install/uninstall: allow aliasing buildx to docker builder

Currently the user can type `docker buildx` to use this tool.
This patch allows the user to install buildx as a `docker builder` alias.

As an additional benefit, this allows the regular `docker build` to hook
into `buildx build`.

Note that the install and uninstall commands are currently hidden.

Signed-off-by: Tibor Vass <tibor@docker.com>

commands/uninstall.go

@@ -0,0 +1,58 @@
+package commands
+
+import (
+	"os"
+
+	"github.com/docker/cli/cli"
+	"github.com/docker/cli/cli/command"
+	"github.com/docker/cli/cli/config"
+	"github.com/pkg/errors"
+	"github.com/spf13/cobra"
+)
+
+type uninstallOptions struct {
+}
+
+func runUninstall(dockerCli command.Cli, in uninstallOptions) error {
+	dir := config.Dir()
+	cfg, err := config.Load(dir)
+	if err != nil {
+		return errors.Wrap(err, "could not load docker config to uninstall 'docker builder' alias")
+	}
+	// config.Load does not return an error if config file does not exist
+	// so let's detect that case, to avoid writing an empty config to disk.
+	if _, err := os.Stat(cfg.Filename); err != nil {
+		if !os.IsNotExist(err) {
+			// should never happen, already handled in config.Load
+			return errors.Wrap(err, "unexpected error loading docker config")
+		}
+		// no-op
+		return nil
+	}
+
+	delete(cfg.Aliases, "builder")
+	if len(cfg.Aliases) == 0 {
+		cfg.Aliases = nil
+	}
+
+	if err := cfg.Save(); err != nil {
+		return errors.Wrap(err, "could not write docker config")
+	}
+	return nil
+}
+
+func uninstallCmd(dockerCli command.Cli) *cobra.Command {
+	var options uninstallOptions
+
+	cmd := &cobra.Command{
+		Use:   "uninstall",
+		Short: "Uninstall the 'docker builder' alias",
+		Args:  cli.ExactArgs(0),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return runUninstall(dockerCli, options)
+		},
+		Hidden: true,
+	}
+
+	return cmd
+}