SmartFormBuilder

A Rails gem that extends ActionView::Helpers::FormBuilder with three automatic behaviours designed to eliminate boilerplate in view templates.

Features

1. Validation-reflected HTML attributes

Input, select, and textarea tags automatically receive HTML attributes derived from the model’s ActiveModel validators — no duplication between model and view:

Validator	HTML attribute added
validates :field, presence: true	required“required”= on inputs
validates :field, presence: true	class“required”= on the matching label
validates :field, length: { minimum }	minlength=N
validates :field, length: { maximum }	maxlength=N

Attributes that are already set explicitly in the view are never overwritten. Pass required: nil to suppress the automatic required attribute.

2. Inline field error rendering

A custom field_error_proc wraps each errored input in a .field_with_errors div and appends one .error_message span per error message. Labels are left unwrapped so they can be styled with the CSS :has() pseudo-class:

/* Style a label whose following sibling input has an error */
label:has(+ .field_with_errors) {
  color: red;
}

3. Base error block before the form

When the model passed to form_for / form_with has errors on :base, a #error_explanation div is rendered before the <form> tag automatically:

<div id="error_explanation">
  <ul>
    <li class="error">Something went wrong.</li>
  </ul>
</div>
<form ...>...</form>

No manual error block is needed in the view.

4. Disable-with on submit buttons

The FormBuilder#submit override auto-sets data-disable-with via I18n, using keys under helpers.disable_with.*:

# config/locales/en.yml
en:
  helpers:
    disable_with:
      create: "Creating %{model}..."
      update: "Saving %{model}..."

Model-specific keys are also supported:

en:
  helpers:
    disable_with:
      post:
        create: "Publishing %{model}..."

5. Nested model fieldsets

fields_for wraps nested model fields in a <fieldset> with the model’s DOM class and a new CSS class appended when the record is unsaved.

6. Group helper

f.group do … end wraps content in a <div class“group”>= — useful for grouping related fields inside a form.

Installation

Add to your Gemfile:

gem 'smart_form_builder'

Then run:

bundle install

No initializer is required. The Railtie wires everything up automatically via ActiveSupport.on_load hooks.

Usage

Because SmartFormBuilder::FormBuilder is set as the default form builder for all ActionController::Base subcontrollers, every form_for and form_with call in your application automatically uses it.

<%# All three features are active with no extra code in the view %>
<%= form_for @post do |f| %>
  <%= f.label :title %>
  <%= f.text_field :title %>   <%# required + maxlength inferred from validators %>

  <%= f.label :body %>
  <%= f.text_area :body %>

  <%= f.submit %>              <%# disable-with set automatically via I18n %>
<% end %>

CSS hooks

Selector	When it appears
#error_explanation li.error	errors[:base] is non-empty
.field_with_errors	Any field-level validation error
.field_with_errors span.error_message	Individual error message text
label.required	Field has a PresenceValidator

Customising the form builder

Inherit from SmartFormBuilder::FormBuilder instead of replacing it:

# app/helpers/application_helper.rb (or an initializer)
class MyFormBuilder < SmartFormBuilder::FormBuilder
  # add project-specific helpers here
end

# config/application.rb or an initializer:
config.action_view.default_form_builder = MyFormBuilder

Requirements

• Ruby >= 3.1
• Rails >= 7.0 (railties, actionview, activemodel)

License

MIT. See LICENSE.