builder: fix default docker context behavior

builder/builder.go

@@ -97,9 +97,6 @@ func New(dockerCli command.Cli, opts ...Option) (_ *Builder, err error) {
 			return nil, err
 		}
 	}
-	if b.NodeGroup.Name == "default" && len(b.NodeGroup.Nodes) == 1 {
-		b.NodeGroup.Name = b.NodeGroup.Nodes[0].Endpoint
-	}
 	if b.opts.validate {
 		if err = b.Validate(); err != nil {
 			return nil, err
@@ -111,16 +108,16 @@ func New(dockerCli command.Cli, opts ...Option) (_ *Builder, err error) {
 
 // Validate validates builder context
 func (b *Builder) Validate() error {
-	if b.NodeGroup.Name == "default" && b.NodeGroup.Name != b.opts.dockerCli.CurrentContext() {
-		return errors.Errorf("use `docker --context=default buildx` to switch to default context")
-	}
-	list, err := b.opts.dockerCli.ContextStore().List()
-	if err != nil {
-		return err
-	}
-	for _, l := range list {
-		if l.Name == b.NodeGroup.Name && b.NodeGroup.Name != "default" {
-			return errors.Errorf("use `docker --context=%s buildx` to switch to context %q", b.NodeGroup.Name, b.NodeGroup.Name)
+	if b.NodeGroup.DockerContext {
+		list, err := b.opts.dockerCli.ContextStore().List()
+		if err != nil {
+			return err
+		}
+		currentContext := b.opts.dockerCli.CurrentContext()
+		for _, l := range list {
+			if l.Name == b.Name && l.Name != currentContext {
+				return errors.Errorf("use `docker --context=%s buildx` to switch to context %q", l.Name, l.Name)
+			}
 		}
 	}
 	return nil

store/nodegroup.go

@@ -12,10 +12,11 @@ import (
 )
 
 type NodeGroup struct {
-	Name    string
-	Driver  string
-	Nodes   []Node
-	Dynamic bool
+	Name          string
+	Driver        string
+	Nodes         []Node
+	Dynamic       bool
+	DockerContext bool
 }
 
 type Node struct {

store/storeutil/storeutil.go

@@ -79,24 +79,21 @@ func GetNodeGroup(txn *store.Txn, dockerCli command.Cli, name string) (*store.No
 		return ng, nil
 	}
 
-	if name == "default" {
-		name = dockerCli.CurrentContext()
-	}
-
 	list, err := dockerCli.ContextStore().List()
 	if err != nil {
 		return nil, err
 	}
 	for _, l := range list {
 		if l.Name == name {
 			return &store.NodeGroup{
-				Name: "default",
+				Name: name,
 				Nodes: []store.Node{
 					{
-						Name:     "default",
+						Name:     name,
 						Endpoint: name,
 					},
 				},
+				DockerContext: true,
 			}, nil
 		}
 	}