fix: remove legacy content collections

[ascorbic]

Changes

Closes #14361.

This PR removes a number of APIs and options related to legacy content collections that were deprecated in Astro 5, including:

• The legacy.collections option, which was added in Astro 5 and caused the old content collections system to be used instead of the new one.
• Deprecated functions from astro:content: getEntryBySlug and getDataEntryById are both replaced by getEntry(), which is a drop-in replacement for both.
• Support for the old src/content/config.* file location. You must now use src/content.config.*.
• Automatically generating collections when a src/content/ directory is present and no content config file exists. You must now explicitly define collections in src/content.config.*.
• Support for collections without a loader. You must now use the glob() loader to create collections from filesystem content. This will also mean that generated entries use the new entry format:
  • The id field is now a slug, not a filename. You can access the filename via entry.filePath, which is the path relative to the site root.
  • There is no longer a slug field – use id instead.
  • You can no longer call entry.render() on content entries. Use render(entry) instead, imported from astro:content.

Testing

Literally hundreds of updated tests! We never updated lots of the fixtures in Astro 5, instead relying on the legacy support. This PR takes the plunge and does the update.

A lot of tests are failing in next, so it's not always 100% clear if there are more that need updating. I think I've found them all though.

Docs

The docs already reflect the current behaviour. The upgrade guide is in progress.

[changeset-bot]

🦋 Changeset detected

Latest commit: beeeff1

The changes in this PR will be included in the next version bump.

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[github-actions]

This PR is blocked because it contains a major changeset. A reviewer will merge this at the next release if approved.

[florian-lefebvre]

For each API that has a deprecation helper instead of just not existing anymore (eg getEntryById), can you add a todo comment so we don't forget to remove them later on? Maybe a comment for v7

[florian-lefebvre]

FYI there's still this todo here