end