Simple Form 3 & Bootstrap 3

remove-this-sf_bs3_inputs.rb

#config/initializers/remove-this-sf_bs3_inputs.rb

#Credit: https://github.com/rafaelfranca/simple_form-bootstrap/issues/26#issuecomment-22435894

inputs = %w[
  CollectionSelectInput
  DateTimeInput
  FileInput
  GroupedCollectionSelectInput
  NumericInput
  PasswordInput
  RangeInput
  StringInput
  TextInput
]

inputs.each do |input_type|
  superclass = "SimpleForm::Inputs::#{input_type}".constantize

  new_class = Class.new(superclass) do
    def input_html_classes
      super.push('form-control')
    end
  end

  Object.const_set(input_type, new_class)
end

simple_form_bootstrap.rb

# Updated to bootstrap 3

SimpleForm.setup do |config|
  config.wrappers :bootstrap, tag: 'div', class: 'form-group', error_class: 'has-error' do |b|
    b.use :html5
    b.use :placeholder
    b.use :label
    b.use :input
    b.use :error, wrap_with: { tag: 'span', class: 'help-block' }
    b.use :hint,  wrap_with: { tag: 'p', class: 'help-block' }
  end

  config.wrappers :prepend, tag: 'div', class: "form-group", error_class: 'has-error' do |b|
    b.use :html5
    b.use :placeholder
    b.use :label
    b.wrapper tag: 'div', class: 'controls' do |input|
      input.wrapper tag: 'div', class: 'input-prepend' do |prepend|
        prepend.use :input
      end
      input.use :hint,  wrap_with: { tag: 'span', class: 'help-block' }
      input.use :error, wrap_with: { tag: 'span', class: 'help-block' }
    end
  end

  config.wrappers :append, tag: 'div', class: "form-group", error_class: 'has-error' do |b|
    b.use :html5
    b.use :placeholder
    b.use :label
    b.wrapper tag: 'div', class: 'controls' do |input|
      input.wrapper tag: 'div', class: 'input-append' do |append|
        append.use :input
      end
      input.use :hint,  wrap_with: { tag: 'span', class: 'help-block' }
      input.use :error, wrap_with: { tag: 'span', class: 'help-block' }
    end
  end

  # Wrappers for forms and inputs using the Twitter Bootstrap toolkit.
  # Check the Bootstrap docs (http://twitter.github.com/bootstrap)
  # to learn about the different styles for forms and inputs,
  # buttons and other elements.
  config.default_wrapper = :bootstrap
end

Do you have an example of how to use the prepend?

@bcackerman that's how I'm using prepend:

<%= f.input :email, wrapper: :prepend do %>
  <span class="input-group-addon"><i class="fa fa-envelope-o fa-fw"></i></span>
  <%= f.input_field :email, :autofocus => true %>
<% end %>