fix(load-balancer): show message if none of --server, --label-selecto…

…r or --ip is set (#849)

Previously, if none of these flags were provided, only the error
`--server, --label-selector, and --ip are mutually exclusive` would
show, which is not wrong but doesn't include that exactly one is
required.

We could also use `cmd.MarkFlagsOneRequired()` and
`cmd.MarkFlagsMutuallyExclusive()` but the errors are not very pretty.

internal/cmd/loadbalancer/add_target.go

@@ -46,6 +46,9 @@ var AddTargetCmd = base.Cmd{
 		labelSelector, _ := cmd.Flags().GetString("label-selector")
 		ipAddr, _ := cmd.Flags().GetString("ip")
 
+		if !util.AnySet(serverIDOrName, labelSelector, ipAddr) {
+			return fmt.Errorf("specify one of --server, --label-selector, or --ip")
+		}
 		if !util.ExactlyOneSet(serverIDOrName, labelSelector, ipAddr) {
 			return fmt.Errorf("--server, --label-selector, and --ip are mutually exclusive")
 		}

internal/cmd/loadbalancer/remove_target.go

@@ -54,6 +54,9 @@ var RemoveTargetCmd = base.Cmd{
 			return fmt.Errorf("Load Balancer not found: %s", idOrName)
 		}
 
+		if !util.AnySet(serverIDOrName, labelSelector, ipAddr) {
+			return fmt.Errorf("specify one of --server, --label-selector, or --ip")
+		}
 		if !util.ExactlyOneSet(serverIDOrName, labelSelector, ipAddr) {
 			return fmt.Errorf("--server, --label-selector, and --ip are mutually exclusive")
 		}

internal/cmd/util/util.go

@@ -90,6 +90,15 @@ func ChainRunE(fns ...func(cmd *cobra.Command, args []string) error) func(cmd *c
 	}
 }
 
+func AnySet(ss ...string) bool {
+	for _, s := range ss {
+		if s != "" {
+			return true
+		}
+	}
+	return false
+}
+
 func ExactlyOneSet(s string, ss ...string) bool {
 	set := s != ""
 	for _, s := range ss {