Function isSubpath

packages/core/src/utils/paths.ts:211–223

(parentPath: string, childPath: string)

 * @returns True if childPath is a subpath of parentPath, false otherwise.
 */
export function isSubpath(parentPath: string, childPath: string): boolean {
  const isWindows = os.platform() === 'win32';
  const pathModule = isWindows ? path.win32 : path;

  // On Windows, path.relative is case-insensitive. On POSIX, it's case-sensitive.
  const relative = pathModule.relative(parentPath, childPath);

  return (
    !relative.startsWith(`..${pathModule.sep}`) &&
    relative !== '..' &&
    !pathModule.isAbsolute(relative)
  );
}