Prevent unnecessary application of default repository (#4817)

Author: anshlykov

pkg/skaffold/docker/default_repo.go

@@ -50,16 +50,16 @@ func SubstituteDefaultRepoIntoImage(defaultRepo string, image string) (string, e
 }
 
 func replace(defaultRepo string, baseImage string) string {
+	if strings.HasPrefix(baseImage, defaultRepo) {
+		return baseImage
+	}
 	originalPrefix := prefixRegex.FindString(baseImage)
 	defaultRepoPrefix := prefixRegex.FindString(defaultRepo)
 	if originalPrefix != "" && defaultRepoPrefix != "" {
 		// prefixes match
 		if originalPrefix == defaultRepoPrefix {
 			return defaultRepo + "/" + baseImage[len(originalPrefix):]
 		}
-		if strings.HasPrefix(baseImage, defaultRepo) {
-			return baseImage
-		}
 		// prefixes don't match, concatenate and truncate
 		return truncate(defaultRepo + "/" + baseImage)
 	}

pkg/skaffold/docker/default_repo_test.go

@@ -77,6 +77,12 @@ func TestImageReplaceDefaultRepo(t *testing.T) {
 			defaultRepo:   "gcr.io/k8s-skaffold",
 			expectedImage: "gcr.io/k8s-skaffold/skaffold-example",
 		},
+		{
+			description:   "image has shared prefix with defaultRepo, but not gcr",
+			image:         "myrepo/skaffold-example",
+			defaultRepo:   "myrepo",
+			expectedImage: "myrepo/skaffold-example",
+		},
 		{
 			description:   "keep tag",
 			image:         "img:tag",