What causes "%s must be followed by an argument" in go-delve/delve?

Append the filter kind after the flag, e.g. 'goroutines -with label "foo"'.

%s must be followed by an argument

Error message

%s must be followed by an argument

What it means

readGoroutinesFilterKind validates the value that must follow a goroutines filter flag (like -with or -without). If the flag is the last token in the argument list, the required value is missing and this error is thrown. args[i-1] is the flag that needed a value.

Source

Thrown at service/api/command.go:126

			filters = append(filters, ListGoroutinesFilter{Kind: GoroutineWaitingOnChannel, Arg: args[i]})

		case "-exec":
			flags |= PrintGoroutinesExec
			cmd = strings.Join(args[i+1:], " ")
			i = len(args)

		case "":
			// nothing to do
		default:
			return nil, GoroutineGroupingOptions{}, 0, 0, 0, 0, "", fmt.Errorf("wrong argument: '%s'", arg)
		}
	}
	return filters, group, fgl, flags, depth, batchSize, cmd, nil
}

func readGoroutinesFilterKind(args []string, i int) (GoroutineField, error) {
	if i >= len(args) {
		return GoroutineFieldNone, fmt.Errorf("%s must be followed by an argument", args[i-1])
	}

	switch args[i] {
	case "curloc":
		return GoroutineCurrentLoc, nil
	case "userloc":
		return GoroutineUserLoc, nil
	case "goloc":
		return GoroutineGoLoc, nil
	case "startloc":
		return GoroutineStartLoc, nil
	case "label":
		return GoroutineLabel, nil
	case "running":
		return GoroutineRunning, nil
	case "user":
		return GoroutineUser, nil
	default:

View on GitHub (pinned to a23773e6c3)

Solutions

Append the filter kind after the flag, e.g. 'goroutines -with label "foo"'.
Use a valid kind: curloc, userloc, label, function, running, user, file, line.
If you intended no filter, remove the dangling flag entirely.

Example fix

// before
cmd.ProcessLine("goroutines -with")
// after
cmd.ProcessLine("goroutines -with label worker")

Defensive patterns

Strategy: validation

Validate before calling

func hasValueAfter(args []string, i int) bool { return i+1 < len(args) }
// ensure every flag that needs a kind has a following token before calling ParseGoroutineArgs

Try / catch

_, _, _, _, _, _, _, err := api.ParseGoroutineArgs(args)
if err != nil {
	log.Printf("filter flag missing value: %v", err)
}

Prevention

Never end an argument list with a bare filter flag
Check for dangling '-' tokens after shell splitting
Use quoting for values with spaces

When it happens

Trigger: Calling ParseGoroutineArgs or readGoroutinesFilter with a filter flag at the end of the argument list with no following value, e.g. 'goroutines -with label' or 'goroutines -without' (nothing after it).

Common situations: Quoting mistakes that swallow the value; forgetting the filter kind (curloc/userloc/label/function/running/user/file/line); shell splitting removing an empty quoted argument.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/f770131aa3807edf. Report an issue: GitHub.