Cannot access Rails view helpers methods when using with JBuilder

[vizcay]

According to documentation, gon supports JBuilder templates out of the box. In JBuilder, it is possible to use Rails view helpers methods without further configuration, but when trying to render them with gon.jbuilder it fails.

For example:

module ApplicationHelper
  def bigdecimal_to_cents(value)
    (value * 100).to_i if value
  end
end

undefined method `bigdecimal_to_cents' for #<Gon::Jbuilder::Parser:0x00007f943467f2f8>

Application Trace | Framework Trace | Full Trace
(eval):13:in `block (2 levels) in parse_source'
jbuilder (2.10.0) lib/jbuilder.rb:39:in `block in set!'
jbuilder (2.10.0) lib/jbuilder.rb:267:in `block in _merge_block'
jbuilder (2.10.0) lib/jbuilder.rb:306:in `_scope'
jbuilder (2.10.0) lib/jbuilder.rb:267:in `_merge_block'
jbuilder (2.10.0) lib/jbuilder.rb:39:in `set!'
jbuilder (2.10.0) lib/jbuilder/jbuilder_template.rb:100:in `set!'
jbuilder (2.10.0) lib/jbuilder.rb:67:in `method_missing'
(eval):1:in `block in parse_source'
gon (6.3.2) lib/gon/jbuilder/parser.rb:70:in `eval'
gon (6.3.2) lib/gon/jbuilder/parser.rb:70:in `block in parse_source'
jbuilder (2.10.0) lib/jbuilder.rb:19:in `initialize'
jbuilder (2.10.0) lib/jbuilder/jbuilder_template.rb:15:in `initialize'
jbuilder (2.10.0) lib/jbuilder.rb:24:in `new'
jbuilder (2.10.0) lib/jbuilder.rb:24:in `encode'
gon (6.3.2) lib/gon/jbuilder/parser.rb:69:in `parse_source'
gon (6.3.2) lib/gon/jbuilder/parser.rb:25:in `parse!'
gon (6.3.2) lib/gon/jbuilder.rb:18:in `handler'
gon (6.3.2) lib/gon.rb:96:in `jbuilder'
app/controllers/tiendas_controller.rb:11:in `tienda'
actionpack (6.0.2.2) lib/action_controller/metal/basic_implicit_render.rb:6:in `send_action'
actionpack (6.0.2.2) lib/abstract_controller/base.rb:196:in `process_action'
actionpack (6.0.2.2) lib/action_controller/metal/rendering.rb:30:in `process_action'
actionpack (6.0.2.2) lib/abstract_controller/callbacks.rb:42:in `block in process_action'
activesupport (6.0.2.2) lib/active_support/callbacks.rb:135:in `run_callbacks'
actionpack (6.0.2.2) lib/abstract_controller/callbacks.rb:41:in `process_action'
actionpack (6.0.2.2) lib/action_controller/metal/rescue.rb:22:in `process_action'
actionpack (6.0.2.2) lib/action_controller/metal/instrumentation.rb:33:in `block in process_action'
activesupport (6.0.2.2) lib/active_support/notifications.rb:180:in `block in instrument'
activesupport (6.0.2.2) lib/active_support/notifications/instrumenter.rb:24:in `instrument'
activesupport (6.0.2.2) lib/active_support/notifications.rb:180:in `instrument'
actionpack (6.0.2.2) lib/action_controller/metal/instrumentation.rb:32:in `process_action'
actionpack (6.0.2.2) lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
activerecord (6.0.2.2) lib/active_record/railties/controller_runtime.rb:27:in `process_action'
actionpack (6.0.2.2) lib/abstract_controller/base.rb:136:in `process'
actionview (6.0.2.2) lib/action_view/rendering.rb:39:in `process'
actionpack (6.0.2.2) lib/action_controller/metal.rb:191:in `dispatch'
actionpack (6.0.2.2) lib/action_controller/metal.rb:252:in `dispatch'
actionpack (6.0.2.2) lib/action_dispatch/routing/route_set.rb:51:in `dispatch'
actionpack (6.0.2.2) lib/action_dispatch/routing/route_set.rb:33:in `serve'
actionpack (6.0.2.2) lib/action_dispatch/journey/router.rb:49:in `block in serve'
actionpack (6.0.2.2) lib/action_dispatch/journey/router.rb:32:in `each'
actionpack (6.0.2.2) lib/action_dispatch/journey/router.rb:32:in `serve'
actionpack (6.0.2.2) lib/action_dispatch/routing/route_set.rb:837:in `call'
rack (2.2.2) lib/rack/tempfile_reaper.rb:15:in `call'
rack (2.2.2) lib/rack/etag.rb:27:in `call'
rack (2.2.2) lib/rack/conditional_get.rb:27:in `call'
rack (2.2.2) lib/rack/head.rb:12:in `call'
actionpack (6.0.2.2) lib/action_dispatch/http/content_security_policy.rb:18:in `call'
rack (2.2.2) lib/rack/session/abstract/id.rb:266:in `context'
rack (2.2.2) lib/rack/session/abstract/id.rb:260:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/cookies.rb:648:in `call'
activerecord (6.0.2.2) lib/active_record/migration.rb:567:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/callbacks.rb:27:in `block in call'
activesupport (6.0.2.2) lib/active_support/callbacks.rb:101:in `run_callbacks'
actionpack (6.0.2.2) lib/action_dispatch/middleware/callbacks.rb:26:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/actionable_exceptions.rb:17:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/debug_exceptions.rb:32:in `call'
web-console (4.0.1) lib/web_console/middleware.rb:132:in `call_app'
web-console (4.0.1) lib/web_console/middleware.rb:28:in `block in call'
web-console (4.0.1) lib/web_console/middleware.rb:17:in `catch'
web-console (4.0.1) lib/web_console/middleware.rb:17:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/show_exceptions.rb:33:in `call'
railties (6.0.2.2) lib/rails/rack/logger.rb:38:in `call_app'
railties (6.0.2.2) lib/rails/rack/logger.rb:26:in `block in call'
activesupport (6.0.2.2) lib/active_support/tagged_logging.rb:80:in `block in tagged'
activesupport (6.0.2.2) lib/active_support/tagged_logging.rb:28:in `tagged'
activesupport (6.0.2.2) lib/active_support/tagged_logging.rb:80:in `tagged'
railties (6.0.2.2) lib/rails/rack/logger.rb:26:in `call'
sprockets-rails (3.2.1) lib/sprockets/rails/quiet_assets.rb:13:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/remote_ip.rb:81:in `call'
request_store (1.5.0) lib/request_store/middleware.rb:19:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/request_id.rb:27:in `call'
rack (2.2.2) lib/rack/method_override.rb:24:in `call'
rack (2.2.2) lib/rack/runtime.rb:22:in `call'
activesupport (6.0.2.2) lib/active_support/cache/strategy/local_cache_middleware.rb:29:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/executor.rb:14:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/static.rb:126:in `call'
rack (2.2.2) lib/rack/sendfile.rb:110:in `call'
actionpack (6.0.2.2) lib/action_dispatch/middleware/host_authorization.rb:83:in `call'
webpacker (4.2.2) lib/webpacker/dev_server_proxy.rb:23:in `perform_request'
rack-proxy (0.6.5) lib/rack/proxy.rb:57:in `call'
railties (6.0.2.2) lib/rails/engine.rb:526:in `call'
puma (4.3.3) lib/puma/configuration.rb:228:in `call'
puma (4.3.3) lib/puma/server.rb:682:in `handle_request'
puma (4.3.3) lib/puma/server.rb:472:in `process_client'
puma (4.3.3) lib/puma/server.rb:328:in `block in run'
puma (4.3.3) lib/puma/thread_pool.rb:134:in `block in spawn_thread'

rails (6.0.2.2)
gon (6.3.2)
jbuilder (2.10.0)

[supairish]

I see this same behavior in a Rails 6.1.1 app