feature: Nested pages

[jbmoelker]

Changes

• Adds migration to add a 'Parent page' field to the Page model.
• Adds reusable ParentPage fragment to handle deeply nested pages consistently in GraphQL queries.
• Adds helpers to list parent pages, get nested page slugs and get page path for consistent URLs (in InternalLinks, Breadcrumbs, canonical and alternate links, etc).
• Adds a Breadcrumb component to the Default layout for context and navigation.

Associated issue

Resolves #13 .

How to test

1. Open preview link
2. Navigate to a nested page like /en/overview-page/page-1/, /en/overview-page/demos/tables/, /nl/-/-/tabellen/.
3. Verify pages load, their URLs are constructed using their slugs and those of their parent pages.
4. Verify parent pages unavailable in a specific locale are replaced with a dash in the URL (like /nl/-/-/tabellen/).
5. Verify locale switcher works on nested pages
6. Verify breadcrumb navigation works (for example on /en/overview-page/demos/tables/ or /en/search/?query=heading).
7. Verify URLs and navigation still work on pages that are not nested.

Checklist

• [x] I have performed a self-review of my own code
• [x] I have made sure that my PR is easy to review (not too big, includes comments) 🤷 , complex feature, as easy as I got make it.
• [x] I have made updated relevant documentation files (in project README, docs/, etc)
• [x] I have added a decision log entry if the change affects the architecture or changes a significant technology
• [x] I have notified a reviewer

[cloudflare-pages[bot]]

Deploying with    Cloudflare Pages

Latest commit:	ed1e696
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Preview URL:	https://06b7b467.head-start.pages.dev
Branch Preview URL:	https://feat-nested-pages.head-start.pages.dev

View logs

[jbmoelker]

@decrek and @phortuin mentioned the use use of a placeholder for missing parent pages, when a parent page is unavailable in a given locale, currently filled with - (like /-/page-slug/) is odd. @decrek prefers builds to fail if translation of a parent page is missing for a given locale.

I agree having non-translated parent pages is undesirable. However this is a consequence of making all locales optional. For now, I would leave this up to content editors. If we have a better solution in the future, we can create a PR for that. For now, I'm merging this one so we have a working solution.

[phortuin]

\o/

prefers builds to fail if translation of a parent page is missing for a given locale this is a consequence of making all locales optional

Yeah, agree that build should not fail on optional content. Also, it's a realistic scenario that a website has pages in a certain locale only (product is only sold in certain countries; blog posts that are not translated... know any company that does that?) and the nesting of pages should have no relation to existing locales.

Use case below is improbable but not unthinkable:

• /en-uk/jams/strawberry/ ← strawberry jam is only sold in the uk
• /en-uk/jams/strawberry/contest/ ← yay, a contest
• /hi-in/-/-/contest/ ← contest is also in Hindi for UK residents that don't speak English, but jams aren't sold in India