variable "TAG" {default="" }

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

target "app" {
  context="."
  dockerfile="Dockerfile"
  tags = "${compact([
      "my-image:latest",
      notequal("",TAG) ? "my-image:${TAG}-1": "",
      notequal("",TAG) ? "my-image:${TAG}-2": null,
      null,
    ])}"
}

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

target "app" {
  context="."
  dockerfile="Dockerfile"
  tags = [
      "my-image:latest",
      notequal("",TAG) ? "my-image:${TAG}-1": "",
      notequal("",TAG) ? "my-image:${TAG}-2": "",
  ]
}

❯ docker buildx bake --print
{
   "target": {
      "app": {
         "context": ".",
         "dockerfile": "Dockerfile",
         "tags": [
            "my-image:latest"
         ]
      }
   }
}

❯ TAG="ok" docker buildx bake --print
{
   "target": {
      "app": {
         "context": ".",
         "dockerfile": "Dockerfile",
         "tags": [
            "my-image:latest",
            "my-image:ok-1",
            "my-image:ok-2"
         ]
      }
   }
}```