padrino/padrino-framework · error

gem 'padrino-helpers' is required to render partials

Error message

gem 'padrino-helpers' is required to render partials

What it means

padrino-mailer's Ext module redefines partial by aliasing the pre-existing implementation as original_partial; that implementation only exists when padrino-helpers was loaded first. The guard respond_to?(:original_partial) fails when padrino-helpers is absent, so calling partial inside a mail template raises this error pointing at the missing gem.

Source

Thrown at padrino-mailer/lib/padrino-mailer/ext.rb:284

      if mailer_name && !engine.to_s.index('/')
        settings.views += "/#{mailer_name}" unless settings.views.include?("/#{mailer_name}")
        engine = engine.to_s.sub(%r{^#{mailer_name}/}, '')
      end

      provides.each do |format|
        part do |p|
          p.content_type(format)
          p.send(:render, engine, data, options, locals, &block)
          add_multipart_alternate_header if html_part || provides.include?(:html)
        end
      end

      self.body = super(engine, data, options, locals, &block) if provides.empty?
    end

    alias original_partial partial if instance_methods.include?(:partial)
    def partial(template, options = {}, &block)
      raise "gem 'padrino-helpers' is required to render partials" unless respond_to?(:original_partial)
      self.body = original_partial(template, options, &block)
    end

    ##
    # Register all special template configurations Padrino has to our fake settings object.
    #
    def initialize_template_settings!
      Padrino::Rendering.engine_configurations.each do |name, value|
        settings.class.instance_eval { define_method(name) { value } }
      end
    end
  end
end

View on GitHub (pinned to 167044f3d5)

Solutions

1. Add gem 'padrino-helpers' to the Gemfile (same version constraint as padrino-mailer) and run bundle install
2. If the gem is present but the error persists, require 'padrino-helpers' explicitly in boot.rb so it loads before mailer templates render
3. If you intentionally ship without padrino-helpers, replace partial calls in mail templates with inline markup or full-path render calls

Example fix

# before — Gemfile
gem 'padrino-mailer'

# after — Gemfile
gem 'padrino-mailer'
gem 'padrino-helpers'

# fail at boot instead of at the first mail render
unless defined?(Padrino::Helpers) || Gem.loaded_specs['padrino-helpers']
  abort 'add gem "padrino-helpers" to render partials inside mailers'
end

When it happens

Trigger: Calling partial 'user_row' inside a mailer view when the Gemfile contains padrino-mailer but not padrino-helpers; using padrino-mailer standalone with a Sinatra app without the helpers gem; upgrading an app whose partials worked before helpers were extracted.

Common situations: Upgrading Padrino 0.13 to 0.14 or later, where rendering helpers moved into the separate padrino-helpers gem; minimal custom stacks that include only the mailer; Sinatra apps adopting padrino-mailer just for its DSL.

Related errors

• Engine #{engine.inspect} is not registered with Tilt
• The email '#{name}' is already defined
• mailer '#{mailer_name}' is not registered
• mailer '#{mailer_name}' has no message '#{message_name}'
• To use mailers on Windows you must set a :delivery_method, s

AI-assisted analysis of padrino/padrino-framework@167044f3d5 (2026-08-23). Data as JSON: /api/errors/09d9cc30f1c85a17. Report an issue: GitHub.