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I'd like to highlight only the text in between the leading and trailing whitespace on each line. For example, I'd only like to highlight the region marked by the double arrow <--> for the following line:

    public static void printSum() {...}
    <--------------------------------->

I run Doom Emacs and understand that hl-line-mode is responsible for highlighting the current line. It appears that if I defined my own hl-line-range-function to do what I wanted, I could apply this to any major mode (I want it on the dashboard).

It seems that hl-line-range-function needs to return a cons cell of the starting and ending "positions" of where I'd like to highlight. What is the "position" data type? How is it represented? Can I simply return the value of functions like end-of-visual-line and back-to-indentation?

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  • emacs.stackexchange.com/tags/elisp/info
    – Drew
    Commented Dec 27, 2022 at 0:15
  • A guess, without looking, is that "position" is just a buffer position. If so, the after moving with either of those functions you need to return (point). And you can wrap the movement and call to point in a save-excursion. On the other hand, maybe there's a function that gives you the position directly. At least the doc of those functions doesn't claim that they do, so even if they might you shouldn't count on that.
    – Drew
    Commented Dec 27, 2022 at 0:19
  • It would be easier to do this by setting the :extend attribute of the hl-line face to nil. When it's set to nil, the hl-line highlight will only affect positions of the line where characters are located (including whitespace). If you want it to only be effective in the dashboard, you can create a new face and use setq-local in dashboard-mode's hook to set that face as the value of hl-line-face only in the dashboard buffer.
    – mmarshall540
    Commented Feb 1, 2023 at 6:22

1 Answer 1

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As Drew suggested, this works:

(defun my-hl-line-range-function ()
  (let ((beg (save-excursion
           (back-to-indentation)
           (point)))
        (end (save-excursion
           (end-of-visual-line)
           (point))))
    (cons beg end)))

(setq hl-line-range-function #'my-hl-line-range-function)
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