Issue #2572605 by Gábor Hojtsy, slasher13, Jo Fitzgerald, alexpott, andypost, Cottser, skyredwang, mfernea, joelpittet, jibran, larowlan, aleevas, Wim Leers, lauriii, catch, Berdir: Make Drupal 8 optionally working with Twig 2, while keeping its dependency on Twig 1