[Documentation] Form: document Rails form_with integration and real-world examples

[djalmaaraujo]

Closes #134

How to reproduce the gap

Open https://rubyui.com/docs/form — the existing docs show visual examples (disabled, error states, checkbox, select, combobox) but give no guidance on:

• How to set the form action / HTTP method
• What name / id to give each input so Rails params parse correctly
• How to wire a CSRF token
• How to map model.errors to FormFieldError

What changed

Three new items added immediately before the component-setup tabs in both gem/lib/ruby_ui/form/form_docs.rb and docs/app/views/docs/form.rb:

1. "Rails Integration" heading + prose — explains the recommended strategy: use form_with (or set action manually), set explicit name/id on every input, include the CSRF hidden field, and pass server-side errors via FormFieldError.
2. "Minimal Rails form" code example — a single-field form with action: helpers.users_path, CSRF token, FormFieldError, and a submit button; demonstrates the basic wiring.
3. "Devise-style login form" code example — a complete sign-in form using session[email] / session[password] / session[remember_me] params, autocomplete attributes, minlength validation, and error display — the real-world pattern most Rails devs need.

Testing instructions

• Visit /docs/form on a local or preview build and confirm the three new items appear below the Combobox example
• Verify the code blocks render correctly (no syntax highlighting errors)
• Copy the "Minimal Rails form" snippet into a Phlex view in a Rails app and confirm it submits with the correct params
• Copy the "Devise-style login form" snippet and confirm Devise recognises the session[email] / session[password] parameters

---

Summary by cubic

Adds a “Rails Integration” section to the Form docs with clear guidance on form_with, CSRF, input name/id, and mapping server errors to FormFieldError. Converts the Rails examples to code-only blocks so they don’t execute Rails helpers in the docs app.

• New Features

  • Prose on using form_with for action + CSRF, setting explicit name/id, and showing server errors with FormFieldError + model.errors.
  • Minimal Rails form example with a single email field, hidden CSRF input, and a submit button.
  • Devise-style login example using session[email], session[password], session[remember_me], with autocomplete, minlength, and error display.

• Bug Fixes

  • Render the two Rails examples as syntax-highlighted code via Heading + Codeblock (no instance_eval) to avoid crashes from missing helpers.* routes in the docs app; rebuilt mcp/data/registry.json.

^{Written for commit 55fd108. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

_{Re-trigger cubic}

[djalmaaraujo]

CI fixes applied

Failure 1 — Docs test crash (NoMethodError: undefined method 'users_path')

The two Rails-integration examples ("Minimal Rails form" and "Devise-style login form") in both docs/app/views/docs/form.rb and gem/lib/ruby_ui/form/form_docs.rb were wrapped in Docs::VisualCodeExample, which calls @context.instance_eval(code) to live-render a preview. The code referenced helpers.users_path and helpers.user_session_path which don't exist in the docs app, causing the controller test to crash.

Fix: Replaced both VisualCodeExample blocks with Heading(level: 3) + Codeblock(<<~RUBY, syntax: :ruby) — the same pattern used in docs/app/views/docs/data_table.rb. The code is now displayed as syntax-highlighted text only, never executed.

Failure 2 — MCP registry out of date

Re-ran cd mcp && bundle exec exe/ruby-ui-mcp-build, committed the updated mcp/data/registry.json.

Verified locally:

• gem: 225 tests, 992 assertions, 0 failures — StandardRB clean (366 files)
• docs: 63 tests, 63 assertions, 0 failures, 0 errors — StandardRB clean
• ruby -c on both changed view files: Syntax OK
• git diff --exit-code mcp/data/registry.json: clean after commit

[cirdes]

LGTM!