Bake: confusing error message on multiple undefined variables

Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

The "docker-language-server" in Visual Studio Code is saying "Invalid expression (variable cycle not allowed to registry)"

I am not sure what this means.

All the examples in the docs use the same image for "cache-from" and "cache-to", so I am confused why I can't do that.

• https://docs.docker.com/build/bake/reference/#targetcache-from
• https://docs.docker.com/reference/cli/docker/buildx/build/#cache-from
• https://github.com/moby/buildkit#registry-push-image-and-cache-separately
• https://docs.docker.com/build/cache/backends/#multiple-caches

target "ubuntu" {
  context = "ci/ubuntu"
  name = sanitize("ubuntu_${ubuntu_version.to}")
  tags = ["${HARBOR_REGISTRY_PREFIX}/ci/ubuntu:${ubuntu_version.to}"]
  matrix = {
    ubuntu_version = [
      {
        from = "noble"
        to = "noble-rootless"
      },
      {
        from = "jammy"
        to = "jammy-rootless"
      },
      {
        from = "focal"
        to = "focal-rootless"
      }
    ]
  }
  args = {
    FROM_TAG = ubuntu_version.from
  }
  inherits = ["_common"]
  cache-to = [
    {
      type=registry,
      ref="${HARBOR_REGISTRY_PREFIX}/ci/ubuntu:${ubuntu_version.to}-build-cache",
      mode=max,
    },
  ]
  cache-from = [ 
    {
      type=registry,
      ref="${HARBOR_REGISTRY_PREFIX}/ci/ubuntu:${ubuntu_version.to}-build-cache"
    },
  ]
}

Expected behaviour

I expect the build cache to be pushed to "${HARBOR_REGISTRY_PREFIX}/ci/ubuntu:${ubuntu_version.to}-build-cache" and pulled from the same place.

Actual behaviour

The "docker-language-server" in Visual Studio Code is saying "Invalid expression (variable cycle not allowed to registry)"

Buildx version

github.com/docker/buildx v0.23.0 28c90ea

Docker info

Client: Docker Engine - Community
 Version:    28.1.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.23.0
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.35.1
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 4
  Running: 1
  Paused: 0
  Stopped: 3
 Images: 34
 Server Version: 28.1.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: true
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 05044ec0a9a75232cad458027ca83437aae3f4da
 runc version: v1.2.5-0-g59923ef
 init version: de40ad0
 Security Options:
  seccomp
   Profile: builtin
  rootless
  cgroupns
 Kernel Version: 6.11.0-24-generic
 Operating System: Ubuntu 24.04.2 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 12
 Total Memory: 31.05GiB
 Name: mhm
 ID: 24f3ada6-172a-47d5-bbf0-25f34f871c96
 Docker Root Dir: /home/mhm/.local/share/docker
 Debug Mode: false
 Experimental: false
 Insecure Registries:
  ::1/128
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No cpuset support
WARNING: No io.weight support
WARNING: No io.weight (per device) support
WARNING: No io.max (rbps) support
WARNING: No io.max (wbps) support
WARNING: No io.max (riops) support
WARNING: No io.max (wiops) support

Builders list

NAME/NODE               DRIVER/ENDPOINT                         STATUS    BUILDKIT   PLATFORMS
docker-container        docker-container                                             
 \_ docker-container0    \_ unix:///run/user/1000/docker.sock   running   v0.20.2    linux/amd64 (+3), linux/386
remote                  remote                                                       
 \_ remote0              \_ tcp://redacted-company-buildkit-server:1234         running   v0.21.0    linux/amd64 (+3), linux/386
default*                docker                                                       
 \_ default              \_ default                             running   v0.21.0    linux/amd64 (+3), linux/386
rootless                docker                                                       
 \_ rootless             \_ rootless                            running   v0.21.0    linux/amd64 (+3), linux/386

Configuration

mhm@mhm:~/Documents/continuous-integration$ time docker buildx bake --set=*.target=test --set=*.output=type=cacheonly ubuntu
[+] Building 0.0s (0/1)                                                                                                                                              docker:default
 => [internal] load local bake definitions                                                                                                                                     0.0s
docker-bake.hcl:67
[+] Building 0.0s (1/1) FINISHED                                                                                                                                     docker:default
 => [internal] load local bake definitions                                                                                                                                     0.0s
 => => reading docker-bake.hcl 15.93kB / 15.93kB                                                                                                                               0.0s
  67 | >>>   cache-to = [
  68 | >>>     {
  69 | >>>       type=registry,
  70 | >>>       ref="${HARBOR_REGISTRY_PREFIX}/ci/ubuntu:${ubuntu_version.to}-build-cache",
  71 | >>>       mode=max,
  72 | >>>     },
  73 | >>>   ]
  74 |       cache-from = [ 
--------------------
ERROR: docker-bake.hcl:67,14-73,4: Invalid expression; variable cycle not allowed for registry

real    0m0.125s
user    0m0.120s
sys     0m0.039s

Build logs

Additional info

No response