Change `standard-indent` for 1 specific major mode

Question

I author web apps with the web-mode in GNU Emacs, and I use 2 spaces for indentation.

After I examined the web-mode source, I found out that the mode defaults to the standard-indent variable, which in turn defaults to 4; and if standard-indent is unset, web-mode defaults to 2. I'm not sure if I got the terminology correct, and I guess some older versions of Emacs didn't set the variable, so I got 2-space indent out of the box.

Excerpt from web-mode.el:

(defcustom web-mode-css-indent-offset
  (if (and (boundp 'standard-indent) standard-indent) standard-indent 2)
  "CSS indentation level."
  :type 'integer
  :safe #'integerp
  :group 'web-mode)

Obviously, the custom variables' defaults are set during load.

How can I set standard-indent to 2 while web-mode loads? Given the way web-mode initializes its costomization variables, I think it has to be done while the mode is being loaded into Emacs, and not when I enter the major mode. How do I do that?

Answer 1

(add-hook 'web-mode-hook
          (lambda () (setq standard-indent 2)))

99% of all modes define at least one hook variable. Hook variables just hold a list of functions that will be called in the case of some event, usually upon entering some specific mode. Any time you want something to happen when a mode is activated, you want to add it to a hook function.

Edit: Yes, you're right. Just change the web-mode-css-indent-offset variable instead:

(add-hook 'web-mode-hook
          (lambda () (setq web-mode-css-indent-offset 2)))

Incidentally, since the web-mode-css-indent-offset has a name starting with web-mode, you can be fairly certain that no other mode is going to care what value it has. So you could just customize it. Type M-x customize-variable web-mode-css-indent-offset and it'll give you a UI that tells you all the help information about the variable, as well as letting you edit the and save the value for the variable.