Use a consistent parenting strategy for page translations

[taylor-steve]

Fixes #3533

I believe these these two tests represent incompatible notions of page parent relationships:

spotlight/spec/models/spotlight/page_spec.rb

Lines 243 to 247 in e48b227

	it 'updates the translated child pages with the correct parent association' do
	expect(child_page_es.parent_page).to eq parent_page
	parent_page_es.save
	expect(child_page_es.reload.parent_page).to eq parent_page_es
	end

spotlight/spec/models/spotlight/page_spec.rb

Lines 297 to 300 in e48b227

	it 'removes the parent page id when the child page is set to an as-yet-untranslated parent page' do
	child_page.update(parent_page: another_page)
	expect(child_page_es.reload.parent_page).to be_nil
	end

The first test suggests that a translated child page can and should point its parent_page at the default locale parent page when there is no translated parent page available.

The second test suggests that translated children should have a nil parent relationship when the translated parent is missing.

I think this all might be somewhat awkwardly modeled, but nil parent relationships make more sense for our existing code.

This bug was caused by a discrepancy with the parent handling between:

spotlight/app/models/spotlight/page.rb

Lines 154 to 167 in e48b227

	def clone_for_locale(locale)
	dup.tap do |np|
	np.locale = locale
	np.default_locale_page = self
	np.published = false
	np.slug = slug
	if !top_level_page? && (parent_translation = parent_page.translated_page_for(locale)).present?
	np.parent_page = parent_translation
	end
	child_pages.for_locale(locale).update(parent_page: np) if top_level_page? && respond_to?(:child_pages)
	end
	end

and:

spotlight/app/models/spotlight/page.rb

Lines 171 to 182 in e48b227

	def update_translated_pages_weights_and_parent_page
	return unless locale.to_sym == I18n.default_locale
	if saved_change_to_parent_page_id?
	translated_pages.find_each do |translated_page|
	parent_translation = parent_page&.translated_page_for(translated_page.locale)
	translated_page.update(parent_page_id: parent_translation&.id)
	end
	end
	translated_pages.update(weight:) if saved_change_to_weight?
	end

This PR would effectively mean you'd use locale to shift laterally between fully independent trees of feature pages

Checking if you have translated pages that would be impacted

In a Rails console in your Spotlight app:

translated_pages = Spotlight::Page.where.not(locale: I18n.default_locale).where.not(parent_page_id: nil)

pages_with_the_bug = translated_pages.select { |page| page.parent_page&.locale&.to_sym == I18n.default_locale }

If you have impacted pages (pages_with_the_bug.length > 0) you have two choices:

• add translations for all the parent pages of the pages_with_the_bug pages
• set the parent_page relationship to nil for all pages_with_the_bug pages

Potential Future Work

This PR only serves to establish consistency in how we treat page parent relationships, it does not address the somewhat odd behavior than can arise from how they are currently modeled. Take this example, where all pages with the exception of FP 3 have French translations:

When viewing the exhibit in French the ordering can differ significantly from the default locale because of the mismatch between the page trees and the weights being considered.

The Spotlight community may want to revisit if this current page translation approach is meeting their needs or if moving to a more simple approach would suffice.