form_builder.rb

class ApplicationFormBuilder < ActionView::Helpers::FormBuilder
  def form_group(method, options = {}, &block)
    content = @template.capture(&block)
    content += help_block_with_errors(method) if object.errors[method].any?

    options[:class] ||= ''
    options[:class] += ' form-group'
    options[:class] += ' has-error' if object.errors[method].any?

    @template.content_tag :div, content, options
  end

  def label(method, text = nil, options = {}, &block)
    text ||= @template.t(".#{method}.label")

    options[:class] ||= ''
    options[:class] += ' control-label'

    super(method, text, options, &block)
  end

  %w(text_field number_field date_field email_field password_field text_area).each do |field_helper|
    define_method field_helper do |method, options = {}|
      options[:class] ||= ''
      options[:class] += ' form-control'

      options[:placeholder] ||= @template.t(".#{method}.placeholder", default: '')

      super(method, options)
    end
  end

  def submit(value = nil, options = {})
    unless value.is_a? String
      options = value
      value = @template.t('.submit')
    end

    super(value, options)
  end

  private

  def help_block_with_errors(method)
    @template.content_tag(
      :span, object.errors[method].join(', '), class: 'help-block has-error'
    )
  end
end


# Disable .field_with_errors wrapper for invalid forms
ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
  html_tag.html_safe
end

ActionView::Base.default_form_builder = 'ApplicationFormBuilder'