fix: always add missing slashes to link names

previously, this was only done when marking  dependant containers
for restart. but since the names should ALWAYS start with a slash,
this check could be performed every time the container is iterated.
the only downside to this is that it's less performant (as it needs to
copy the strings instead of just having the slices point to the same
source string), but it should not be noticable.

internal/actions/update.go

@@ -2,7 +2,6 @@ package actions
 
 import (
 	"errors"
-	"strings"
 
 	"github.com/containrrr/watchtower/internal/util"
 	"github.com/containrrr/watchtower/pkg/container"
@@ -260,10 +259,6 @@ func UpdateImplicitRestart(containers []container.Container) {
 // container marked for restart
 func linkedContainerMarkedForRestart(links []string, containers []container.Container) string {
 	for _, linkName := range links {
-		// Since the container names need to start with '/', let's prepend it if it's missing
-		if !strings.HasPrefix(linkName, "/") {
-			linkName = "/" + linkName
-		}
 		for _, candidate := range containers {
 			if candidate.Name() == linkName && candidate.ToRestart() {
 				return linkName

pkg/container/container.go

@@ -160,7 +160,14 @@ func (c Container) Links() []string {
 	dependsOnLabelValue := c.getLabelValueOrEmpty(dependsOnLabel)
 
 	if dependsOnLabelValue != "" {
-		links := strings.Split(dependsOnLabelValue, ",")
+		for _, link := range strings.Split(dependsOnLabelValue, ",") {
+			// Since the container names need to start with '/', let's prepend it if it's missing
+			if !strings.HasPrefix(link, "/") {
+				link = "/" + link
+			}
+			links = append(links, link)
+		}
+
 		return links
 	}
 

pkg/container/container_test.go

@@ -178,14 +178,21 @@ var _ = Describe("the container", func() {
 						"com.centurylinklabs.watchtower.depends-on": "postgres",
 					}))
 					links := c.Links()
-					Expect(links).To(SatisfyAll(ContainElement("postgres"), HaveLen(1)))
+					Expect(links).To(SatisfyAll(ContainElement("/postgres"), HaveLen(1)))
 				})
 				It("should fetch depending containers if there are many", func() {
 					c = MockContainer(WithLabels(map[string]string{
 						"com.centurylinklabs.watchtower.depends-on": "postgres,redis",
 					}))
 					links := c.Links()
-					Expect(links).To(SatisfyAll(ContainElement("postgres"), ContainElement("redis"), HaveLen(2)))
+					Expect(links).To(SatisfyAll(ContainElement("/postgres"), ContainElement("/redis"), HaveLen(2)))
+				})
+				It("should only add slashes to names when they are missing", func() {
+					c = MockContainer(WithLabels(map[string]string{
+						"com.centurylinklabs.watchtower.depends-on": "/postgres,redis",
+					}))
+					links := c.Links()
+					Expect(links).To(SatisfyAll(ContainElement("/postgres"), ContainElement("/redis")))
 				})
 				It("should fetch depending containers if label is blank", func() {
 					c = MockContainer(WithLabels(map[string]string{