ls: format opt

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

builder/builder.go

@@ -2,9 +2,12 @@ package builder
 
 import (
 	"context"
+	"encoding/json"
 	"os"
 	"sort"
+	"strings"
 	"sync"
+	"time"
 
 	"github.com/docker/buildx/driver"
 	"github.com/docker/buildx/store"
@@ -247,6 +250,28 @@ func (b *Builder) Factory(ctx context.Context, dialMeta map[string][]string) (_
 	return b.driverFactory.Factory, err
 }
 
+func (b *Builder) MarshalJSON() ([]byte, error) {
+	var berr string
+	if b.err != nil {
+		berr = strings.TrimSpace(b.err.Error())
+	}
+	return json.Marshal(struct {
+		Name         string
+		Driver       string
+		LastActivity time.Time `json:",omitempty"`
+		Dynamic      bool
+		Nodes        []Node
+		Err          string `json:",omitempty"`
+	}{
+		Name:         b.Name,
+		Driver:       b.Driver,
+		LastActivity: b.LastActivity,
+		Dynamic:      b.Dynamic,
+		Nodes:        b.nodes,
+		Err:          berr,
+	})
+}
+
 // GetBuilders returns all builders
 func GetBuilders(dockerCli command.Cli, txn *store.Txn) ([]*Builder, error) {
 	storeng, err := txn.List()