Move preview controllers to the engine

[camertron]

What are you trying to accomplish?

Hey everyone 👋 I'm contracting with the OpenProject team for the next few weeks on a couple of new Primer components they need for their app. The OP team mounts all Primer's component previews inside their app's Lookbook, much like GitHub does inside dotcom's Lookbook. Several of PVC's previews however rely on server-side behavior in controllers and views that live in the demo app, eg. demo/app/controllers and demo/app/views. This means that, while some previews render just fine in OP's Lookbook, some error out or simply don't work.

This PR addresses the issue by moving these controllers and views into PVC's Rails engine. This makes them accessible to a host application via Rails' engine mounting mechanism. In other words, a host app can make everything Just Work™ by adding the following to the app's config/routes.rb:

mount Primer::ViewComponents::Engine, at: "/" # or whatever path you want

I have verified everything works as expected inside OpenProject's app. This change should not affect dotcom or any other GitHub property, as the functionality in question is dev-only (or at least, not user-facing) and maintains all existing functionality.

Can't stop, won't stop!

Integration

No changes necessary in production.

Risk Assessment

• Low risk the change is small, highly observable, and easily rolled back.
• Medium risk changes that are isolated, reduced in scope or could impact few users. The change will not impact library availability.
• High risk changes are those that could impact customers and SLOs, low or no test coverage, low observability, or slow to rollback.

Accessibility

• No new axe scan violation - This change does not introduce any new axe scan violations.

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Lookbook)
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge

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[Copilot]

Pull Request Overview

Moves server-side preview controllers and views into the Primer::ViewComponents Rails engine and updates form helper paths to point at the new engine routes.

• Updates ImmediateValidationForm to use engine routes for auto-check endpoints
• Adds a suite of preview controllers under app/controllers/primer/view_components
• Introduces an engine-level ApplicationController for all preview controllers

Reviewed Changes

Copilot reviewed 69 out of 69 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
app/forms/immediate_validation_form.rb	Updated auto_check_src to use engine route helpers
app/controllers/primer/view_components/application_controller.rb	New base controller for engine previews
app/controllers/primer/view_components/toggle_switch_controller.rb	Added preview controller for toggle switch
app/controllers/primer/view_components/select_panel_items_controller.rb	Added preview controller for select panel items
app/controllers/primer/view_components/nav_list_items_controller.rb	Added preview controller for nav list pagination
app/controllers/primer/view_components/multi_controller.rb	Added preview controller for multi-input form
app/controllers/primer/view_components/include_fragment_controller.rb	Added preview controller for fragment inclusion
app/controllers/primer/view_components/form_handler_controller.rb	Added preview controller for form submission demo
app/controllers/primer/view_components/auto_complete_test_controller.rb	Added preview controller for autocomplete behavior
app/controllers/primer/view_components/auto_check_controller.rb	Added preview controller for auto-check behaviors
app/controllers/primer/view_components/action_menu_controller.rb	Added preview controller for action menu demos

Comments suppressed due to low confidence (2)

app/controllers/primer/view_components/select_panel_items_controller.rb:21

• The page offset calculation is incorrect. For page 1 it yields -2. It should likely be (params[:page].to_i - 1) * items_per_page.

start_index = (params[:page].to_i - items_per_page) * items_per_page

app/controllers/primer/view_components/toggle_switch_controller.rb:1

• Consider adding a basic request spec to verify the create endpoint returns the correct status and handles the fail parameter.

# frozen_string_literal: true

[jonrohan]

Thanks @camertron There's a failure still going on, something about a missing method in the forms previews?

[camertron]

@jonrohan whoops, should be fixed now 😄

[camertron]

@jonrohan oops, looks like there was one more URL helper that needed to be fixed. Should be good now.

Feel like adding me to the list of users allowed to kick off workflow runs? 😉