cmd/utils: reduce nesting levels a bit

cmd/utils/flags.go

@@ -929,31 +929,41 @@ func setEthash(ctx *cli.Context, cfg *eth.Config) {
 	}
 }
 
+// checkExclusive verifies that only a single isntance of the provided flags was
+// set by the user. Each flag might optionally be followed by a string type to
+// specialize it further.
 func checkExclusive(ctx *cli.Context, args ...interface{}) {
 	set := make([]string, 0, 1)
-	for i, arg := range args {
-		if flag, ok := arg.(cli.Flag); ok {
-			if ctx.GlobalIsSet(flag.GetName()) {
-				// Check if next arg extends current
-				if len(args) > i+1 {
-					switch option := args[i+1].(type) {
-					case cli.Flag:
-						set = append(set, `"--`+flag.GetName()+`"`)
-					case string:
-						if ctx.GlobalString(flag.GetName()) == option {
-							set = append(set, `"--`+flag.GetName()+` `+option+`"`)
-						}
-					default:
-						Fatalf("Received wrong type in checkExclusive")
-					}
-				} else {
-					set = append(set, `"--`+flag.GetName()+`"`)
+	for i := 0; i < len(args); i++ {
+		// Make sure the next argument is a flag and skip if not set
+		flag, ok := args[i].(cli.Flag)
+		if !ok {
+			panic(fmt.Sprintf("invalid argument, not cli.Flag type: %T", args[i]))
+		}
+		// Check if next arg extends current and expand its name if so
+		name := flag.GetName()
+
+		if i+1 < len(args) {
+			switch option := args[i+1].(type) {
+			case string:
+				// Extended flag, expand the name and shift the arguments
+				if ctx.GlobalString(flag.GetName()) == option {
+					name += "=" + option
 				}
+				i++
+
+			case cli.Flag:
+			default:
+				panic(fmt.Sprintf("invalid argument, not cli.Flag or string extension: %T", args[i+1]))
 			}
 		}
+		// Mark the flag if it's set
+		if ctx.GlobalIsSet(flag.GetName()) {
+			set = append(set, "--"+name)
+		}
 	}
 	if len(set) > 1 {
-		Fatalf("flags %v can't be used at the same time", strings.Join(set, ", "))
+		Fatalf("Flags %v can't be used at the same time", strings.Join(set, ", "))
 	}
 }