How to never have a major mode enabled automatically

Question

looks like Emacs tries to be smart, switching to an annoying change-log-mode often when i am editing a changelog file. I would like to disable it, but i just find info about how to interactively disable a mode while editing a buffer, or how to enable a mode when a file matches a pattern.

I cannot find any info about how to disable a major mode totally and in any case. Ideally i would even remove it from my installation, as i will be never using it

Answer 1

Emacs keeps a list of regexp-mode pairs in an alist called auto-mode-alist. Any file you open has it's name matched against the nodes in the alist; every match activates a mode.

So, what you want to do, it sounds like, is purge change-log-mode from auto-mode-alist, which you can do in your init.el/.emacs.d/etc like so:

(rassq-delete-all 'change-log-mode auto-mode-alist)

Answer 2

Here are two sledgehammer approaches:

(defun change-log-mode () t)

which redefines change-log-mode to do nothing, and

(fset 'change-log-mode (symbol-function 'fundamental-mode))

which makes change-log-mode turn on fundamental mode instead.

A third approach might be to use an overriding advice.

And a somewhat less drastic approach is to remove all mention of the offending mode from auto-mode-alist:

(require 'cl)
(setq auto-mode-alist
      (remove-if (lambda (pair) (eq (cdr pair) 'change-log-mode))
                 auto-mode-alist))

This way, you are not disabling the mode altogether, but it should never be automatically applied (unless some other mechanism turns it on).

Answer 3

You need to modify the auto-mode-alist variable. This is “alist of filename patterns vs corresponding major mode functions”. Its value looks like this (at least for me):

(
 …
 ("[cC]hange\\.?[lL]og?\\'" . change-log-mode)
 ("[cC]hange[lL]og[-.][0-9]+\\'" . change-log-mode)
 ("\\$CHANGE_LOG\\$\\.TXT" . change-log-mode)
 …
 ("[cC]hange[lL]og[-.][-0-9a-z]+\\'" . change-log-mode)
 …
)

So, you just need to either push something that matches these regexps on top of the list or remove these items. I think pushing is a better idea because you don't need to traverse all contents of the list, so here we go:

(push '("[cC]hange\\.?[lL]og?\\'" . text-mode) auto-mode-alist)

Here I “disabled” the first regexp, so plain text-mode will be used for files that match it from now on (this method has the additional benefit that you can specify which mode to use instead because fundamental-mode may be not very interesting). You can do the same to the other regexps.