I2D: Deprecate "-latest" Binaries

Summary

Context: Following up on an old comment https://github.com/ampproject/amphtml/issues/21135#issuecomment-467998527

The original intention was that if we create a new version of a component which maintains backward compatibility, we could then simply modify the “-latest” pointer to the new version. Publisher documents could then seamlessly get the new version with no action on their part.

In practice we don’t create a new version of a components unless we are explicitly making breaking changes. This means that bumping the pointer is impossible as it will more than likely break current consumers (as happened in the past). Therefore the -latest binaries have serve no practical purpose and we should remove them.

Deprecation Plan

1. Modify the documentation for -latest binaries on amp.dev to point out that it is deprecated.
2. Any new components created should not allow -latest via validator rules.
3. Add a validator warnings for pages using -latest binaries, recommending publishers pin to a specific extension version.
4. Simplify the configuration in our bundles configuration s.t. they only provide a latestVersion when it isn’t the value 0.1
5. ~Eventually, if usage is low enough, remove the binaries entirely. (cc @honeybadgerdontcare). Less than 1 in 1,000 would be “low enough”.~ removed based on discussion from design review.

Notifications

/cc @ampproject/wg-approvers

[schlessera]

Another use case that has its own set of challenges is that we want to work on automatically replacing slow components (like a popular React slider known to be bad for performance) with more performant (Bento) AMP components as part of the Page Experience Engine. In this case, we’d always want to stick with the latest stable version, but have the generated logic be adapted as needed with version changes.

[Gregable]

For approval, I’d like to see some explicitly recommended metric for “usage is low enough”. Given that we’d be breaking existing pages with usage, I would only approve it was extremely low. For example, fewer than 1 in 1,000 documents which include that particular component.