setting DOCKER_HOST variable changes default builder

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

If I set DOCKER_HOST, it mysteriously overrides my default builder, even in other shells where DOCKER_HOST is not set.

Repro steps:

docker buildx create --name=buildx-multiarch --driver=docker-container
docker buildx use buildx-multiarch
DOCKER_HOST=unix:///home/nick/.docker/desktop/docker.sock docker buildx bake
docker buildx ls

Expected behaviour

After this sequence of commands, I would expect buildkit-multiarch to be the default builder.

Actual behaviour

My default builder has mysteriously changed to desktop-linux

Buildx version

github.com/docker/buildx v0.10.5 86bdced7766639d56baa4c7c449a4f6468490f87

Docker info

Client: Docker Engine - Community
 Version:    24.0.0
 Context:    desktop-linux
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.10.5
    Path:     /home/nick/.docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.18.1
    Path:     /usr/lib/docker/cli-plugins/docker-compose
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.0
    Path:     /usr/lib/docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.19
    Path:     /usr/lib/docker/cli-plugins/docker-extension
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v0.1.0-beta.4
    Path:     /usr/lib/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:     /usr/lib/docker/cli-plugins/docker-sbom
  scan: Docker Scan (Docker Inc.)
    Version:  v0.26.0
    Path:     /usr/lib/docker/cli-plugins/docker-scan
  scout: Command line tool for Docker Scout (Docker Inc.)
    Version:  v0.12.0
    Path:     /usr/lib/docker/cli-plugins/docker-scout
WARNING: Plugin "/home/nick/.docker/cli-plugins/docker-buildx-backup" is not valid: plugin candidate "buildx-backup" did not match "^[a-z][a-z0-9]*$"
WARNING: Plugin "/usr/lib/docker/cli-plugins/docker-compose.14.backup" is not valid: plugin candidate "compose.14.backup" did not match "^[a-z][a-z0-9]*$"

Server:
 Containers: 14
  Running: 8
  Paused: 0
  Stopped: 6
 Images: 196
 Server Version: 24.0.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 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 logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 3dce8eb055cbb6872793272b4f20ed16117344f8
 runc version: v1.1.7-0-g860f061
 init version: de40ad0
 Security Options:
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 5.15.49-linuxkit-pr
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 6
 Total Memory: 7.526GiB
 Name: docker-desktop
 ID: a92cef06-564f-4766-91bd-bc9e839af9fa
 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
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false

Builders list

docker buildx ls
NAME/NODE                  DRIVER/ENDPOINT  STATUS   BUILDKIT PLATFORMS
buildx-docker-container    docker-container                   
  buildx-docker-container0 desktop-linux    inactive          
buildx-multiarch           docker-container                   
  buildx-multiarch0        desktop-linux    running  v0.11.6  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  v0.11.6  linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/arm64, linux/riscv64, linux/ppc64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
desktop-linux *            docker                             
  desktop-linux            desktop-linux    running  v0.11.6  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

Doesn't matter. Even if there's no bake file and the build is an error, it still happens

Build logs

No response

Additional info

This is boiled down from a larger repro case where a script was invoking buildx with DOCKER_HOST and i couldn't figure out why the buildx builder was changing.

Start by tracing the docker buildx bake handling of DOCKER_HOST alongside the docker buildx use and docker buildx ls entry points, using the supplied command sequence to reproduce the builder change. Done means the selected builder remains buildx-multiarch when DOCKER_HOST is set only for the bake command, with coverage for the reported sequence.