d2lang/d2 · error

invalid kern table: no subtables

Error message

invalid kern table: no subtables

What it means

After the kern table header, nSubtables (bytes 2–4) must be non-zero; a version-0 kern table with zero subtables contains no kerning data at all, which the parser treats as malformed rather than empty.

Source

Thrown at lib/textmeasure/fontface.go:165

	} else {
		x -= int64(unitsPerEm) / 2
	}
	return fixed.Int26_6(x / int64(unitsPerEm))
}

func parseLegacyKern(src []byte) ([]kernPair, error) {
	table, err := sfntTable(src, "kern")
	if err != nil || table == nil {
		return nil, err
	}
	if len(table) < 18 {
		return nil, fmt.Errorf("invalid kern table: too short")
	}
	if binary.BigEndian.Uint16(table[0:2]) != 0 {
		return nil, fmt.Errorf("unsupported kern table version")
	}
	if binary.BigEndian.Uint16(table[2:4]) == 0 {
		return nil, fmt.Errorf("invalid kern table: no subtables")
	}

	length := int(binary.BigEndian.Uint16(table[6:8]))
	coverage := binary.BigEndian.Uint16(table[8:10])
	if coverage != 0x0001 {
		return nil, fmt.Errorf("unsupported kern table coverage 0x%04x", coverage)
	}
	n := int(binary.BigEndian.Uint16(table[10:12]))
	if length < 14 || 6*n != length-14 || 4+length > len(table) {
		return nil, fmt.Errorf("invalid kern table length")
	}

	pairs := make([]kernPair, n)
	for i := range pairs {
		offset := 18 + 6*i
		pairs[i] = kernPair{
			key:   binary.BigEndian.Uint32(table[offset : offset+4]),
			value: int16(binary.BigEndian.Uint16(table[offset+4 : offset+6])),

View on GitHub (pinned to 0d69dca6f5)

Solutions

1. Remove the empty kern table entirely with fonttools so the parser skips it gracefully.
2. Regenerate/re-download the font from the original source.
3. Verify with fonttools (f['kern'].kernTables) that the table actually contains subtables; if kerning lives in GPOS, accept reduced kerning fidelity or pre-convert the font.

Example fix

# python fonttools: drop the empty kern table
from fontTools.ttLib import TTFont
f = TTFont('broken.ttf')
if 'kern' in f and not f['kern'].kernTables:
    del f['kern']
f.save('fixed.ttf')

// nSubtables := binary.BigEndian.Uint16(kern[2:4]); usable := nSubtables != 0

pairs, err := parseLegacyKern(fontData)
if err != nil {
    log.Printf("kerning unavailable (%v), continuing without", err)
    pairs = nil
}

When it happens

Trigger: parseFont loads a font whose kern table declares version 0 but nSubtables == 0, typically from a broken subsetting or editing operation.

Common situations: Fonts processed by buggy subsetting tools; fonts where GPOS kerning was added and the legacy kern table emptied but not removed.

Related errors

• invalid kern table: too short
• unsupported kern table version
• unsupported kern table coverage 0x%04x
• invalid kern table length
• checksum error in table: %v

AI-assisted analysis of d2lang/d2@0d69dca6f5 (2026-08-31). Data as JSON: /api/errors/1d633d533a44a44e. Report an issue: GitHub.