go-delve/delve · error

not enough arguments after -chan

Error message

not enough arguments after -chan

What it means

ParseGoroutineArgs parses arguments to the goroutines command. The -chan flag expects a following channel expression; when -chan is the last token (i >= len(args) after the increment), there is no filter value and parsing fails with this error. It guards ListGoroutinesFilter construction from a missing argument.

Source

Thrown at service/api/command.go:106

			var err error
			group.GroupBy, err = readGoroutinesFilterKind(args, i+1)
			if err != nil {
				return nil, GoroutineGroupingOptions{}, 0, 0, 0, 0, "", fmt.Errorf("wrong argument: '%s'", arg)
			}
			i++
			if group.GroupBy == GoroutineLabel {
				if i+1 >= len(args) {
					return nil, GoroutineGroupingOptions{}, 0, 0, 0, 0, "", fmt.Errorf("wrong argument: '%s'", arg)
				}
				group.GroupByKey = args[i+1]
				i++
			}
			batchSize = 0 // grouping only works well if run on all goroutines

		case "-chan":
			i++
			if i >= len(args) {
				return nil, GoroutineGroupingOptions{}, 0, 0, 0, 0, "", errors.New("not enough arguments after -chan")
			}
			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) {

View on GitHub (pinned to a23773e6c3)

Solutions

1. Provide a channel expression after the flag: goroutines -chan myCh
2. If the channel name comes from a variable, ensure it is non-empty before building the command
3. Use `goroutines -help` (or `help goroutines`) to review valid flags: -chan, -exec, -group, etc.

Example fix

// before
args := []string{"goroutines", "-chan"}

// after
args := []string{"goroutines", "-chan", "ch"}

# shell: fail early when the channel arg is missing
CH=${CH:?"-chan requires a channel expression"}
dlv_ex_cmd="goroutines -chan $CH"

func hasValueAfter(args []string, flag string) bool {
    for i, a := range args {
        if a == flag {
            return i+1 < len(args)
        }
    }
    return false
}

When it happens

Trigger: Invoking `goroutines -chan` with nothing after the flag, e.g. typing `goroutines -chan` at the dlv prompt or calling the RPC/API path where args ends with "-chan". Also occurs when quoting mistakes swallow the intended channel expression.

Common situations: Users forgetting the channel variable after -chan; shell scripts dropping the last argument due to an empty variable expansion (e.g. `goroutines -chan $CH` with CH unset); copy-pasting partial commands from docs.

Related errors

• expected argument after -fmt
• expected argument after -count/-len
• wrong argument: '%s'
• could not find goroutine array
• command not available

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/460088f9441310ae. Report an issue: GitHub.