this post was submitted on 18 Nov 2023
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Emacs: ediff basics (www.youtube.com)
submitted 11 months ago by geospeck@alien.top to c/emacs@communick.news
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[–] FitPandaFu@alien.top 1 points 11 months ago (3 children)

It can't even show white space differences

[–] invsblduck@alien.top 1 points 11 months ago (2 children)

Depends on the configured diff program and its options.

[–] geza42@alien.top 1 points 11 months ago (1 children)

This has nothing to do with the diff program. Ediff is not able to highlight whitespace differences like it highlights non-whitespace differences. Maybe it is possible to do somehow, but by default, whitespace differences generate a diff region with no highlights (or as ediff calls it, refinements).

It is because highlights are done on word level, and whitespaces are not words.

[–] invsblduck@alien.top 1 points 11 months ago

Oh, interesting.
I see.

Just popped open the Ediff code and there is a significant amount of effort put into ignoring whitespace. Like, it's not a shortcoming per se that it can't show this content but rather a deliberate onslaught to avoid it at all costs. The author must have been really annoyed by whitespace. 😂

I mostly use (ediff-buffers) in my day-to-day work in Spacemacs to compare two regions that I've narrowed to indirect buffers, and, interestingly, it does show me diffs that contain whitespace-only changes and prints the following to the echo area:

https://preview.redd.it/587vplu76e1c1.png?width=1896&format=png&auto=webp&s=e3d559ae695972f62865560b96f23953b4b26027

I did a quick test with other ediff functions bound in Spacemacs, and ediff-windows-linewise has the same behavior, but ediff-windows-wordwise does not -- it completely ignored diffs that were whitespace only and there was not even ## binding available in that ediff session.

When browsing the code, I found a local variable named ediff-whitespace (which u/doolio_ has already pointed out here in reply to you, actually), which is curious:

(defvar-local ediff-whitespace " \n\t\f\r\240"
  "Characters constituting white space.
These characters are ignored when differing regions are split into words.")

(\240 is Unicode symbol for nonbreakable whitespace.)

I wonder whether this variable can be set to nil.

PS:

It is because highlights are done on word level, and whitespaces are not words.

Apparently word splitting is configurable with ediff-forward-word-function ?