toon-format/toon · error · SyntaxError

Invalid array length: "${seg}" (expected non-negative intege

Error message

Invalid array length: "${seg}" (expected non-negative integer with no leading zeros)

What it means

While parsing a TOON array header bracket segment like `[3]` or `[2,]`, the length part failed the BRACKET_LENGTH_PATTERN check (must be a non-negative integer with no leading zeros). This catches malformed headers such as `[03]`, `[-1]`, `[abc]`, or `[1.5]` so the decoder fails fast instead of mis-sizing the array.

Source

Thrown at packages/toon/src/decode/parser.ts:204

  if (content.endsWith(TAB)) {
    delimiter = DELIMITERS.tab
    content = content.slice(0, -1)
  }
  else if (content.endsWith(PIPE)) {
    delimiter = DELIMITERS.pipe
    content = content.slice(0, -1)
  }

  // Only a colon between the length and the optional delimiter symbol marks a keyed
  // header; any other placement leaves a token that fails the length check below.
  let keyed = false
  if (content.endsWith(COLON)) {
    keyed = true
    content = content.slice(0, -1)
  }

  if (!BRACKET_LENGTH_PATTERN.test(content)) {
    throw new SyntaxError(`Invalid array length: "${seg}" (expected non-negative integer with no leading zeros)`)
  }

  return { length: Number.parseInt(content, 10), delimiter, keyed }
}

/**
 * Parses the content of a field list into field entries, recursively
 * descending into nested field groups (`field{sub1,sub2}`).
 *
 * @remarks
 * Throws on empty segments, empty names, unmatched braces, and content
 * after a nested group's closing brace; callers decide strict fallthrough.
 */
export function parseFieldEntries(fieldsContent: string, delimiter: Delimiter): FieldNode[] {
  const entries = splitFieldEntries(fieldsContent, delimiter)

  return entries.map((entry) => {
    const trimmedEntry = trimSpaces(entry)

View on GitHub (pinned to 604eac266e)

Solutions

1. Fix the array header to use a plain non-negative integer with no leading zeros, e.g. `[3]` not `[03]`
2. Remove any negative signs, decimals, or extra characters inside the brackets
3. If the length is dynamic, format it with String(n) rather than padded formatting
4. Validate generated TOON output against the spec/test fixtures before persisting

Example fix

// before
items[03]{a,b}:
// after
items[3]{a,b}:

function hasValidArrayLengths(toonText) {
  return !/\[\s*(?:-|0\d|[^0-9\s])[0-9.,;\t]*\s*\]/.test(toonText)
}

try {
  const value = toon.decode(text)
} catch (err) {
  if (err instanceof SyntaxError && err.message.startsWith('Invalid array length')) {
    // surface header line / column to user for correction
  } else throw err
}

When it happens

Trigger: Calling toon.decode (which reaches parseBracketSegment via parseArrayHeaderLine) on input whose array header has an invalid length — leading zeros (`[03 items,]`), negative or non-integer lengths, or non-numeric content between the brackets.

Common situations: Hand-edited TOON files with adjusted array sizes written as `05`; generators that zero-pad lengths; copy-paste corruption turning `[4]` into `[-4]` or `[4x]`; writing array headers by hand without knowing the strict integer format.

Related errors

• result.reason
• Empty field name in field list
• Missing field name before nested field group
• Unmatched brace in field list
• Unexpected content after nested field group

AI-assisted analysis of toon-format/toon@604eac266e (2026-08-31). Data as JSON: /api/errors/c04e48991a5e67f4. Report an issue: GitHub.