Actually it must be named: "*Make `apply-on-rectangle' able to skip lines*".
Reattaching the patch as .txt


--- rect.el 2023-01-30 14:18:22.542176710 +0300
+++ rect-patched.el 2023-01-30 15:44:14.953579566 +0300
@@ -143,12 +143,16 @@
   (rectangle--reset-point-crutches))

 ;;; Rectangle operations.
+(defvar *rectangle-skip-lines* nil
+  "If `t' -- skip empty lines, if `function' -- skip line if it returns
`nil'.
+The function gets all arguments of `apply-to-rectangle' as input.")

 (defun apply-on-rectangle (function start end &rest args)
   "Call FUNCTION for each line of rectangle with corners at START, END.
 FUNCTION is called with two arguments: the start and end columns of the
 rectangle, plus ARGS extra arguments.  Point is at the beginning of line
when
 the function is called.
+Application of the FUNCTION is affected by the `*rectangle-skip-lines*'.
 The final point after the last operation will be returned."
   (save-excursion
     (let* ((cols (rectangle--pos-cols start end))
@@ -166,7 +170,14 @@
       (goto-char startpt)
       (while
           (progn
-            (apply function startcol endcol args)
+            (when (cond
+   ((null *rectangle-skip-lines*)
+ t)
+   ((functionp *rectangle-skip-lines*)
+ (apply *rectangle-skip-lines* function start end args))
+   (t
+ (/= (line-beginning-position) (line-end-position))))
+  (apply function startcol endcol args))
             (setq final-point (point))
             (and (zerop (forward-line 1)) (bolp)
                  (<= (point) endpt))))


On Mon, 30 Jan 2023 at 16:47, Constantin Kulikov <zxnotdead@gmail.com>
wrote:

>
>