Conditionally generate assets during setup

Clobber and precompile assets during setup if using [Sprockets][]. This
is helpful in cases where one might switch branches frequently, which
can result in broken assets.

[Sprockets]: https://github.com/rails/sprockets

lib/generators/templates/setup/bin_setup.rb

@@ -43,6 +43,11 @@ def using_node?
   puts "\n== Preparing database and adding development seed data =="
   system! "bin/rails dev:prime"
 
+  if Rake::Task.task_defined?("assets:clobber") && Rake::Task.task_defined("assets:precompile")
+    puts "\n== Generating assets =="
+    system! "bin/rails assets:clobber assets:precompile"
+  end
+
   # https://github.com/rails/rails/pull/47719/files
   puts "\n== Setup test environment =="
   system! "bin/rails test:prepare"