Function nestedRepositoryBelow

src/sync/worktree.ts:147–167

(startPath: string, indexRoot: string)

 *     common dir): the #155 borrowed-worktree case, warned about, not refused.
 */
export function nestedRepositoryBelow(startPath: string, indexRoot: string): NestedRepository | null {
  // git needs an existing directory to run in: a file, or a sub-path that does
  // not exist yet, belongs to the repository of its nearest existing directory.
  let dir = path.resolve(startPath);
  while (!isDirectory(dir)) {
    const up = path.dirname(dir);
    if (up === dir) return null;
    dir = up;
  }
  const repoRoot = gitWorktreeRoot(dir);
  if (!repoRoot) return null;

  // The on-disk spelling of both ends (`realpathSync.native` normalizes case on
  // macOS and Windows), so `relPath` matches the paths the index stored.
  const rel = path.relative(nativeRealpath(indexRoot), nativeRealpath(repoRoot));
  if (!rel || rel === '..' || rel.startsWith(`..${path.sep}`) || path.isAbsolute(rel)) return null;

  const repoCommon = gitCommonDir(repoRoot);
  if (!repoCommon || repoCommon === gitCommonDir(realpath(indexRoot))) return null;
  return { root: repoRoot, relPath: rel.split(path.sep).join('/') };
}

function isDirectory(p: string): boolean {
  try {