enhancement: show when context is overridden by "DOCKER_HOST" or other options

Bắt đầu bằng cách đọc cli/command/cli.go và logic cảnh báo trong cli/command/context/list.go và cli/command/context/use.go. So sánh cách docker version và docker info hiện báo cáo Context, sau đó xác định hành vi đầu ra và định dạng cho các Context bị ghi đè và các Host đang hoạt động. Được xem là hoàn tất khi thiết kế giải quyết các phương án còn bỏ ngỏ mà không làm hỏng đầu ra đã định dạng hoặc các kỳ vọng của script.

Description

The Docker CLI defaults to using a local daemon through a unix-socket (Linux, macOS) or named pipe (Windows), but it can be configured to use a different connection, which can be a remote machine.

There's various ways to configure the CLI; (also see DockerCli.CurrentContext);

• DOCKER_HOST (takes precedence over context)
• --host / -H (configures the connection to use)
• DOCKER_CONTEXT (configure the context, which is used to configure the connection)
• --context (configure the context, which is used to configure the connection)
• currentContext field in ~/.docker/config.json (configures the default context to configure the connection)
• In rootless-mode, other env-vars may be involved for the default socket path.

Some of these options may not be very visible; we have some warnings when performing docker context operations to inform the user that DOCKER_HOST is set (and overrides the selected context);
https://github.com/docker/cli/blob/1d768f8983f90abaf7065c76102312eb2ffc42a4/cli/command/context/list.go#L110-L113
https://github.com/docker/cli/blob/1d768f8983f90abaf7065c76102312eb2ffc42a4/cli/command/context/use.go#L52-L55

However, other places may not show this information. Most notably docker version and docker info;

Current context (in the CLI's config) is desktop-linux;

cat ~/.docker/config.json | jq .currentContext
"desktop-linux"

However, docker version shows that the default context is used;

docker version
Client:
 Version:           28.3.0-rc.1
 API version:       1.42 (downgraded from 1.51)
 Go version:        go1.24.4
 Git commit:        f53bb88
 Built:             Fri Jun 13 18:25:06 2025
 OS/Arch:           darwin/arm64
 Context:           default

And docker info does the same;

docker info | head -n 5
Client:
 Version:    28.3.0-rc.1
 Context:    default
 Debug Mode: false
 Plugins:

In the above situation, the reason was that DOCKER_HOST was set in the current shell;

env | grep DOCKER
DOCKER_HOST=ssh://swarm-test-01/var/run/docker.sock

Improvement: make active connection more visible

⚠️ This is just a draft; detailed design still needed

1. Include "Docker Host" in docker version and docker info

We can include the active host in output of docker version and docker info;

docker version
Client:
 Version:           28.3.0-rc.1
 API version:       1.42 (downgraded from 1.51)
 Go version:        go1.24.4
 Git commit:        f53bb88
 Built:             Fri Jun 13 18:25:06 2025
 OS/Arch:           darwin/arm64
 Context:           default
 Docker Host:       ssh://swarm-test-01/var/run/docker.sock

docker info | head -n 5
Client:
 Version:     28.3.0-rc.1
 Context:     default
 Docker Host: ssh://swarm-test-01/var/run/docker.sock
 Debug Mode:  false

• ☝️ alternatively, we could include this in the Server section, however, the Server itself may be serving the API on multiple "hosts" (e.g. both on a socket AND through tcp); https://github.com/moby/moby/pull/43459

2. Show what determined the active context

We can show "why" the given context is used, e.g.;

 Context:           default (context disabled because DOCKER_HOST is set)

 Context:           desktop-linux (from DOCKER_CONTEXT)

 Context:           desktop-linux (from "~/.docker/config.json`)

⚠️ the above output may be used by users in scripting (docker version | grep 'Context:');

• Generally, users should use docker context show for this, but it may be a breaking change
• When formatting, we should make this a separate part of the template so that docker version --format '{{.Client.Context}}' only shows the context name (same for `docker info --format``)

3. Show what determined the active "host" connection

Similar to the above; show where the connection string came from;

 Docker Host:       ssh://swarm-test-01/var/run/docker.sock (from DOCKER_HOST)

❓ should we also show if this comes from the active context? (when not overridden by DOCKER_HOST)? Or is that just "noise"?

 Docker Host:       ssh://swarm-test-01/var/run/docker.sock (from "desktop-linux" context)

or

 Docker Host:       ssh://swarm-test-01/var/run/docker.sock (from current context)