Render inline errors in Rails forms after submit and hotwire changes

_form.html.erb

<%= form_for customer, html: { id: dom_id(customer), class: 'row g-3' } do |f| %>
<% presenter = InlineErrorRenderer.new(customer, self, 'form-control-lg form-control-solid mb-3 mb-lg-0') %>
  <div class='col-md-6'>
    <%= f.label :full_name %>
    <%= f.text_field :full_name, presenter.html_options_for(:full_name) %>
    <%= presenter.error_container_for(:full_name) %>
  </div>
  <div class='col-md-6'>
    <%= f.label :phone_number, 'Phone Number' %>
    <%= f.text_field :phone_number, presenter.html_options_for(:phone_number) %>
    <%= presenter.error_container_for(:phone_number) %>
  </div>
  <div class='col-md-6'>
    <%= f.label :email, 'Email' %>
    <%= f.text_field :email, presenter.html_options_for(:email) %>
    <%= presenter.error_container_for(:email) %>
  </div>
  <div class="col-md-6">
     <%= f.label :country, 'Country' %>
     <%= country_select(f, "country", { priority_countries: ['IN', 'US'], selected: "IN" }, presenter.html_options_for(:country)) %>
     <%= presenter.error_container_for(:country) %>
  </div>
  <div class="col-12">
    <%= f.submit 'Submit', class: 'btn btn-outline-secondary' %>
    <%= link_to 'Back', customers_path, class: 'btn btn-outline-warning' %>
  </div>
<% end %>

errors.scss

// Rails forms when in error state wraps each form element inside div with "field_with_errors" class.
// Therefore bootstrap error classes (invalid-feedback, is-invalid) won't work because of following structure.

// <div class="form-control">
//   <div class="field_with_errors">
//     <input type="text" class="is-invalid"
//   </div>
// </div>

.invalid-feedback {
  display: block !important;
}

.form-control.form-control-solid.is-invalid {
  border-color: #F1416C;
}

hotwire_changes.rb

# This is optional but if you want to use hotwire then just return the error response in turbo_stream in controller

def create
  @customer.user_id = current_user.id
  respond_to do |format|
    if @customer.save
      # do usual stuff
    else
      format.turbo_stream
    end
  end
end

# and handle that turbo_stream response in create.turbo_stream.erb
<%= turbo_stream.replace "new_customer", partial: "customers/form", locals: { customer: @customer } %>

inline_error_renderer.rb

# InlineErrorRenderer is based on TwitterBootstrap's server side form validations.
# https://getbootstrap.com/docs/5.0/forms/validation/#server-side

class InlineErrorRenderer
  def initialize(model, template, default_classes)
    @model = model
    @template = template
    @default_classes = default_classes
  end

  FORM_INVALID = '%s %s is-invalid'
  ARIA = '%s_aria'

  def html_options_for(attr, html_class = nil)
    if errors[attr].present?
      {
        class: format(FORM_INVALID, default_classes, html_class),
        aria: { describedby: format(ARIA, attr) }
      }
    else
      { class: default_classes }
    end
  end

  def error_container_for(attr)
    if errors[attr].present?
      template.tag.div(class: 'invalid-feedback', id: format(ARIA, attr)) do
        errors[attr].join(',').html_safe
      end
    end
  end

  private
  attr_reader :model, :template, :default_classes

  def errors
    @errors ||= model.errors
  end
end