Preallocate a slice

When we already know the resulting slice size but still need/want to use
append, it makes sense to preallocate the slice by using make with the
capacity argument.

This commit is part of series fixing issues reported by prealloc linter
from golangci-lint v2.8.0.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

cmd/podman/containers/ps.go

@@ -145,7 +145,7 @@ func jsonOut(responses []entities.ListContainer) error {
 		entities.ListContainer
 		Created int64
 	}
-	r := make([]jsonFormat, 0)
+	r := make([]jsonFormat, 0, len(responses))
 	for _, con := range responses {
 		con.CreatedAt = units.HumanDuration(time.Since(con.Created)) + " ago"
 		con.Status = psReporter{con}.Status()

cmd/podman/machine/machine.go

@@ -103,8 +103,9 @@ func AutocompleteMachine(cmd *cobra.Command, args []string, toComplete string) (
 }
 
 func autocompleteMachineProvider(_ *cobra.Command, _ []string, _ string) ([]string, cobra.ShellCompDirective) {
-	suggestions := make([]string, 0)
-	for _, p := range provider2.GetAll() {
+	providers := provider2.GetAll()
+	suggestions := make([]string, 0, len(providers))
+	for _, p := range providers {
 		suggestions = append(suggestions, p.VMType().String())
 	}
 	return suggestions, cobra.ShellCompDirectiveNoFileComp

cmd/quadlet/main.go

@@ -135,9 +135,8 @@ func loadUnitDropins(unit *parser.UnitFile, sourcePaths []string) error {
 		prevError = err
 	}
 
-	dropinDirs := []string{}
 	unitDropinPaths := unit.GetUnitDropinPaths()
-
+	dropinDirs := make([]string, 0, len(unitDropinPaths))
 	for _, dropinPath := range unitDropinPaths {
 		for _, sourcePath := range sourcePaths {
 			dropinDirs = append(dropinDirs, path.Join(sourcePath, dropinPath))

libpod/container.go

@@ -464,7 +464,7 @@ func (c *Container) StaticDir() string {
 // The name of each is guaranteed to point to a valid libpod Volume present in
 // the state.
 func (c *Container) NamedVolumes() []*ContainerNamedVolume {
-	volumes := []*ContainerNamedVolume{}
+	volumes := make([]*ContainerNamedVolume, 0, len(c.config.NamedVolumes))
 	for _, vol := range c.config.NamedVolumes {
 		newVol := new(ContainerNamedVolume)
 		newVol.Name = vol.Name

libpod/kube.go

@@ -441,7 +441,7 @@ type YAMLContainer struct {
 
 // ConvertV1PodToYAMLPod takes k8s API core Pod and returns a pointer to YAMLPod
 func ConvertV1PodToYAMLPod(pod *v1.Pod) *YAMLPod {
-	cs := []*YAMLContainer{}
+	cs := make([]*YAMLContainer, 0, len(pod.Spec.Containers))
 	for _, cc := range pod.Spec.Containers {
 		var res *v1.ResourceRequirements
 		if len(cc.Resources.Limits) > 0 || len(cc.Resources.Requests) > 0 {

libpod/oci_conmon_linux.go

@@ -263,7 +263,7 @@ func GetLimits(resource *spec.LinuxResources) (runcconfig.Resources, error) {
 	final.Devices = devs
 
 	// HugepageLimits
-	pageLimits := []*runcconfig.HugepageLimit{}
+	pageLimits := make([]*runcconfig.HugepageLimit, 0, len(resource.HugepageLimits))
 	for _, entry := range resource.HugepageLimits {
 		pageLimits = append(pageLimits, &runcconfig.HugepageLimit{
 			Pagesize: entry.Pagesize,

pkg/api/handlers/utils/containers.go

@@ -163,7 +163,7 @@ func createContainerWaitFn(ctx context.Context, containerName string, interval t
 	var containerEngine entities.ContainerEngine = &abi.ContainerEngine{Libpod: runtime}
 
 	return func(conditions ...define.ContainerStatus) (int32, error) {
-		var rawConditions []string
+		rawConditions := make([]string, 0, len(conditions))
 		for _, con := range conditions {
 			rawConditions = append(rawConditions, con.String())
 		}

pkg/domain/filters/containers.go

@@ -37,7 +37,7 @@ func GenerateContainerFilterFuncs(filter string, filterValues []string, r *libpo
 	case "name":
 		// we only have to match one name
 		return func(c *libpod.Container) bool {
-			var filters []string
+			filters := make([]string, 0, len(filterValues))
 			for _, f := range filterValues {
 				filters = append(filters, strings.ReplaceAll(f, "/", ""))
 			}

pkg/domain/infra/abi/volumes.go

@@ -210,7 +210,7 @@ func (ic *ContainerEngine) VolumeMounted(_ context.Context, nameOrID string) (*e
 }
 
 func (ic *ContainerEngine) VolumeMount(_ context.Context, nameOrIDs []string) ([]*entities.VolumeMountReport, error) {
-	reports := []*entities.VolumeMountReport{}
+	reports := make([]*entities.VolumeMountReport, 0, len(nameOrIDs))
 	for _, name := range nameOrIDs {
 		report := entities.VolumeMountReport{Id: name}
 		vol, err := ic.Libpod.LookupVolume(name)
@@ -226,7 +226,7 @@ func (ic *ContainerEngine) VolumeMount(_ context.Context, nameOrIDs []string) ([
 }
 
 func (ic *ContainerEngine) VolumeUnmount(_ context.Context, nameOrIDs []string) ([]*entities.VolumeUnmountReport, error) {
-	reports := []*entities.VolumeUnmountReport{}
+	reports := make([]*entities.VolumeUnmountReport, 0, len(nameOrIDs))
 	for _, name := range nameOrIDs {
 		report := entities.VolumeUnmountReport{Id: name}
 		vol, err := ic.Libpod.LookupVolume(name)

pkg/domain/infra/tunnel/containers.go

@@ -598,7 +598,7 @@ func (ic *ContainerEngine) ContainerAttach(ctx context.Context, nameOrID string,
 }
 
 func makeExecConfig(options entities.ExecOptions) *handlers.ExecCreateConfig {
-	env := []string{}
+	env := make([]string, 0, len(options.Envs))
 	for k, v := range options.Envs {
 		env = append(env, fmt.Sprintf("%s=%s", k, v))
 	}

pkg/trust/trust.go

@@ -78,7 +78,7 @@ func getPolicyShowOutput(policyContentStruct policyContent, systemRegistriesDirP
 
 // descriptionsOfPolicyRequirements turns reqs into user-readable policy entries, with Transport/Name/Reponame coming from template, potentially looking up scope (which may be "") in registryConfigs.
 func descriptionsOfPolicyRequirements(reqs []repoContent, template Policy, registryConfigs *registryConfiguration, scope string, idReader gpgIDReader) []*Policy {
-	res := []*Policy{}
+	res := make([]*Policy, 0, len(reqs))
 
 	var lookasidePath string
 	registryNamespace := registriesDConfigurationForScope(registryConfigs, scope)

pkg/util/utils.go

@@ -612,13 +612,13 @@ func getAvailableIDRanges(fullRanges, usedRanges [][2]int) (availableRanges [][2
 // multirange of unassigned subordinated ids.
 func getAvailableIDRangesFromMappings(idmap []idtools.IDMap, parentMapping []ruser.IDMap) (availableRanges [][2]int) {
 	// Get all subordinated ids from parentMapping:
-	fullRanges := [][2]int{} // {Multirange: [start, end), [start, end), ...}
+	fullRanges := make([][2]int, 0, len(parentMapping)) // {Multirange: [start, end), [start, end), ...}
 	for _, mapPiece := range parentMapping {
 		fullRanges = append(fullRanges, [2]int{int(mapPiece.ID), int(mapPiece.ID + mapPiece.Count)})
 	}
 
 	// Get the ids already mapped:
-	usedRanges := [][2]int{}
+	usedRanges := make([][2]int, 0, len(idmap))
 	for _, mapPiece := range idmap {
 		usedRanges = append(usedRanges, [2]int{mapPiece.HostID, mapPiece.HostID + mapPiece.Size})
 	}