docker build: check experimental --platform on pre-run

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit a88a1bea23)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/image/build.go

@@ -115,6 +115,25 @@ func NewBuildCommand(dockerCli command.Cli) *cobra.Command {
 		},
 	}
 
+	// Wrap the global pre-run to handle non-BuildKit use of the --platform flag.
+	//
+	// We're doing it here so that we're only contacting the daemon when actually
+	// running the command, and not during initialization.
+	// TODO remove this hack once we no longer support the experimental use of --platform
+	rootFn := cmd.Root().PersistentPreRunE
+	cmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
+		if ok, _ := command.BuildKitEnabled(dockerCli.ServerInfo()); !ok {
+			f := cmd.Flag("platform")
+			delete(f.Annotations, "buildkit")
+			f.Annotations["version"] = []string{"1.32"}
+			f.Annotations["experimental"] = nil
+		}
+		if rootFn != nil {
+			return rootFn(cmd, args)
+		}
+		return nil
+	}
+
 	flags := cmd.Flags()
 
 	flags.VarP(&options.tags, "tag", "t", "Name and optionally a tag in the 'name:tag' format")
@@ -163,14 +182,8 @@ func NewBuildCommand(dockerCli command.Cli) *cobra.Command {
 	command.AddTrustVerificationFlags(flags, &options.untrusted, dockerCli.ContentTrustEnabled())
 
 	flags.StringVar(&options.platform, "platform", os.Getenv("DOCKER_DEFAULT_PLATFORM"), "Set platform if server is multi-platform capable")
-	// Platform is not experimental when BuildKit is used
+	flags.SetAnnotation("platform", "version", []string{"1.38"})
-	buildkitEnabled, err := command.BuildKitEnabled(dockerCli.ServerInfo())
+	flags.SetAnnotation("platform", "buildkit", nil)
-	if err == nil && buildkitEnabled {
-		flags.SetAnnotation("platform", "version", []string{"1.38"})
-	} else {
-		flags.SetAnnotation("platform", "version", []string{"1.32"})
-		flags.SetAnnotation("platform", "experimental", nil)
-	}
 
 	flags.BoolVar(&options.squash, "squash", false, "Squash newly built layers into a single new layer")
 	flags.SetAnnotation("squash", "experimental", nil)

cli/command/image/build_test.go

@@ -20,11 +20,13 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"github.com/moby/buildkit/session/secrets/secretsprovider"
 	"gotest.tools/v3/assert"
+	"gotest.tools/v3/env"
 	"gotest.tools/v3/fs"
 	"gotest.tools/v3/skip"
 )
 
 func TestRunBuildDockerfileFromStdinWithCompress(t *testing.T) {
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
 	buffer := new(bytes.Buffer)
 	fakeBuild := newFakeBuild()
 	fakeImageBuild := func(ctx context.Context, context io.Reader, options types.ImageBuildOptions) (types.ImageBuildResponse, error) {
@@ -60,6 +62,7 @@ func TestRunBuildDockerfileFromStdinWithCompress(t *testing.T) {
 }
 
 func TestRunBuildResetsUidAndGidInContext(t *testing.T) {
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
 	skip.If(t, os.Getuid() != 0, "root is required to chown files")
 	fakeBuild := newFakeBuild()
 	cli := test.NewFakeCli(&fakeClient{imageBuildFunc: fakeBuild.build})
@@ -90,6 +93,7 @@ func TestRunBuildResetsUidAndGidInContext(t *testing.T) {
 }
 
 func TestRunBuildDockerfileOutsideContext(t *testing.T) {
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
 	dir := fs.NewDir(t, t.Name(),
 		fs.WithFile("data", "data file"))
 	defer dir.Remove()
@@ -122,7 +126,8 @@ COPY data /data
 // TODO: test "context selection" logic directly when runBuild is refactored
 // to support testing (ex: docker/cli#294)
 func TestRunBuildFromGitHubSpecialCase(t *testing.T) {
-	cmd := NewBuildCommand(test.NewFakeCli(nil))
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
+	cmd := NewBuildCommand(test.NewFakeCli(&fakeClient{}))
 	// Clone a small repo that exists so git doesn't prompt for credentials
 	cmd.SetArgs([]string{"github.com/docker/for-win"})
 	cmd.SetOutput(ioutil.Discard)
@@ -135,6 +140,7 @@ func TestRunBuildFromGitHubSpecialCase(t *testing.T) {
 // starting with `github.com` takes precedence over the `github.com` special
 // case.
 func TestRunBuildFromLocalGitHubDir(t *testing.T) {
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
 	tmpDir, err := ioutil.TempDir("", "docker-build-from-local-dir-")
 	assert.NilError(t, err)
 	defer os.RemoveAll(tmpDir)
@@ -154,6 +160,7 @@ func TestRunBuildFromLocalGitHubDir(t *testing.T) {
 }
 
 func TestRunBuildWithSymlinkedContext(t *testing.T) {
+	defer env.Patch(t, "DOCKER_BUILDKIT", "0")()
 	dockerfile := `
 FROM alpine:3.6
 RUN echo hello world