I have a job that builds a matrix of PHP versions, base distros (and some other stuff IRL). I want to combine it into one bake, but still source the versions from env vars. I'm not sure if there's a way to do this in bake, or if I need to generate HCL/JSON separately?

I could generate the default group pretty easily if I set an env var like PHP_VERSIONS=7,8 DISTROS =alpine,ubuntu:

variable PHP_VERSIONS {}
variable DISTROS {}

group "default" {
  targets = flatten(
    [for d in split(",", "${DISTROS}"):
      [for v in split(",", "${PHP_VERSIONS}"):
        "${d}-php-${v}"
      ]
    ]
  )
}

However I can't see how to avoid explicitly enumerating all the targets:

target "alpine-php-8" {}
[...etc...]

Ideally I'd have some way to template the targets, is there anything possible in bake's HCL?