This package provides show-indent-guides-mode which will render vertical bars at each level of indent. In addition to languages with a fixed indent offset such as C, it can be used in languages with arbitrary offsets such as Lisp. To avoid input lag, a longer idle delay is used in evil insert mode so that guides are not unnecessarily redrawn when characters are inserted on the end of a line. (Those not using Evil may wish to increase the value of shig-idle-time if they experience input lag.)
To render indent guides in code files:
(add-hook 'prog-mode-hook #'show-indent-guides-mode)