Specifing `docker --config` option breaks `docker buildx build` command

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

I use different DOCKER_CONFIG directories to switch among different tenants of the same Container Registry.

Recently, I found that when I set the DOCKER_CONFIG directory parameter, whether through the --config parameter or the DOCKER_CONFIG environment variable, the docker buildx build command parameter parsing will be completely messed up, reporting that --platform, -t and other parameters cannot be recognized.

Expected behaviour

Command like

docker --config /path/to/custom-config-dir buildx build --platform linux/amd64 -t myimage1 -t myimage2 --build-arg APP_NAME=server --push .

should work

Actual behaviour

An error raised:

unknown flag: --platform
See 'docker --help'.

Usage:  docker [OPTIONS] COMMAND

A self-sufficient runtime for containers

Common Commands:
  run         Create and run a new container from an image
  exec        Execute a command in a running container
...

When I omit --config option, everything works.

Even if I set DOCKER_CONFIG environment variable, it will also fall.

Buildx version

github.com/docker/buildx v0.16.2-desktop.1 081c21b9e461293ae243a1ff813a680a4f5f8fb9

Docker info

Client:
 Version:    27.2.0
 Context:    desktop-linux
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.16.2-desktop.1
    Path:     /Users/myusername/.docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.29.2-desktop.2
    Path:     /Users/myusername/.docker/cli-plugins/docker-compose
  debug: Get a shell into any image or container (Docker Inc.)
    Version:  0.0.34
    Path:     /Users/myusername/.docker/cli-plugins/docker-debug
  desktop: Docker Desktop commands (Alpha) (Docker Inc.)
    Version:  v0.0.15
    Path:     /Users/myusername/.docker/cli-plugins/docker-desktop
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.2
    Path:     /Users/myusername/.docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.25
    Path:     /Users/myusername/.docker/cli-plugins/docker-extension
  feedback: Provide feedback, right in your terminal! (Docker Inc.)
    Version:  v1.0.5
    Path:     /Users/myusername/.docker/cli-plugins/docker-feedback
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v1.3.0
    Path:     /Users/myusername/.docker/cli-plugins/docker-init
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     /Users/myusername/.docker/cli-plugins/docker-sbom
  scout: Docker Scout (Docker Inc.)
    Version:  v1.13.0
    Path:     /Users/myusername/.docker/cli-plugins/docker-scout

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 0
 Server Version: 27.2.0
 Storage Driver: overlayfs
  driver-type: io.containerd.snapshotter.v1
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 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: 8fc6bcff51318944179630522a095cc9dbf9f353
 runc version: v1.1.13-0-g58aa920
 init version: de40ad0
 Security Options:
  seccomp
   Profile: unconfined
  cgroupns
 Kernel Version: 6.10.4-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: aarch64
 CPUs: 8
 Total Memory: 7.655GiB
 Name: docker-desktop
 ID: 9b936eee-5f78-458b-adf1-6c115f5a42e0
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Labels:
  com.docker.desktop.address=unix:///Users/myusername/Library/Containers/com.docker.docker/Data/docker-cli.sock
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: daemon is not using the default seccomp profile

Builders list

-> % docker buildx ls
NAME/NODE           DRIVER/ENDPOINT     STATUS    BUILDKIT   PLATFORMS
default             docker                                   
 \_ default          \_ default         running   v0.15.2    linux/arm64, linux/amd64, linux/amd64/v2, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64
desktop-linux*      docker                                   
 \_ desktop-linux    \_ desktop-linux   running   v0.15.2    linux/arm64, linux/amd64, linux/amd64/v2, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64

Configuration

FROM alpine:3.20

ARG APP_NAME="server"

ENV TZ="Asia/Shanghai"

RUN apk add --no-cache tini ca-certificates tzdata curl && \
    ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && \
    echo $TZ > /etc/timezone

ENTRYPOINT [ "/sbin/tini", "--" ]

WORKDIR /data

ADD ${APP_NAME} /${APP_NAME}
RUN chmod +x /${APP_NAME}

ENV APP_NAME="${APP_NAME}"

CMD [ "sh", "-c", "exec /${APP_NAME}" ]

Build logs

No response

Additional info

No response

Start by reproducing the command with docker --config and with DOCKER_CONFIG, then compare argument handling for docker buildx build when the configuration option is absent. Trace the Docker CLI option parsing entry point and the buildx command invocation; done means --platform, -t, --build-arg, --push, and the build context are parsed and passed correctly in both cases.