Function validateSymbol

src/math-json/symbols.ts:97–142

(
  s: unknown
)

  // Non-ASCII symbols
  return /^[\p{XIDS}_]\p{XIDC}*$/u.test(s);
}

const VS16 = '\\u{FE0F}'; // Variation Selector-16, forces emoji presentation
const KEYCAP = '\\u{20E3}'; // Combining Enclosing Keycap
const ZWJ = '\\u{200D}'; // Zero Width Joiner

const FLAG_SEQUENCE = '\\p{RI}\\p{RI}';

const TAG_MOD = `(?:[\\u{E0020}-\\u{E007E}]+\\u{E007F})`;
const EMOJI_MOD = `(?:\\p{EMod}|${VS16}${KEYCAP}?|${TAG_MOD})`;
// Exclude ASCII chars (#, *, 0-9) which have the Emoji property in Unicode
// but should not be treated as emoji symbols
const EMOJI_NOT_SYMBOL = `(?:(?=\\P{XIDC})(?=[^\\x23\\x2a\\x30-\\x39])\\p{Emoji})`;
const ZWJ_ELEMENT = `(?:${EMOJI_NOT_SYMBOL}${EMOJI_MOD}*|\\p{Emoji}${EMOJI_MOD}+|${FLAG_SEQUENCE})`;
const POSSIBLE_EMOJI = `(?:${ZWJ_ELEMENT})(${ZWJ}${ZWJ_ELEMENT})*`;
const SOME_EMOJI = new RegExp(`(?:${POSSIBLE_EMOJI})+`, 'u');
export const EMOJIS = new RegExp(`^(?:${POSSIBLE_EMOJI})+$`, 'u');

// Examine the string and return a string indicating if it's a valid symbol,
// and if not, why not.
// Useful for debugging. In production, use `isValidSymbol()` instead.
export function validateSymbol(
  s: unknown
):
  | 'valid'
  | 'not-a-string'
  | 'empty-string'
  | 'expected-nfc'
  | 'unexpected-mixed-emoji'
  | 'unexpected-bidi-marker'
  | 'unexpected-script'
  | 'invalid-first-char'
  | 'invalid-char' {
  if (typeof s !== 'string') return 'not-a-string';

  // console.log([...s].map((x) => x.codePointAt(0)!.toString(16)).join(' '));

  if (s === '') return 'empty-string';

  // MathJSON symbols are always stored in Unicode NFC canonical order.
  // See https://unicode.org/reports/tr15/
  if (s.normalize() !== s) return 'expected-nfc';

  // Does the string contain any bidi marker?
  // See https://www.unicode.org/L2/L2022/22028-bidi-prog.pdf
  // > For identifiers, there should be no need to allow
  // > [bidi control characters] at all, even if formally allowed.
  if (/[\u200E\u200F\u2066-\u2069\u202A-\u202E]/.test(s))
    return 'unexpected-bidi-marker';