feat(views): replace chapters sidebar with ViewComponent

[mroderick]

Summary

• Replaces the inline HAML chapters sidebar on the homepage with a reusable ViewComponent
• Uses Rails fragment caching (cache "chapters-sidebar") for performance
• Adds cache expiration callbacks to Chapter model (after_create_commit, after_update_commit, after_destroy_commit)
• Adds component specs for the ViewComponent
• Adds view specs for the dashboard show page
• Adds cache expiration tests to chapter_spec.rb
• Fixes broken use_transactional_fixtures check in spec_helper.rb

Caching Strategy

How it works

The component uses Rails fragment caching to cache the rendered HTML for the chapters sidebar:

<% cache "chapters-sidebar" do %>
  <!-- rendered HTML is cached -->
<% end %>

This caches the entire sidebar HTML fragment under the key "chapters-sidebar". On subsequent requests, Rails serves the cached fragment directly from the cache store (typically Redis in production), bypassing view rendering entirely.

Cache Invalidation

The cache is automatically invalidated when Chapters are created, updated, or deleted via Active Record callbacks in Chapter model:

after_update_commit :expire_chapters_sidebar_cache
after_create_commit :expire_chapters_sidebar_cache
after_destroy_commit :expire_chapters_sidebar_cache

def expire_chapters_sidebar_cache
  Rails.cache.delete('chapters-sidebar')
end

Using *_commit callbacks (rather than *_save/*_destroy) ensures the cache is only expired after the database transaction successfully commits, preventing stale reads.

Trade-offs

Pros:

• Fast page loads - sidebar is served from cache on every request
• Simple implementation - uses Rails' built-in fragment caching

Cons:

• All chapters share one cached fragment - adding/editing any chapter invalidates the entire sidebar
• Cache stampede potential if many requests hit while cache is cold/warming

Alternatives considered

• Cache per chapter: Would add complexity with more cache keys to manage
• Russian doll caching: Nested caching per-chapter, more complex to implement
• HTTP caching: Not appropriate here as content is dynamic per-user

For the current scale of ~10 chapters, a single cached fragment is the simplest effective solution.

Changes

• app/components/chapters_sidebar_component.rb - New ViewComponent
• app/components/chapters_sidebar_component.html.erb - ERB template with caching
• app/models/chapter.rb - Added cache expiration callbacks
• app/views/dashboard/show.html.haml - Use component instead of inline HAML
• spec/components/chapters_sidebar_component_spec.rb - Component tests
• spec/views/dashboard/show.html.haml_spec.rb - View integration tests
• spec/models/chapter_spec.rb - Cache expiration tests
• spec/rails_helper.rb - ViewComponent test configuration
• Gemfile - Added view_component gem

[olleolleolle]

Looks nice!

[olleolleolle]

didn't it work without this one?

[olleolleolle]

# Connect ViewComponent to RSpec, adding RSpec metadata type: :component.
#
# This extends Rails' own built-in (e.g. "type: :controller") metadata system.
RSpec::Rails::DIRECTORY_MAPPINGS[:component] = %w[ spec components ]

Something like this, in the rails_helper would auto-add the type: :component by file location.

in RSpec.config we'd need:

  # Automatically tag specs in conventional directories with matching type
  # metadata so that they have relevant helpers available to them.
  # See RSpec::Rails::DIRECTORY_MAPPINGS for details on which metadata is
  # applied to each directory.
  config.infer_spec_type_from_file_location!

[mroderick]

Thank you for the review @olleolleolle! I've addressed both of your suggestions:

1. Removed - You're right, ViewComponent::Base doesn't define initialize, so it's unnecessary. I added a rubocop:disable comment to silence the warning.

2. Added DIRECTORY_MAPPINGS - I've added to rails_helper.rb so that specs in spec/components/ automatically get the metadata inferred. This lets us remove the explicit from the spec file.

Appreciate the careful review!

[olleolleolle]

Thank you for introducing and using ViewComponent, it can be pretty handy.