I've wished for a long time that Dockerfiles had an explicit way to define layers ripped off from (postgre)sql:

    BEGIN
    RUN foo
    RUN bar
    COMMIT

At the very real risk of talking out of my ass, the new versioned Dockerfile mechanism on top of builtkit should enable you to do that: https://github.com/moby/buildkit/blob/v0.15.0/frontend/docke...

In true "when all you have is a hammer" fashion, as very best I can tell that syntax= directive is pointing to a separate docker image whose job it is to read the file and translate it into builtkit api calls, e.g. https://github.com/moby/buildkit/blob/v0.15.0/frontend/docke...

But, again for clarity: I've never tried such a stunt, that's just the impression I get from having done mortal kombat with builtkit's other silly parts

    RUN <<EOF
    foo
    bar
    EOF

https://www.docker.com/blog/introduction-to-heredocs-in-dock...

Thanks, that helps a lot and I didn't know about it:) It's a touch less powerful than full transactions (because AFAICT you can't say merge a COPY and RUN together) but it's a big improvement.