build: only show buildkit-specific flags if buildkit is enabled

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

Author: Tibor Vass

cli/command/cli.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"time"
 
 	"github.com/docker/cli/cli"
@@ -56,6 +57,7 @@ type Cli interface {
 	RegistryClient(bool) registryclient.RegistryClient
 	ContentTrustEnabled() bool
 	NewContainerizedEngineClient(sockPath string) (clitypes.ContainerizedClient, error)
+	BuildKitEnabled() (bool, error)
 }
 
 // DockerCli is an instance the docker command line client.
@@ -69,6 +71,7 @@ type DockerCli struct {
 	serverInfo            ServerInfo
 	clientInfo            ClientInfo
 	contentTrust          bool
+	buildkitEnabled       *bool
 	newContainerizeClient func(string) (clitypes.ContainerizedClient, error)
 }
 
@@ -133,6 +136,23 @@ func (cli *DockerCli) ContentTrustEnabled() bool {
 	return cli.contentTrust
 }
 
+// BuildKitEnabled returns whether buildkit is enabled either through a daemon setting
+// or otherwise the client-side DOCKER_BUILDKIT environment variable
+func (cli *DockerCli) BuildKitEnabled() (bool, error) {
+	if cli.buildkitEnabled == nil {
+		bke := cli.ServerInfo().BuildkitVersion == types.BuilderBuildKit
+		if buildkitEnv := os.Getenv("DOCKER_BUILDKIT"); buildkitEnv != "" {
+			enableBuildkit, err := strconv.ParseBool(buildkitEnv)
+			if err != nil {
+				return false, errors.Wrap(err, "DOCKER_BUILDKIT environment variable expects boolean value")
+			}
+			bke = enableBuildkit
+		}
+		cli.buildkitEnabled = &bke
+	}
+	return *cli.buildkitEnabled, nil
+}
+
 // ManifestStore returns a store for local manifests
 func (cli *DockerCli) ManifestStore() manifeststore.Store {
 	// TODO: support override default location from config file

cli/command/image/build.go

@@ -13,7 +13,6 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
-	"strconv"
 	"strings"
 
 	"github.com/docker/cli/cli"
@@ -159,9 +158,11 @@ func NewBuildCommand(dockerCli command.Cli) *cobra.Command {
 
 	flags.StringArrayVar(&options.secrets, "secret", []string{}, "Secret file to expose to the build (only if BuildKit enabled): id=mysecret,src=/local/secret")
 	flags.SetAnnotation("secret", "version", []string{"1.39"})
+	flags.SetAnnotation("secret", "buildkit", nil)
 
 	flags.StringArrayVar(&options.ssh, "ssh", []string{}, "SSH agent socket or keys to expose to the build (only if BuildKit enabled) (format: default|<id>[=<socket>|<key>[,<key>]])")
 	flags.SetAnnotation("ssh", "version", []string{"1.39"})
+	flags.SetAnnotation("ssh", "buildkit", nil)
 	return cmd
 }
 
@@ -183,22 +184,17 @@ func (out *lastProgressOutput) WriteProgress(prog progress.Progress) error {
 
 // nolint: gocyclo
 func runBuild(dockerCli command.Cli, options buildOptions) error {
-	if buildkitEnv := os.Getenv("DOCKER_BUILDKIT"); buildkitEnv != "" {
-		enableBuildkit, err := strconv.ParseBool(buildkitEnv)
-		if err != nil {
-			return errors.Wrap(err, "DOCKER_BUILDKIT environment variable expects boolean value")
-		}
-		if enableBuildkit {
-			return runBuildBuildKit(dockerCli, options)
-		}
-	} else if dockerCli.ServerInfo().BuildkitVersion == types.BuilderBuildKit {
+	buildkitEnabled, err := dockerCli.BuildKitEnabled()
+	if err != nil {
+		return err
+	}
+	if buildkitEnabled {
 		return runBuildBuildKit(dockerCli, options)
 	}
 
 	var (
 		buildCtx      io.ReadCloser
 		dockerfileCtx io.ReadCloser
-		err           error
 		contextDir    string
 		tempDir       string
 		relDockerfile string

cmd/docker/docker.go

@@ -100,8 +100,10 @@ func setHelpFunc(dockerCli *command.DockerCli, cmd *cobra.Command, flags *pflag.
 			ccmd.Println(err)
 			return
 		}
-
-		hideUnsupportedFeatures(ccmd, dockerCli)
+		if err := hideUnsupportedFeatures(ccmd, dockerCli); err != nil {
+			ccmd.Println(err)
+			return
+		}
 		defaultHelpFunc(ccmd, args)
 	})
 }
@@ -215,6 +217,7 @@ type versionDetails interface {
 	Client() client.APIClient
 	ClientInfo() command.ClientInfo
 	ServerInfo() command.ServerInfo
+	BuildKitEnabled() (bool, error)
 }
 
 func hideFeatureFlag(f *pflag.Flag, hasFeature bool, annotation string) {
@@ -235,15 +238,20 @@ func hideFeatureSubCommand(subcmd *cobra.Command, hasFeature bool, annotation st
 	}
 }
 
-func hideUnsupportedFeatures(cmd *cobra.Command, details versionDetails) {
+func hideUnsupportedFeatures(cmd *cobra.Command, details versionDetails) error {
 	clientVersion := details.Client().ClientVersion()
 	osType := details.ServerInfo().OSType
 	hasExperimental := details.ServerInfo().HasExperimental
 	hasExperimentalCLI := details.ClientInfo().HasExperimental
+	hasBuildKit, err := details.BuildKitEnabled()
+	if err != nil {
+		return err
+	}
 
 	cmd.Flags().VisitAll(func(f *pflag.Flag) {
 		hideFeatureFlag(f, hasExperimental, "experimental")
 		hideFeatureFlag(f, hasExperimentalCLI, "experimentalCLI")
+		hideFeatureFlag(f, hasBuildKit, "buildkit")
 		// hide flags not supported by the server
 		if !isOSTypeSupported(f, osType) || !isVersionSupported(f, clientVersion) {
 			f.Hidden = true
@@ -259,6 +267,7 @@ func hideUnsupportedFeatures(cmd *cobra.Command, details versionDetails) {
 	for _, subcmd := range cmd.Commands() {
 		hideFeatureSubCommand(subcmd, hasExperimental, "experimental")
 		hideFeatureSubCommand(subcmd, hasExperimentalCLI, "experimentalCLI")
+		hideFeatureSubCommand(subcmd, hasBuildKit, "buildkit")
 		// hide subcommands not supported by the server
 		if subcmdVersion, ok := subcmd.Annotations["version"]; ok && versions.LessThan(clientVersion, subcmdVersion) {
 			subcmd.Hidden = true
@@ -267,6 +276,7 @@ func hideUnsupportedFeatures(cmd *cobra.Command, details versionDetails) {
 			subcmd.Hidden = true
 		}
 	}
+	return nil
 }
 
 // Checks if a command or one of its ancestors is in the list
@@ -313,6 +323,7 @@ func areFlagsSupported(cmd *cobra.Command, details versionDetails) error {
 			if _, ok := f.Annotations["experimentalCLI"]; ok && !hasExperimentalCLI {
 				errs = append(errs, fmt.Sprintf("\"--%s\" is on a Docker cli with experimental cli features enabled", f.Name))
 			}
+			// buildkit-specific flags are noop when buildkit is not enabled, so we do not add an error in that case
 		}
 	})
 	if len(errs) > 0 {