Linter Rule: Prefer the form_with helper over form_for

Rule: actionview-prefer-form-with

Description

Report calls to the form_for helper and point at form_with, which is the form builder Rails documents today.

fields_for is not part of this rule. It is the current API for nested attributes and is used together with form_with, so it is never reported.

Rationale

The Rails guides removed the form_for documentation and left a single closing section stating that form_tag and form_for are now discouraged in favor of form_with. The API docs still list form_for without a deprecation notice, there is no runtime deprecation warning, and no RuboCop cop covers it, so nothing in the toolchain tells you that a template is still on the Rails 5.0-era form API.

form_with covers everything form_for does. A record moves into model:, an as: option becomes scope:, and the html: hash flattens into top-level options.

<%= form_for @user, as: :customer, html: { class: "login" } do |form| %>
Prefer the `form_with` helper over `form_for`, which the Rails guides no longer document and describe as discouraged. Pass the record to `form_with` as `model:`, and move an `as:` option to `scope:` and `html:` options to the top level. (actionview-prefer-form-with)
  <%= form.text_field :name %>
<% end %>

becomes

<%= form_with model: @user, scope: :customer, class: "login" do |form| %>
  <%= form.text_field :name %>
<% end %>

The rule keys on a receiverless form_for call, so a helper of the same name called on an explicit receiver is left alone.

Examples

✅ Good

<%= form_with model: @user do |form| %>
  <%= form.text_field :name %>
<% end %>

<%= form_with model: [:admin, @user], scope: :customer do |form| %>
  <%= form.text_field :name %>
<% end %>

<%= form_with model: @user do |form| %>
  <%= form.fields_for :address do |address_form| %>
    <%= address_form.text_field :street %>
  <% end %>
<% end %>

🚫 Bad

<%= form_for @user do |form| %>
Prefer the `form_with` helper over `form_for`, which the Rails guides no longer document and describe as discouraged. Pass the record to `form_with` as `model:`, and move an `as:` option to `scope:` and `html:` options to the top level. (actionview-prefer-form-with)
  <%= form.text_field :name %>
<% end %>

<%= form_for [:admin, @user], as: :customer do |form| %>
Prefer the `form_with` helper over `form_for`, which the Rails guides no longer document and describe as discouraged. Pass the record to `form_with` as `model:`, and move an `as:` option to `scope:` and `html:` options to the top level. (actionview-prefer-form-with)
  <%= form.text_field :name %>
<% end %>

<%= form_for @user, url: session_path, html: { class: "login" } do |form| %>
Prefer the `form_with` helper over `form_for`, which the Rails guides no longer document and describe as discouraged. Pass the record to `form_with` as `model:`, and move an `as:` option to `scope:` and `html:` options to the top level. (actionview-prefer-form-with)
  <%= form.email_field :email %>
<% end %>

References

• Rails Guides: Form Helpers, "Using form_tag and form_for"
• ActionView::Helpers::FormHelper#form_for
• ActionView::Helpers::FormHelper#form_with