Proper way to provide a default optional parameter

Question

I like doing PR reviews with Magit's diff, thus calling magit-diff-visit-file pretty often, providing a universal argument for the optional other-window parameter. To optimize the process instead of pressing C-- <Ret> i'd prefer just to use <Ret> key. What's the proper way to define such a behaviour?

I've seen people using defalias here and there, but not sure how's it going to work in terms of itself. I guess i can get away with defining a stub function and forward the call to magit-diff-visit-file, but i was thinking if there's a better way?

Answer 1

defalias is useful when you want to give some existing function an alternative name. But you want to change what a certain key does, and that's a different problem.

You have to bind "RET" to some command in some keymap, a problem that can be broken down into two smaller problems: "what keymap?" and "what command?".

To find the appropriate keymap you can use rgrep in the directory containing the Magit source to search for magit-diff-visit-file.

Turns out you actually have to modify two keymaps magit-file-section-map and magit-hunk-section-map and that instead of "RET" you should use [remap magit-visit-thing], though the former would work too.

(define-key magit-file-section-map [remap magit-visit-thing] '???)
(define-key magit-hunk-section-map [remap magit-visit-thing] '???)

Looking at the other matches and the code in close approximation suggests that no variation exists that behaves the way you want, but defining it is easy: copy magit-diff-visit-file, replace the body with a call to that function and adjust the name, signature and interactive form.

(defun magit-diff-visit-file-other-window (file)
  (interactive (list (--if-let (magit-file-at-point)
                         (expand-file-name it)
                       (user-error "No file at point"))))
  (magit-diff-visit-file file t))