Add some minor tweaks to machine readable pathway in recipe upgrade

cli/recipe/upgrade.go

@@ -28,6 +28,8 @@ type imgPin struct {
 	version tagcmp.Tag
 }
 
+// anUpgrade represents a single service upgrade (as within a recipe), and the list of tags that it can be upgraded to,
+// for serialization purposes.
 type anUpgrade struct {
 	Service     string   `json:"service"`
 	Image       string   `json:"image"`
@@ -257,14 +259,17 @@ You may invoke this command in "wizard" mode and be prompted for input:
 						}
 					}
 
+					// there is always at least the item "skip" in compatibleStrings (a list of
+					// possible upgradable tags) and at least one other tag.
+					upgradableTags := compatibleStrings[1:]
 					upgrade := anUpgrade{
 						Service:     service.Name,
 						Image:       image,
 						Tag:         tag.String(),
-						UpgradeTags: make([]string, len(compatibleStrings[1:])),
+						UpgradeTags: make([]string, len(upgradableTags)),
 					}
 
-					for n, s := range compatibleStrings[1:] {
+					for n, s := range upgradableTags {
 						var sb strings.Builder
 						if _, err := sb.WriteString(s); err != nil {
 						}
@@ -308,16 +313,16 @@ You may invoke this command in "wizard" mode and be prompted for input:
 				jsonstring, err := json.Marshal(upgradeList)
 				if err != nil {
 					logrus.Fatal(err)
-				} else {
-					fmt.Println(string(jsonstring))
 				}
 
-			} else {
-				for _, upgrade := range upgradeList {
-					logrus.Infof("can upgrade service: %s, image: %s, tag: %s ::\n", upgrade.Service, upgrade.Image, upgrade.Tag)
-					for _, utag := range upgrade.UpgradeTags {
-						logrus.Infof("    %s\n", utag)
-					}
+				fmt.Println(string(jsonstring))
+				return nil
+			}
+
+			for _, upgrade := range upgradeList {
+				logrus.Infof("can upgrade service: %s, image: %s, tag: %s ::\n", upgrade.Service, upgrade.Image, upgrade.Tag)
+				for _, utag := range upgrade.UpgradeTags {
+					logrus.Infof("    %s\n", utag)
 				}
 			}
 		}