registry: log out of Docker Hub when given docker.io

cli/command/registry/logout.go

@@ -46,7 +46,9 @@ func runLogout(ctx context.Context, dockerCLI command.Cli, serverAddress string)
 
 	var isDefaultRegistry bool
 
-	if serverAddress == "" {
+	// login stores Docker Hub creds under the index server for both an empty
+	// server and an explicit "docker.io". logout has to use the same key.
+	if serverAddress == "" || serverAddress == registry.DefaultNamespace {
 		serverAddress = registry.IndexServer
 		isDefaultRegistry = true
 	}

cli/command/registry/logout_test.go

@@ -0,0 +1,41 @@
+package registry
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+
+	"github.com/docker/cli/cli/config/configfile"
+	configtypes "github.com/docker/cli/cli/config/types"
+	"github.com/docker/cli/internal/registry"
+	"github.com/docker/cli/internal/test"
+	"gotest.tools/v3/assert"
+	is "gotest.tools/v3/assert/cmp"
+)
+
+func TestRunLogoutDockerIORemovesHubCredentials(t *testing.T) {
+	tmpDir := t.TempDir()
+	cfg := configfile.New(filepath.Join(tmpDir, "config.json"))
+	cfg.AuthConfigs = map[string]configtypes.AuthConfig{
+		registry.IndexServer: {
+			Username:      "user",
+			Password:      "pass",
+			ServerAddress: registry.IndexServer,
+		},
+		"example.com": {
+			Username:      "other",
+			Password:      "secret",
+			ServerAddress: "example.com",
+		},
+	}
+	cli := test.NewFakeCli(nil)
+	cli.SetConfigFile(cfg)
+
+	assert.NilError(t, runLogout(context.Background(), cli, "docker.io"))
+
+	_, hubOK := cfg.AuthConfigs[registry.IndexServer]
+	assert.Check(t, !hubOK)
+	_, otherOK := cfg.AuthConfigs["example.com"]
+	assert.Check(t, otherOK)
+	assert.Check(t, is.Contains(cli.OutBuffer().String(), "Removing login credentials for "+registry.IndexServer))
+}