index.ts

import * as charCodes from "charcodes";

// The following character codes are forbidden from being
// an immediate sibling of NumericLiteralSeparator _
const forbiddenNumericSeparatorSiblings = {
  decBinOct: new Set<number>([
    charCodes.dot,
    charCodes.uppercaseB,
    charCodes.uppercaseE,
    charCodes.uppercaseO,
    charCodes.underscore, // multiple separators are not allowed
    charCodes.lowercaseB,
    charCodes.lowercaseE,
    charCodes.lowercaseO,
  ]),
  hex: new Set<number>([
    charCodes.dot,
    charCodes.uppercaseX,
    charCodes.underscore, // multiple separators are not allowed
    charCodes.lowercaseX,
  ]),
};

const isAllowedNumericSeparatorSibling = {
  // 0 - 1
  bin: (ch: number) => ch === charCodes.digit0 || ch === charCodes.digit1,

  // 0 - 7
  oct: (ch: number) => ch >= charCodes.digit0 && ch <= charCodes.digit7,

  // 0 - 9
  dec: (ch: number) => ch >= charCodes.digit0 && ch <= charCodes.digit9,

  // 0 - 9, A - F, a - f,
  hex: (ch: number) =>
    (ch >= charCodes.digit0 && ch <= charCodes.digit9) ||
    (ch >= charCodes.uppercaseA && ch <= charCodes.uppercaseF) ||
    (ch >= charCodes.lowercaseA && ch <= charCodes.lowercaseF),
};

export type StringContentsErrorHandlers = EscapedCharErrorHandlers & {
  unterminated(
    initialPos: number,
    initialLineStart: number,
    initialCurLine: number,
  ): void;
};

export function readStringContents(
  type: "single" | "double" | "template",
  input: string,
  pos: number,
  lineStart: number,
  curLine: number,
  errors: StringContentsErrorHandlers,
) {
  const initialPos = pos;
  const initialLineStart = lineStart;
  const initialCurLine = curLine;

  let out = "";
  let containsInvalid = false;
  let chunkStart = pos;
  const { length } = input;
  for (;;) {
    if (pos >= length) {
      errors.unterminated(initialPos, initialLineStart, initialCurLine);
      out += input.slice(chunkStart, pos);
      break;
    }
    const ch = input.charCodeAt(pos);
    if (isStringEnd(type, ch, input, pos)) {
      out += input.slice(chunkStart, pos);
      break;
    }
    if (ch === charCodes.backslash) {
      out += input.slice(chunkStart, pos);
      let escaped;
      ({
        ch: escaped,
        pos,
        lineStart,
        curLine,
      } = readEscapedChar(
        input,
        pos,
        lineStart,
        curLine,
        type === "template",
        errors,
      ));
      if (escaped === null) {
        containsInvalid = true;
      } else {
        out += escaped;
      }
      chunkStart = pos;
    } else if (
      ch === charCodes.lineSeparator ||
      ch === charCodes.paragraphSeparator
    ) {
      ++pos;
      ++curLine;
      lineStart = pos;
    } else if (ch === charCodes.lineFeed || ch === charCodes.carriageReturn) {
      if (type === "template") {
        out += input.slice(chunkStart, pos) + "\n";
        ++pos;
        if (
          ch === charCodes.carriageReturn &&
          input.charCodeAt(pos) === charCodes.lineFeed
        ) {
          ++pos;
        }
        ++curLine;
        chunkStart = lineStart = pos;
      } else {
        errors.unterminated(initialPos, initialLineStart, initialCurLine);
      }
    } else {
      ++pos;
    }
  }
  return { pos, str: out, containsInvalid, lineStart, curLine };
}

function isStringEnd(
  type: "single" | "double" | "template",
  ch: number,
  input: string,
  pos: number,
) {
  if (type === "template") {
    return (
      ch === charCodes.graveAccent ||
      (ch === charCodes.dollarSign &&
        input.charCodeAt(pos + 1) === charCodes.leftCurlyBrace)
    );
  }
  return (
    ch === (type === "double" ? charCodes.quotationMark : charCodes.apostrophe)
  );
}

export type EscapedCharErrorHandlers = HexCharErrorHandlers &
  CodePointErrorHandlers & {
    strictNumericEscape(pos: number): void;
  };

export function readEscapedChar(
  input: string,
  pos: number,
  lineStart: number,
  curLine: number,
  inTemplate: boolean,
  errors: EscapedCharErrorHandlers,
) {
  const throwOnInvalid = !inTemplate;
  pos++; // skip '\'

  const res = (ch: string | null) => ({ pos, ch, lineStart, curLine });

  const ch = input.charCodeAt(pos++);
  switch (ch) {
    case charCodes.lowercaseN:
      return res("\n");
    case charCodes.lowercaseR:
      return res("\r");
    case charCodes.lowercaseX: {
      let code;
      ({ code, pos } = readHexChar(
        input,
        pos,
        2,
        false,
        throwOnInvalid,
        errors,
      ));
      return res(code === null ? null : String.fromCharCode(code));
    }
    case charCodes.lowercaseU: {
      let code;
      ({ code, pos } = readCodePoint(input, pos, throwOnInvalid, errors));
      return res(code === null ? null : String.fromCodePoint(code));
    }
    case charCodes.lowercaseT:
      return res("\t");
    case charCodes.lowercaseB:
      return res("\b");
    case charCodes.lowercaseV:
      return res("\u000b");
    case charCodes.lowercaseF:
      return res("\f");
    case charCodes.carriageReturn:
      if (input.charCodeAt(pos) === charCodes.lineFeed) {
        ++pos;
      }
    // fall through
    case charCodes.lineFeed:
      lineStart = pos;
      ++curLine;
    // fall through
    case charCodes.lineSeparator:
    case charCodes.paragraphSeparator:
      return res("");
    case charCodes.digit8:
    case charCodes.digit9:
      if (inTemplate) {
        return res(null);
      } else {
        errors.strictNumericEscape(pos - 1);
      }
    // fall through
    default:
      if (ch >= charCodes.digit0 && ch <= charCodes.digit7) {
        const startPos = pos - 1;
        const match = input.slice(startPos, pos + 2).match(/^[0-7]+/)!;

        let octalStr = match[0];

        let octal = parseInt(octalStr, 8);
        if (octal > 255) {
          octalStr = octalStr.slice(0, -1);
          octal = parseInt(octalStr, 8);
        }
        pos += octalStr.length - 1;
        const next = input.charCodeAt(pos);
        if (
          octalStr !== "0" ||
          next === charCodes.digit8 ||
          next === charCodes.digit9
        ) {
          if (inTemplate) {
            return res(null);
          } else {
            errors.strictNumericEscape(startPos);
          }
        }

        return res(String.fromCharCode(octal));
      }

      return res(String.fromCharCode(ch));
  }
}

type HexCharErrorHandlers = IntErrorHandlers & {
  invalidEscapeSequence(pos: number, startPos: number): void;
};

// Used to read character escape sequences ('\x', '\u').
function readHexChar(
  input: string,
  pos: number,
  len: number,
  forceLen: boolean,
  throwOnInvalid: boolean,
  errors: HexCharErrorHandlers,
) {
  const initialPos = pos;
  let n;
  ({ n, pos } = readInt(input, pos, 16, len, forceLen, false, errors));
  if (n === null) {
    if (throwOnInvalid) {
      errors.invalidEscapeSequence(pos, initialPos);
    } else {
      pos = initialPos - 1;
    }
  }
  return { code: n, pos };
}

export type IntErrorHandlers = {
  numericSeparatorInEscapeSequence(pos: number): void;
  unexpectedNumericSeparator(pos: number): void;
  // It can return "true" to indicate that the error was handled
  // and the int parsing should continue.
  invalidDigit(pos: number, radix: number): boolean;
};

export function readInt(
  input: string,
  pos: number,
  radix: number,
  len: number | undefined,
  forceLen: boolean,
  allowNumSeparator: boolean | "bail",
  errors: IntErrorHandlers,
) {
  const start = pos;
  const forbiddenSiblings =
    radix === 16
      ? forbiddenNumericSeparatorSiblings.hex
      : forbiddenNumericSeparatorSiblings.decBinOct;
  const isAllowedSibling =
    radix === 16
      ? isAllowedNumericSeparatorSibling.hex
      : radix === 10
      ? isAllowedNumericSeparatorSibling.dec
      : radix === 8
      ? isAllowedNumericSeparatorSibling.oct
      : isAllowedNumericSeparatorSibling.bin;

  let invalid = false;
  let total = 0;

  for (let i = 0, e = len == null ? Infinity : len; i < e; ++i) {
    const code = input.charCodeAt(pos);
    let val;

    if (code === charCodes.underscore && allowNumSeparator !== "bail") {
      const prev = input.charCodeAt(pos - 1);
      const next = input.charCodeAt(pos + 1);

      if (!allowNumSeparator) {
        errors.numericSeparatorInEscapeSequence(pos);
      } else if (
        Number.isNaN(next) ||
        !isAllowedSibling(next) ||
        forbiddenSiblings.has(prev) ||
        forbiddenSiblings.has(next)
      ) {
        errors.unexpectedNumericSeparator(pos);
      }

      // Ignore this _ character
      ++pos;
      continue;
    }

    if (code >= charCodes.lowercaseA) {
      val = code - charCodes.lowercaseA + charCodes.lineFeed;
    } else if (code >= charCodes.uppercaseA) {
      val = code - charCodes.uppercaseA + charCodes.lineFeed;
    } else if (charCodes.isDigit(code)) {
      val = code - charCodes.digit0; // 0-9
    } else {
      val = Infinity;
    }
    if (val >= radix) {
      // If we found a digit which is too big, errors.invalidDigit can return true to avoid
      // breaking the loop (this is used for error recovery).
      if (val <= 9 && errors.invalidDigit(pos, radix)) {
        val = 0;
      } else if (forceLen) {
        val = 0;
        invalid = true;
      } else {
        break;
      }
    }
    ++pos;
    total = total * radix + val;
  }
  if (pos === start || (len != null && pos - start !== len) || invalid) {
    return { n: null, pos };
  }

  return { n: total, pos };
}

export type CodePointErrorHandlers = HexCharErrorHandlers & {
  invalidCodePoint(pos: number): void;
};

export function readCodePoint(
  input: string,
  pos: number,
  throwOnInvalid: boolean,
  errors: CodePointErrorHandlers,
) {
  const ch = input.charCodeAt(pos);
  let code;

  if (ch === charCodes.leftCurlyBrace) {
    ++pos;
    ({ code, pos } = readHexChar(
      input,
      pos,
      input.indexOf("}", pos) - pos,
      true,
      throwOnInvalid,
      errors,
    ));
    ++pos;
    if (code !== null && code > 0x10ffff) {
      if (throwOnInvalid) {
        errors.invalidCodePoint(pos);
      } else {
        return { code: null, pos };
      }
    }
  } else {
    ({ code, pos } = readHexChar(input, pos, 4, false, throwOnInvalid, errors));
  }
  return { code, pos };
}