build: add completion to list context folders

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

commands/build.go

@@ -22,7 +22,6 @@ import (
 	"github.com/docker/buildx/store"
 	"github.com/docker/buildx/store/storeutil"
 	"github.com/docker/buildx/util/buildflags"
-	"github.com/docker/buildx/util/cobrautil"
 	"github.com/docker/buildx/util/ioset"
 	"github.com/docker/buildx/util/progress"
 	"github.com/docker/buildx/util/tracing"
@@ -236,7 +235,9 @@ func buildCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 			}
 			return runBuild(dockerCli, options)
 		},
-		ValidArgsFunction: cobrautil.NoCompletion,
+		ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+			return nil, cobra.ShellCompDirectiveFilterDirs
+		},
 	}
 
 	var platformsDefault []string