`docker buildx bake` does not support saving multiple targets to a single tarball

Contributing guidelines

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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

Attempting to output multiple targets to a single tarball results in a single random target being contained in the tarball, instead of all of them.

Expected behaviour

The generated tarball contains all images

Actual behaviour

The generated tarball contains a random image

Buildx version

github.com/docker/buildx 0.10.3 79e156beb11f697f06ac67fa1fb958e4762c0fab

Docker info

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  0.10.3
    Path:     /usr/lib/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  2.16.0
    Path:     /usr/lib/docker/cli-plugins/docker-compose

Server:
 Containers: 18
  Running: 1
  Paused: 0
  Stopped: 17
 Images: 691
 Server Version: 23.0.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: true
  Native Overlay Diff: false
  userxattr: false
 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 logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 2456e983eb9e37e47538f59ea18f2043c9a73640.m
 runc version: 
 init version: de40ad0
 Security Options:
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.2.1-arch1-1
 Operating System: Arch Linux
 OSType: linux
 Architecture: x86_64
 CPUs: 16
 Total Memory: 30.13GiB
 Name: pudge
 ID: 6IXA:H6AE:DQUM:AHGY:WMLU:ZWJQ:BOJX:LRKK:EOH4:UJ7Y:ZN23:WRMK
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Builders list

NAME/NODE           DRIVER/ENDPOINT             STATUS  BUILDKIT PLATFORMS
beautiful_shamir *  docker-container                             
  beautiful_shamir0 unix:///var/run/docker.sock running v0.10.5  linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
default             docker                                       
  default           default                     running 23.0.1   linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6

Configuration

With the following files,

docker-bake.hcl:

group "default" {
  targets = ["redis", "python"]
}

target "redis" {
    dockerfile = "Dockerfile_redis"
    output = ["type=docker,dest=images.tar"]
    tags = ["test_redis:latest"]
}

target "python" {
    dockerfile = "Dockerfile_python"
    output = ["type=docker,dest=images.tar"]
    tags = ["test_python:latest"]
}

Dockerfile_python:

FROM python:3.11-alpine

Dockerfile_redis:

FROM redis:7-alpine

docker buildx bake -f docker-bake.hcl

Logs

No response

Additional info

No response

Start with docker-bake.hcl, Dockerfile_redis, and Dockerfile_python, then run the reported docker buildx bake command to reproduce the tarball contents. Trace how the bake command handles multiple targets sharing type=docker,dest=images.tar, and consider the work complete when the generated tarball contains both images rather than one random target.