From 5479df79c7859d5a09f42c22ddb5fa3e56ceeb7c Mon Sep 17 00:00:00 2001
From: Alexandre Beslic <alexandre.beslic@gmail.com>
Date: Fri, 5 Aug 2016 15:51:32 -0700
Subject: [PATCH] swarm: improve cli output on node promote/demote for
 unchanged role

As of now promoting (or demoting) a node that has its role
left unchanged will always print a successful message.

This PR fixes the issue by matching the behavior on swarmkit's
swarmctl command and printing a message when desired role is
the current role of the node.

As a result this also avoids calling update when it is not
necessary.

Signed-off-by: Alexandre Beslic <alexandre.beslic@gmail.com>
---
 api/client/node/demote.go  | 4 ++++
 api/client/node/promote.go | 4 ++++
 api/client/node/update.go  | 8 ++++++++
 3 files changed, 16 insertions(+)

diff --git a/api/client/node/demote.go b/api/client/node/demote.go
index 3819b1a399..6acf5c3eb2 100644
--- a/api/client/node/demote.go
+++ b/api/client/node/demote.go
@@ -22,6 +22,10 @@ func newDemoteCommand(dockerCli *client.DockerCli) *cobra.Command {
 
 func runDemote(dockerCli *client.DockerCli, nodes []string) error {
 	demote := func(node *swarm.Node) error {
+		if node.Spec.Role == swarm.NodeRoleWorker {
+			fmt.Fprintf(dockerCli.Out(), "Node %s is already a worker.\n", node.ID)
+			return errNoRoleChange
+		}
 		node.Spec.Role = swarm.NodeRoleWorker
 		return nil
 	}
diff --git a/api/client/node/promote.go b/api/client/node/promote.go
index 39e284f937..9bfc4a277f 100644
--- a/api/client/node/promote.go
+++ b/api/client/node/promote.go
@@ -22,6 +22,10 @@ func newPromoteCommand(dockerCli *client.DockerCli) *cobra.Command {
 
 func runPromote(dockerCli *client.DockerCli, nodes []string) error {
 	promote := func(node *swarm.Node) error {
+		if node.Spec.Role == swarm.NodeRoleManager {
+			fmt.Fprintf(dockerCli.Out(), "Node %s is already a manager.\n", node.ID)
+			return errNoRoleChange
+		}
 		node.Spec.Role = swarm.NodeRoleManager
 		return nil
 	}
diff --git a/api/client/node/update.go b/api/client/node/update.go
index 1d070dd536..9437853ca4 100644
--- a/api/client/node/update.go
+++ b/api/client/node/update.go
@@ -1,6 +1,7 @@
 package node
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/docker/docker/api/client"
@@ -13,6 +14,10 @@ import (
 	"golang.org/x/net/context"
 )
 
+var (
+	errNoRoleChange = errors.New("role was already set to the requested value")
+)
+
 func newUpdateCommand(dockerCli *client.DockerCli) *cobra.Command {
 	nodeOpts := newNodeOptions()
 
@@ -53,6 +58,9 @@ func updateNodes(dockerCli *client.DockerCli, nodes []string, mergeNode func(nod
 
 		err = mergeNode(&node)
 		if err != nil {
+			if err == errNoRoleChange {
+				continue
+			}
 			return err
 		}
 		err = client.NodeUpdate(ctx, node.ID, node.Version, node.Spec)