Function loopBody

packages/hosts/mcp/src/create-artifact.ts:131–174

(code: string, keyword: string, afterKeyword: number)

 *  can't be delimited confidently (unbalanced braces, generator-mangled source)
 *  — in which case nothing is reported rather than something guessed. */
const loopBody = (code: string, keyword: string, afterKeyword: number): string | null => {
  let index = afterKeyword;
  const skipSpace = (): void => {
    while (index < code.length && /\s/.test(code[index] ?? "")) index += 1;
  };

  // `for (...)` / `while (...)`: step over the header's parens first. A hook in
  // the header itself is not the shape we're after.
  if (keyword !== "do") {
    skipSpace();
    if (code[index] !== "(") return null;
    let depth = 0;
    for (; index < code.length; index += 1) {
      if (code[index] === "(") depth += 1;
      else if (code[index] === ")") {
        depth -= 1;
        if (depth === 0) {
          index += 1;
          break;
        }
      }
    }
    if (depth !== 0) return null;
  }

  skipSpace();

  // Only a braced body is scanned. A braceless one has no delimiter to trust —
  // its end would have to be guessed at the next semicolon, which in JSX prose
  // can run far past the statement and reach an unrelated hook. Giving up costs
  // only `for (…) useQuery(…)`, which no generator writes.
  if (code[index] !== "{") return null;

  const start = index;
  let depth = 0;
  for (; index < code.length; index += 1) {
    if (code[index] === "{") depth += 1;
    else if (code[index] === "}") {
      depth -= 1;
      if (depth === 0) return code.slice(start + 1, index);
    }
  }
  return null;
};

/** `do` is also an ordinary English word that can appear in JSX text ahead of an
 *  expression container ("nothing to do {count}"), where `for`/`while` are