Function deriveInstallDir

src/upgrade/index.ts:71–93

(
  bundleRoot: string,
  os: 'unix' | 'windows',
  exists: (p: string) => boolean
)

 *   windows: <installDir>\current             (bundleRoot)  → <installDir>
 */
export function deriveInstallDir(
  bundleRoot: string,
  os: 'unix' | 'windows',
  exists: (p: string) => boolean
): string | null {
  // Use the TARGET platform's path semantics (not the host's), so this is
  // deterministic when reasoning about a Windows layout from a POSIX host (CI)
  // and vice-versa. In production `os` always matches the running platform.
  const P = os === 'windows' ? path.win32 : path.posix;
  if (os === 'windows') {
    if (P.basename(bundleRoot).toLowerCase() === 'current') {
      return P.dirname(bundleRoot);
    }
    return null;
  }
  // unix: bundleRoot is <installDir>/versions/<version>
  const parent = P.dirname(bundleRoot);
  if (P.basename(parent) === 'versions') {
    const installDir = P.dirname(parent);
    return exists(installDir) ? installDir : P.dirname(parent);
  }
  return null;
}

export function detectInstallMethod(input: DetectInput): InstallMethod {
  const exists = input.exists ?? fs.existsSync;