What causes "Invalid next count" in go-delve/delve?

Use a positive count, e.g. 'next 5'

Invalid next count

Error message

Invalid next count

What it means

The 'next' command accepts an optional repeat count so 'next 5' performs five next operations. This error is returned when the parsed count is zero or negative, since stepping a non-positive number of times is meaningless. parseOptionalCount accepts an empty argument (defaulting to 1) but any explicit value must be >= 1.

Source

Thrown at pkg/terminal/command.go:1545

func (c *Commands) next(t *Term, ctx callContext, args string) error {
	if err := scopePrefixSwitch(t, ctx); err != nil {
		return err
	}
	if c.frame != 0 {
		return errNotOnFrameZero
	}

	nextfn := t.client.Next
	if ctx.Prefix == revPrefix {
		nextfn = t.client.ReverseNext
	}

	var count int64
	var err error
	if count, err = parseOptionalCount(args); err != nil {
		return err
	} else if count <= 0 {
		return errors.New("Invalid next count")
	}
	for ; count > 0; count-- {
		state, err := exitedToError(nextfn())
		if err != nil {
			printcontextNoState(t)
			return err
		}
		// If we're about the exit the loop, print the context.
		finishedNext := count == 1
		if finishedNext {
			printcontext(t, state)
		}
		if err := continueUntilCompleteNext(t, state, "next", finishedNext); err != nil {
			return err
		}
	}
	return nil
}

View on GitHub (pinned to a23773e6c3)

Solutions

Use a positive count, e.g. 'next 5'
Omit the argument entirely for a single step ('next')
Use 'rev next N' for reverse stepping instead of a negative count

Example fix

// before
next 0
// after
next

Defensive patterns

Strategy: validation

Validate before calling

n, err := strconv.ParseInt(arg, 10, 64)
if arg != "" && (err != nil || n <= 0) {
	return errors.New("next count must be a positive integer")
}

Try / catch

if err := next(...); err != nil && strings.Contains(err.Error(), "Invalid next count") { /* clamp count to >= 1 and retry */ }

Prevention

Never pass 0 or negative counts to next
Use 'rev next' for reverse stepping, not negative counts
Guard scripted loop counters that compute the repeat count

When it happens

Trigger: Running 'next 0' or 'next -3': parseOptionalCount succeeds but the `count <= 0` check returns 'Invalid next count' (pkg/terminal/command.go:1545).

Common situations: Scripted stepping loops that compute a zero count; users confusing 0-based vs 1-based counts; typos like 'next -1' intending 'reverse next' (which is 'rev next').

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/04f08a1b252bd760. Report an issue: GitHub.