build: use legacy builder for wcow if not opt-in with a builder compo…

…nent

Signed-off-by: CrazyMax <[email protected]>

cmd/docker/builder.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"fmt"
+	"os"
+	"strconv"
 
 	pluginmanager "github.com/docker/cli/cli-plugins/manager"
 	"github.com/docker/cli/cli/command"
@@ -39,16 +41,19 @@ func newBuilderError(warn bool, err error) error {
 }
 
 func processBuilder(dockerCli command.Cli, cmd *cobra.Command, args, osargs []string) ([]string, []string, error) {
-	var useLegacy bool
-	var useBuilder bool
+	var useLegacy, useBuilder bool
 
-	if bkExplicit, err := command.DockerBuildKitEnabled(); err != nil {
-		return nil, nil, err
-	} else if bkExplicit != nil {
-		if *bkExplicit {
-			useBuilder = true
-		} else {
+	// check DOCKER_BUILDKIT env var is present and
+	// if not assume we want to use the builder component
+	if v, ok := os.LookupEnv("DOCKER_BUILDKIT"); ok {
+		enabled, err := strconv.ParseBool(v)
+		if err != nil {
+			return args, osargs, errors.Wrap(err, "DOCKER_BUILDKIT environment variable expects boolean value")
+		}
+		if !enabled {
 			useLegacy = true
+		} else {
+			useBuilder = true
 		}
 	}
 
@@ -67,6 +72,12 @@ func processBuilder(dockerCli command.Cli, cmd *cobra.Command, args, osargs []st
 		return args, osargs, nil
 	}
 
+	// wcow build command must use the legacy builder
+	// if not opt-in through a builder component
+	if !useBuilder && dockerCli.ServerInfo().OSType == "windows" {
+		return args, osargs, nil
+	}
+
 	if useLegacy {
 		// display warning if not wcow and continue
 		if dockerCli.ServerInfo().OSType != "windows" {