always add but hide experimental cmds and flags

Signed-off-by: Victor Vieux <vieux@docker.com>

update cobra and use Tags

Signed-off-by: Victor Vieux <vieux@docker.com>

allow client to talk to an older server

Signed-off-by: Victor Vieux <vieux@docker.com>

command/system/cmd.go

@@ -1,8 +1,6 @@
 package system
 
 import (
-	"fmt"
-
 	"github.com/spf13/cobra"
 
 	"github.com/docker/docker/cli"
@@ -16,7 +14,8 @@ func NewSystemCommand(dockerCli *command.DockerCli) *cobra.Command {
 		Short: "Manage Docker",
 		Args:  cli.NoArgs,
 		Run: func(cmd *cobra.Command, args []string) {
-			fmt.Fprintf(dockerCli.Err(), "\n"+cmd.UsageString())
+			cmd.SetOutput(dockerCli.Err())
+			cmd.HelpFunc()(cmd, args)
 		},
 	}
 	cmd.AddCommand(
@@ -25,5 +24,6 @@ func NewSystemCommand(dockerCli *command.DockerCli) *cobra.Command {
 		NewDiskUsageCommand(dockerCli),
 		NewPruneCommand(dockerCli),
 	)
+
 	return cmd
 }

command/system/df.go

@@ -23,6 +23,7 @@ func NewDiskUsageCommand(dockerCli *command.DockerCli) *cobra.Command {
 		RunE: func(cmd *cobra.Command, args []string) error {
 			return runDiskUsage(dockerCli, opts)
 		},
+		Tags: map[string]string{"version": "1.25"},
 	}
 
 	flags := cmd.Flags()

command/system/prune.go

@@ -26,6 +26,7 @@ func NewPruneCommand(dockerCli *command.DockerCli) *cobra.Command {
 		RunE: func(cmd *cobra.Command, args []string) error {
 			return runPrune(dockerCli, opts)
 		},
+		Tags: map[string]string{"version": "1.25"},
 	}
 
 	flags := cmd.Flags()

command/system/version.go

@@ -1,6 +1,7 @@
 package system
 
 import (
+	"fmt"
 	"runtime"
 	"time"
 
@@ -70,10 +71,15 @@ func runVersion(dockerCli *command.DockerCli, opts *versionOptions) error {
 			Status: "Template parsing error: " + err.Error()}
 	}
 
+	APIVersion := dockerCli.Client().ClientVersion()
+	if defaultAPIVersion := dockerCli.DefaultVersion(); APIVersion != defaultAPIVersion {
+		APIVersion = fmt.Sprintf("%s (downgraded from %s)", APIVersion, defaultAPIVersion)
+	}
+
 	vd := types.VersionResponse{
 		Client: &types.Version{
 			Version:    dockerversion.Version,
-			APIVersion: dockerCli.Client().ClientVersion(),
+			APIVersion: APIVersion,
 			GoVersion:  runtime.Version(),
 			GitCommit:  dockerversion.GitCommit,
 			BuildTime:  dockerversion.BuildTime,