heartcombo/simple_form · error · ArgumentError

A block is required as argument to wrapper

Error message

A block is required as argument to wrapper

What it means

Inside a config.wrappers block, b.wrapper(name, options) defines a nested group of components (a Wrappers::Many) built by yielding a fresh Builder to the block; the block is what populates the group, so calling b.wrapper without one raises ArgumentError rather than registering an empty wrapper (lib/simple_form/wrappers/builder.rb:71). Single components are added with b.use / b.optional instead.

Source

Thrown at lib/simple_form/wrappers/builder.rb:71

          @components << Leaf.new(name, options)
        end
      end

      def optional(name, options = {}, &block)
        @options[name] = false
        use(name, options)
      end

      def wrapper(name, options = nil)
        if block_given?
          name, options = nil, name if name.is_a?(Hash)
          builder = self.class.new(@options)
          options ||= {}
          options[:tag] = :div if options[:tag].nil?
          yield builder
          @components << Many.new(name, builder.to_a, options)
        else
          raise ArgumentError, "A block is required as argument to wrapper"
        end
      end

      def to_a
        @components
      end
    end
  end
end

View on GitHub (pinned to 18f38aad0b)

Solutions

1. Supply a block: b.wrapper :addons do |w| w.use :prefix; w.use :input; w.use :suffix end
2. If you only wanted a single component, use b.use :input (or b.optional :pattern) instead of b.wrapper
3. Restart the app after fixing the initializer so the corrected wrappers are re-registered

Example fix

# before
SimpleForm.setup do |config|
  config.wrappers :default do |b|
    b.wrapper :addons   # ArgumentError: block required
  end
end

# after
SimpleForm.setup do |config|
  config.wrappers :default do |b|
    b.wrapper :addons do |w|
      w.use :prefix
      w.use :input
      w.use :suffix
    end
  end
end

begin
  require Rails.root.join('config/initializers/simple_form')
rescue ArgumentError => e
  abort "Fix config/initializers/simple_form.rb (missing block in b.wrapper?): #{e.message}"
end

When it happens

Trigger: config.wrappers :default do |b| b.wrapper :addons end (missing do...end); passing components as extra positional args (b.wrapper :addons, :input); confusing b.wrapper (nested group, block required) with b.use (single leaf component).

Common situations: Hand-editing a long initializer and losing the do...end; merge conflicts in wrapper config; learning the wrapper DSL and mixing up use and wrapper.

Related errors

• You need to give :to as option to map_type
• Couldn't find wrapper with name #{name}
• Association cannot be used in forms not associated with an o
• :has_one associations are not supported by f.association
• SimpleForm.include_component expects a module but got: #{com

AI-assisted analysis of heartcombo/simple_form@18f38aad0b (2026-08-21). Data as JSON: /api/errors/48e29ab821869b74. Report an issue: GitHub.