go-delve/delve · error

%s %s needs to be followed by an expression

Error message

%s %s needs to be followed by an expression

What it means

readGoroutinesFilter accepts filters that require an argument (curloc, userloc, label, function, file, line). If such a filter kind is followed by no expression, this error is thrown naming both tokens. Filters like 'running' and 'user' are exempt and return early.

Source

Thrown at service/api/command.go:162

	default:
		return GoroutineFieldNone, fmt.Errorf("unrecognized argument to %s %s", args[i-1], args[i])
	}
}

func readGoroutinesFilter(args []string, pi *int) (*ListGoroutinesFilter, error) {
	r := new(ListGoroutinesFilter)
	var err error
	r.Kind, err = readGoroutinesFilterKind(args, *pi+1)
	if err != nil {
		return nil, err
	}
	*pi++
	switch r.Kind {
	case GoroutineRunning, GoroutineUser:
		return r, nil
	}
	if *pi+1 >= len(args) {
		return nil, fmt.Errorf("%s %s needs to be followed by an expression", args[*pi-1], args[*pi])
	}
	r.Arg = args[*pi+1]
	*pi++

	return r, nil
}

type ExamineMemoryArgs struct {
	Operand string
	Count   int64
	Size    int64
	IsExpr  bool
	Format  byte
	RawOut  bool
}

func ParseExamineMemoryArg(argstr string) (*ExamineMemoryArgs, error) {
	// default args

View on GitHub (pinned to a23773e6c3)

Solutions

1. Add the expression after the kind, e.g. 'goroutines -with function main.worker'.
2. Quote expressions containing spaces: 'goroutines -with label "my worker"'.
3. Use 'running' or 'user' if you did not intend to pass a value.

Example fix

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

func filterNeedsExpr(kind string) bool {
	return kind != "running" && kind != "user"
}
// if filterNeedsExpr(kind), ensure an expression token follows before calling the API

if _, err := api.ParseGoroutineArgs(args); err != nil {
	return fmt.Errorf("filter needs expression: %v", err)
}

When it happens

Trigger: Calling ParseGoroutineArgs with 'goroutines -with label' (kind parsed but no expression follows) - the kind itself was valid but its required expression is missing.

Common situations: A value containing spaces that the shell consumed; forgetting the label/regex after the kind; empty trailing token stripped by shell word-splitting.

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

• illegal commandline '%s'
• %s must be followed by an argument
• unrecognized argument to %s %s
• %q is not a valid format
• unknown option %q

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/0bf8d866f3b89b4f. Report an issue: GitHub.