Function getFencedCodeRanges

actions/setup/js/sanitize_content_core.cjs:412–460

* Returns the character ranges [start, end) of fenced code blocks in markdown content. * Fenced code blocks are delimited by lines starting with 3+ backticks or 3+ tildes. * The returned ranges span from the first character of the opening fence line through * the last character of the closing fen

(s)

 * @returns {Array<[number, number]>} Array of [start, end) character positions
 */
function getFencedCodeRanges(s) {
  /** @type {Array<[number, number]>} */
  const ranges = [];
  const lines = s.split("\n");
  let pos = 0;
  let inBlock = false;
  let blockStart = -1;
  let fenceChar = "";
  let fenceLen = 0;

  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    const trimmed = line.trim();
    // Character position of the end of this line's content (not including the newline separator)
    const lineContentEnd = pos + line.length;
    // Character position after the newline separator (or same as lineContentEnd for the last line)
    const lineEnd = i < lines.length - 1 ? lineContentEnd + 1 : lineContentEnd;

    if (!inBlock) {
      const m = trimmed.match(/^(`{3,}|~{3,})/);
      if (m) {
        inBlock = true;
        blockStart = pos;
        fenceChar = m[1][0];
        fenceLen = m[1].length;
      }
    } else {
      // A closing fence: same character, at least as long, only whitespace after
      const fc = fenceChar === "`" ? "\\`" : "~";
      const closingRegex = new RegExp(`^[${fc}]{${fenceLen},}\\s*$`);
      if (closingRegex.test(trimmed)) {
        ranges.push([blockStart, lineEnd]);
        inBlock = false;
        blockStart = -1;
        fenceChar = "";
        fenceLen = 0;
      }
    }

    pos = lineEnd;
  }

  // Unclosed fence – treat the rest as code (safer fallback)
  if (inBlock && blockStart !== -1) {
    ranges.push([blockStart, s.length]);
  }

  return ranges;
}

/**
 * Applies a transformation function to a text segment while skipping inline code spans