fix: map and slice create style

cmd/kubeadm/app/phases/upgrade/compute.go

@@ -77,7 +77,7 @@ func GetAvailableUpgrades(versionGetterImpl VersionGetter, experimentalUpgradesA
 	printer.Printf("[upgrade] Fetching available versions to upgrade to\n")
 
 	// Collect the upgrades kubeadm can do in this list
-	upgrades := []Upgrade{}
+	var upgrades []Upgrade
 
 	// Get the cluster version
 	clusterVersionStr, clusterVersion, err := versionGetterImpl.ClusterVersion()

cmd/kubeadm/app/phases/upgrade/compute_test.go

@@ -137,7 +137,7 @@ func TestGetAvailableUpgrades(t *testing.T) {
 				stableVersion:      v1Y0.String(),
 			},
 			beforeDNSVersion:  fakeCurrentCoreDNSVersion,
-			expectedUpgrades:  []Upgrade{},
+			expectedUpgrades:  nil,
 			allowExperimental: false,
 			errExpected:       false,
 		},
@@ -342,7 +342,7 @@ func TestGetAvailableUpgrades(t *testing.T) {
 				latestVersion:      v1Z0alpha2.String(),
 			},
 			beforeDNSVersion:  fakeCurrentCoreDNSVersion,
-			expectedUpgrades:  []Upgrade{},
+			expectedUpgrades:  nil,
 			allowExperimental: true,
 			errExpected:       false,
 		},

cmd/kubeadm/app/phases/upgrade/health.go

@@ -226,7 +226,7 @@ func controlPlaneNodesReady(client clientset.Interface, _ *kubeadmapi.ClusterCon
 
 // staticPodManifestHealth makes sure the required static pods are presents
 func staticPodManifestHealth(_ clientset.Interface, _ *kubeadmapi.ClusterConfiguration) error {
-	nonExistentManifests := []string{}
+	var nonExistentManifests []string
 	for _, component := range constants.ControlPlaneComponents {
 		manifestFile := constants.GetStaticPodFilepath(component, constants.GetStaticPodDirectory())
 		if _, err := os.Stat(manifestFile); os.IsNotExist(err) {
@@ -241,7 +241,7 @@ func staticPodManifestHealth(_ clientset.Interface, _ *kubeadmapi.ClusterConfigu
 
 // getNotReadyNodes returns a string slice of nodes in the cluster that are NotReady
 func getNotReadyNodes(nodes []v1.Node) []string {
-	notReadyNodes := []string{}
+	var notReadyNodes []string
 	for _, node := range nodes {
 		for _, condition := range node.Status.Conditions {
 			if condition.Type == v1.NodeReady && condition.Status != v1.ConditionTrue {

cmd/kubeadm/app/phases/upgrade/policy.go

@@ -169,7 +169,7 @@ func detectUnstableVersionError(newK8sVersion *version.Version, newK8sVersionStr
 
 // detectTooOldKubelets errors out if the kubelet versions are so old that an unsupported skew would happen if the cluster was upgraded
 func detectTooOldKubelets(newK8sVersion *version.Version, kubeletVersions map[string]uint16) error {
-	tooOldKubeletVersions := []string{}
+	var tooOldKubeletVersions []string
 	for versionStr := range kubeletVersions {
 
 		kubeletVersion, err := version.ParseSemantic(versionStr)

cmd/kubeadm/app/phases/upgrade/postupgrade.go

@@ -48,7 +48,7 @@ import (
 // PerformPostUpgradeTasks runs nearly the same functions as 'kubeadm init' would do
 // Note that the mark-control-plane phase is left out, not needed, and no token is created as that doesn't belong to the upgrade
 func PerformPostUpgradeTasks(client clientset.Interface, cfg *kubeadmapi.InitConfiguration, patchesDir string, dryRun bool, out io.Writer) error {
-	errs := []error{}
+	var errs []error
 
 	// Upload currently used configuration to the cluster
 	// Note: This is done right in the beginning of cluster initialization; as we might want to make other phases
@@ -191,7 +191,7 @@ func GetKubeletDir(dryRun bool) (string, error) {
 
 // moveFiles moves files from one directory to another.
 func moveFiles(files map[string]string) error {
-	filesToRecover := map[string]string{}
+	filesToRecover := make(map[string]string, len(files))
 	for from, to := range files {
 		if err := os.Rename(from, to); err != nil {
 			return rollbackFiles(filesToRecover, err)

cmd/kubeadm/app/phases/upgrade/versiongetter.go

@@ -21,7 +21,7 @@ import (
 
 	"github.com/pkg/errors"
 
-	"k8s.io/api/core/v1"
+	v1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	versionutil "k8s.io/apimachinery/pkg/util/version"
 	clientset "k8s.io/client-go/kubernetes"
@@ -105,7 +105,7 @@ func (g *KubeVersionGetter) KubeletVersions() (map[string]uint16, error) {
 
 // computeKubeletVersions returns a string-int map that describes how many nodes are of a specific version
 func computeKubeletVersions(nodes []v1.Node) map[string]uint16 {
-	kubeletVersions := map[string]uint16{}
+	kubeletVersions := make(map[string]uint16)
 	for _, node := range nodes {
 		kver := node.Status.NodeInfo.KubeletVersion
 		if _, found := kubeletVersions[kver]; !found {