Mark checkpoint feature as Linux-only, and homogenize error messages

This patch adds annotations to mark the checkpoint commands as Linux only, which
hides them if the daemon is running a non-matching operating-system type;

Before:

    docker

    Usage:	docker COMMAND

    A self-sufficient runtime for containers

    ...

    Management Commands:
      config      Manage Docker configs
      container   Manage containers
      image       Manage images

After:

    docker

    Usage:	docker COMMAND

    A self-sufficient runtime for containers

    ...

    Management Commands:
      checkpoint  Manage checkpoints
      config      Manage Docker configs
      container   Manage containers
      image       Manage images

This change also prints errors when attempting to use checkpoint commands or
flags if the feature is not supported by the Daemon's operating system;

    $ docker checkpoint --help
    docker checkpoint is only supported on a Docker daemon running on linux, but the Docker daemon is running on windows

    $ docker checkpoint create --help
    docker checkpoint create is only supported on a Docker daemon running on linux, but the Docker daemon is running on windows

    $ docker checkpoint ls --help
    docker checkpoint ls is only supported on a Docker daemon running on linux, but the Docker daemon is running on windows

    $ docker checkpoint rm --help
    docker checkpoint rm is only supported on a Docker daemon running on linux, but the Docker daemon is running on windows

    $ docker container start --checkpoint=foo mycontainer
    "--checkpoint" requires the Docker daemon to run on linux, but the Docker daemon is running on windows

    $ docker container start --checkpoint-dir=/foo/bar mycontainer
    "--checkpoint-dir" requires the Docker daemon to run on linux, but the Docker daemon is running on windows

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/checkpoint/cmd.go

@@ -9,11 +9,15 @@ import (
 // NewCheckpointCommand returns the `checkpoint` subcommand (only in experimental)
 func NewCheckpointCommand(dockerCli command.Cli) *cobra.Command {
 	cmd := &cobra.Command{
-		Use:         "checkpoint",
+		Use:   "checkpoint",
-		Short:       "Manage checkpoints",
+		Short: "Manage checkpoints",
-		Args:        cli.NoArgs,
+		Args:  cli.NoArgs,
-		RunE:        command.ShowHelp(dockerCli.Err()),
+		RunE:  command.ShowHelp(dockerCli.Err()),
-		Annotations: map[string]string{"experimental": "", "version": "1.25"},
+		Annotations: map[string]string{
+			"experimental": "",
+			"ostype":       "linux",
+			"version":      "1.25",
+		},
 	}
 	cmd.AddCommand(
 		newCreateCommand(dockerCli),

cli/command/container/start.go

@@ -47,8 +47,10 @@ func NewStartCommand(dockerCli command.Cli) *cobra.Command {
 
 	flags.StringVar(&opts.checkpoint, "checkpoint", "", "Restore from this checkpoint")
 	flags.SetAnnotation("checkpoint", "experimental", nil)
+	flags.SetAnnotation("checkpoint", "ostype", []string{"linux"})
 	flags.StringVar(&opts.checkpointDir, "checkpoint-dir", "", "Use a custom checkpoint storage directory")
 	flags.SetAnnotation("checkpoint-dir", "experimental", nil)
+	flags.SetAnnotation("checkpoint-dir", "ostype", []string{"linux"})
 	return cmd
 }
 

cmd/docker/docker.go

@@ -256,6 +256,9 @@ func hideUnsupportedFeatures(cmd *cobra.Command, details versionDetails) {
 		if subcmdVersion, ok := subcmd.Annotations["version"]; ok && versions.LessThan(clientVersion, subcmdVersion) {
 			subcmd.Hidden = true
 		}
+		if v, ok := subcmd.Annotations["ostype"]; ok && v != osType {
+			subcmd.Hidden = true
+		}
 	}
 }
 
@@ -282,14 +285,14 @@ func areFlagsSupported(cmd *cobra.Command, details versionDetails) error {
 				return
 			}
 			if !isOSTypeSupported(f, osType) {
-				errs = append(errs, fmt.Sprintf("\"--%s\" requires the Docker daemon to run on %s, but the Docker daemon is running on %s", f.Name, getFlagAnnotation(f, "ostype"), osType))
+				errs = append(errs, fmt.Sprintf("\"--%s\" is only supported on a Docker daemon running on %s, but the Docker daemon is running on %s", f.Name, getFlagAnnotation(f, "ostype"), osType))
 				return
 			}
 			if _, ok := f.Annotations["experimental"]; ok && !hasExperimental {
 				errs = append(errs, fmt.Sprintf("\"--%s\" is only supported on a Docker daemon with experimental features enabled", f.Name))
 			}
 			if _, ok := f.Annotations["experimentalCLI"]; ok && !hasExperimentalCLI {
-				errs = append(errs, fmt.Sprintf("\"--%s\" is only supported when experimental cli features are enabled", f.Name))
+				errs = append(errs, fmt.Sprintf("\"--%s\" is on a Docker cli with experimental cli features enabled", f.Name))
 			}
 			_, isKubernetesAnnotated := f.Annotations["kubernetes"]
 			_, isSwarmAnnotated := f.Annotations["swarm"]
@@ -310,6 +313,7 @@ func areFlagsSupported(cmd *cobra.Command, details versionDetails) error {
 // Check recursively so that, e.g., `docker stack ls` returns the same output as `docker stack`
 func areSubcommandsSupported(cmd *cobra.Command, details versionDetails) error {
 	clientVersion := details.Client().ClientVersion()
+	osType := details.ServerInfo().OSType
 	hasExperimental := details.ServerInfo().HasExperimental
 	hasExperimentalCLI := details.ClientInfo().HasExperimental
 	hasKubernetes := details.ClientInfo().HasKubernetes()
@@ -319,11 +323,14 @@ func areSubcommandsSupported(cmd *cobra.Command, details versionDetails) error {
 		if cmdVersion, ok := curr.Annotations["version"]; ok && versions.LessThan(clientVersion, cmdVersion) {
 			return fmt.Errorf("%s requires API version %s, but the Docker daemon API version is %s", cmd.CommandPath(), cmdVersion, clientVersion)
 		}
+		if os, ok := curr.Annotations["ostype"]; ok && os != osType {
+			return fmt.Errorf("%s is only supported on a Docker daemon running on %s, but the Docker daemon is running on %s", cmd.CommandPath(), os, osType)
+		}
 		if _, ok := curr.Annotations["experimental"]; ok && !hasExperimental {
 			return fmt.Errorf("%s is only supported on a Docker daemon with experimental features enabled", cmd.CommandPath())
 		}
 		if _, ok := curr.Annotations["experimentalCLI"]; ok && !hasExperimentalCLI {
-			return fmt.Errorf("%s is only supported when experimental cli features are enabled", cmd.CommandPath())
+			return fmt.Errorf("%s is only supported on a Docker cli with experimental cli features enabled", cmd.CommandPath())
 		}
 		_, isKubernetesAnnotated := curr.Annotations["kubernetes"]
 		_, isSwarmAnnotated := curr.Annotations["swarm"]