How to do optional Tags in bake?

[AnthonyPoschen]

I am trying to only add tags if a variable is none empty, primarily fetching if the git commit has a version tag and if so i would like to push that tag. below is an example bake file demonstrating where i am at.

variable "TAG" {default="" }

group "default" {
	targets = [
    "app",
  ]
}

target "app" {
  context="."
  dockerfile="Dockerfile"
  tags = [
    "my-image:latest",
    notequal("",TAG) ? "my-image:${TAG}": null,
  ]
}

null type is not allowed in arrays. An empty string will throw an error in the docker build. Not sure how to implement optional entries into an array. I also could not find a way to do appending with the tags assign.

wonder if it would be wiser to have empty strings be ignored for tagging to allow empty string results.

[AnthonyPoschen]

the following function should be able to resolve this

https://github.com/zclconf/go-cty/blob/main/cty/function/stdlib/collection.go#L265

resulting tags block would probably look like

tags = "${compact(["myimage",null,""])}"

is it easy to multi line?

[AnthonyPoschen]

Raised a PR which offers 2 solutions in one to allow conditional tag inclusions. p.s i have really enjoyed using buildx to reduce build complexity :)