Prevent hooks from parent mode in derived mode

Question

I have:

(add-hook 'text-mode-hook 'turn-on-auto-fill)

but in lisp/nxml/nxml-mode.el:

(define-derived-mode nxml-mode text-mode "nXML"

All XML files is opened with auto-fill-mode. That is inconvenient because XML file under source control and shouldn't drastically change on edits.

How can I disable auto-fill for nxml? Should I remove:

(add-hook 'text-mode-hook 'turn-on-auto-fill)

or add some workaround for nxml?

Answer 1

Prevent hooks from parent mode in derived mode

Not trivial. I certainly can't think of a nice approach. You may find https://stackoverflow.com/a/19295380 of interest, though.

How can I disable auto-fill for nxml?

The trivial approach is to simply switch it off in nxml-mode-hook. The mode will be switched on, and almost immediately switched off again.

(add-hook 'nxml-mode-hook 'turn-off-auto-fill)

Alternatively, replace 'turn-on-auto-fill in your code with a custom function that does what you really want:

(defun my-turn-on-auto-fill-maybe ()
  "Turns on `auto-fill-mode' unless I don't want it."
  (let ((exceptions '(nxml-mode)))
    (unless (apply 'derived-mode-p exceptions)
      (auto-fill-mode 1))))