acts_as_taggable_on + simple_form + select2

app__assets__tags_input.coffee

$(document).on 'ready page:load', ->
  $('select.form-control.tags').select2({tags: true});

app__inputs__tags_input.rb

class TagsInput < SimpleForm::Inputs::CollectionInput
  enable :placeholder

  def input(wrapper_options = {})
    @collection ||= @builder.object.send(attribute_name)
    label_method, value_method = detect_collection_methods

    merged_input_options = merge_wrapper_options(input_html_options, wrapper_options)
    merged_input_options.reverse_merge!(multiple: true)

    @builder.collection_select(
      attribute_name, collection, value_method, label_method,
      input_options, merged_input_options
    )
  end
end

brabra

# in application.coffee
#= require select2

# in application.scss
*= require select2
*= require select2-bootstrap

# in controller
permit(tag_list: [])

form.html.haml

    = f.input :tag_list, as: :tags

Gemfile

gem 'acts-as-taggable-on'
gem 'simple_form'
gem 'select2-rails'

Thank you . This is perfect