I'll get this merged, but what is potentially breaking about switching to the heroku/builder image?

@josegonzalez Thank you for the merge. The breaking differences between the various images are:

• The heroku/buildpacks:* images contain a mixture of native CNBs and shimmed classic buildpacks. In contrast for the new images, we've split out the shimmed and native buildpacks into two separate builder namespaces: heroku/builder:* and heroku/builder-classic:*. For now (until we finish more CNBs), heroku/buildpacks:* supports a couple more languages/tools (PHP, Gradle) than the heroku/builder:* images.
• The heroku/builder:* and heroku/builder-classic:* images only support Heroku-22+, meaning that switching to them requires upgrading from Heroku-20 to Heroku-22 too.
• The native CNBs for some languages have used this opportunity to drop old features (eg old versions of Rails in the case of the Ruby buildpack iirc), or haven't quite added support for all features yet (eg automatic Django collectstatic support is not yet finished for the Python CNB)

The feature parity and language support differences will reduce over the coming months as we finish/polish the native CNBs.

See also the image descriptions under the table here:
https://github.com/heroku/builder#heroku-builder-images

That is, it would be great if Dokku eventually switched the default to heroku/builder:22, however, if that was done right now, then for a small subset of people that would be a breaking change, and they would need to instead switch to heroku/builder-classic:22 until the feature parity/language support of heroku/builder:22 is improved.

Switching the Dokku default now might be something you want to do anyway (depending on how many people rely on the defaults, your appetite for risk, and how many Dokku users you think might read the release notes clearly etc), but I wanted to at least keep this initial change simple, since it unblocks me deleting the (no longer updated, and IMO footgun-prone) latest tag :-)

I'll get a patch release out in a day or two, after which you can probably remove the image. If it breaks for folks, we have a workaround folks can use to switch to a supported builder.

I think moving to the heroku/builder:22 might make sense in the next minor release.

Also, thank you for the explanation, that makes a ton of sense!