feat: add deprecation warning for v4 content collections in v5

[matthewp]

Changes

Emit console warning when collections are defined without a loader, signaling that they're using deprecated v4 backwards compatibility mode.

This helps users discover and migrate their legacy collections before upgrading to v6, where the escape hatch will require explicit opt-in with legacy.collectionsBackwardsCompat flag.

Testing

No changes

Docs

Not yet

[changeset-bot]

⚠️ No Changeset found

Latest commit: 22e658a

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[codspeed-hq]

CodSpeed Performance Report

Merging #14928 will not alter performance

_{Comparing feat/v5-collections-deprecation-warnings (22e658a) with main (4bceeb0)}

Summary

✅ 6 untouched

[HiDeoo]

Just to get the ball rolling, I guess the idea would be in a first step to throw an error when any of the possible reasons why automatic backwards compatibility might be enabled are detected. Not sure yet which error/format would be best suited for this but I assume that's something we can figure out on the way.

Regarding the possible reasons, from my understanding, automatic backwards compatibility might be enabled based on the list of reasons we have gathered in the v6 upgrade guide so far:

• a configuration file located at src/content/config.ts
• a collection that does not define a loader
• a collection that defines a collection type (type: 'content' or type: 'data')
• legacy collection querying methods getDataEntryById() and getEntryBySlug()
• legacy collection querying and rendering methods that depend on a slug property
• content rendered using entry.render()