Function canonicalFuturePath

packages/migrate/src/node.ts:213–233

* Resolves every existing prefix through realpath and appends only missing * path segments. This detects an existing symlink that redirects a future * output outside its declared root without creating any directory first.

(path: string)

 * output outside its declared root without creating any directory first.
 */
async function canonicalFuturePath(path: string): Promise<string> {
  const missing: string[] = [];
  let existing = path;
  let canonicalExisting: string | undefined;
  while (canonicalExisting === undefined) {
    try {
      canonicalExisting = await realpath(existing);
    } catch (error: unknown) {
      if (!isMissingPathError(error)) throw error;
      const parent = dirname(existing);
      if (parent === existing) throw error;
      missing.push(basename(existing));
      existing = parent;
    }
  }
  if (missing.length > 0) {
    const existingStats = await stat(canonicalExisting);
    if (!existingStats.isDirectory()) throw new Error(`An output path ancestor is not a directory: ${existing}`);
  }
  return resolve(canonicalExisting, ...missing.reverse());
}

function isMissingPathError(error: unknown): error is NodeJS.ErrnoException {
  return error instanceof Error && 'code' in error && error.code === 'ENOENT';