What causes "invalid row range [%v, %v], line count : %v" in yorukot/superfile?

Clamp endRow to len(lines)-1 and stRow to >= 0 before calling validateComponentPlacement

invalid row range [%v, %v], line count : %v

Error message

invalid row range [%v, %v], line count : %v

What it means

extractComponent slices a rectangular region out of rendered lines and first validates the row bounds. This error is thrown when pos.stRow is negative, stRow > endRow, or endRow is beyond the last line (len(lines)). The message includes the requested range and the actual line count for debugging.

Source

Thrown at src/internal/validation.go:401

func (m *model) validateComponentPlacement(lines []string, pos compPosition, border bool) error {
	extractedLines, err := m.extractComponent(lines, pos)
	if err != nil {
		return fmt.Errorf("failure while extracting content : %w", err)
	}

	cntRow := pos.endRow - pos.stRow + 1
	cntCol := pos.endCol - pos.stCol + 1
	extractedOut := strings.Join(extractedLines, "\n")
	if err := validateRender(extractedOut, cntRow, cntCol, border); err != nil {
		return fmt.Errorf("failure in extracted content : %w", err)
	}
	return nil
}

// Inclusive
func (m *model) extractComponent(lines []string, pos compPosition) ([]string, error) {
	if 0 > pos.stRow || pos.stRow > pos.endRow || pos.endRow >= len(lines) {
		return nil, fmt.Errorf("invalid row range [%v, %v], line count : %v",
			pos.stRow, pos.endRow, len(lines))
	}
	firstLineWidth := ansi.StringWidth(lines[0])
	if 0 > pos.stCol || pos.stCol > pos.endCol || pos.endCol >= firstLineWidth {
		return nil, fmt.Errorf("invalid col range [%v, %v], first line width : %v",
			pos.stCol, pos.endCol, firstLineWidth)
	}

	cntRow := pos.endRow - pos.stRow + 1
	extractedLines := make([]string, cntRow)
	for i := range cntRow {
		orgIdx := pos.stRow + i
		extractedLines[i] = ansi.Cut(lines[orgIdx], pos.stCol, pos.endCol+1)
	}
	return extractedLines, nil
}

type compPosition struct {

View on GitHub (pinned to b72f550bc6)

Solutions

Clamp endRow to len(lines)-1 and stRow to >= 0 before calling validateComponentPlacement
Check terminal size handling: ensure the layout doesn't allocate more rows than available
Log len(lines) vs requested rows to find the off-by-one
Recompute compPosition from the freshly rendered content instead of cached values

Example fix

// before
m.validateComponentPlacement(lines, pos, border)
// after
if pos.endRow >= len(lines) {
	pos.endRow = len(lines) - 1
}
if pos.stRow < 0 {
	pos.stRow = 0
}
if pos.stRow <= pos.endRow {
	m.validateComponentPlacement(lines, pos, border)
}

Defensive patterns

Strategy: validation

Validate before calling

func rowsInRange(lines []string, pos compPosition) bool {
	return pos.stRow >= 0 && pos.stRow <= pos.endRow && pos.endRow < len(lines)
}

Try / catch

if err := m.validateComponentPlacement(lines, pos, border); err != nil {
	var rngErr = err // message contains range and line count
	log.Printf("row bounds violated: %v", rngErr)
	return fmt.Errorf("skipping validation for %v: %w", pos, err)
}

Prevention

Always clamp endRow to len(lines)-1 before extraction
Handle empty render output (len(lines)==0) explicitly
Verify terminal size is known before layout math
Prefer computing rows from the rendered slice length, not the desired height

When it happens

Trigger: Calling validateComponentPlacement (which calls extractComponent) with a compPosition whose rows exceed the rendered content — e.g., endRow >= len(lines) after a component shrank, or a negative stRow from a bad layout computation.

Common situations: Terminal too small so the rendered content has fewer lines than the component's allocated rows; stale position data after re-render; arithmetic error in layout math producing negative start row.

Related errors

AI-assisted analysis of yorukot/superfile@b72f550bc6 (2026-09-01). Data as JSON: /api/errors/1cf5f6dc6928b285. Report an issue: GitHub.