master e0f3a4d4b2a 1/2: Fix :align-to when line numbers are displayed

branch: master
commit e0f3a4d4b2a47bcf56acd99ddadb9c21a5811a80
Author: Aaron Jensen <[email protected]>
Commit: Eli Zaretskii <[email protected]>

    Fix :align-to when line numbers are displayed
    
    * src/xdisp.c (calc_pixel_width_or_height): Don't account for the
    line-number display more than once.  (Bug#81253)
    
    * test/lisp/visual-wrap-tests.el
    (visual-wrap-tests/line-numbers-align-to-wrap-prefix): New test.
---
 src/xdisp.c                    | 23 ++++++++++++++++++-----
 test/lisp/visual-wrap-tests.el | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/src/xdisp.c b/src/xdisp.c
index e2321762699..6e910978bd7 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -30452,7 +30452,7 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       /* ':align_to'.  First time we compute the value, window
 	 elements are interpreted as the position of the element's
 	 left edge.  */
-      if (align_to && *align_to < 0)
+      if (align_to && *align_to == -1)
 	{
 	  *res = 0;
 	  /* 'left': left edge of the text area.  */
@@ -30517,8 +30517,14 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       int base_unit = (width_p
 		       ? FRAME_COLUMN_WIDTH (it->f)
 		       : FRAME_LINE_HEIGHT (it->f));
-      if (width_p && align_to && *align_to < 0)
-	return OK_PIXELS (XFLOATINT (prop) * base_unit + lnum_pixel_width);
+      /* `align_to' starts at -1.  A numeric value without an explicit
+	 base is relative to the text area's left edge, so account for
+	 line numbers once and mark the default base as consumed.  */
+      if (width_p && align_to && *align_to == -1)
+	{
+	  *align_to = -2;
+	  return OK_PIXELS (XFLOATINT (prop) * base_unit + lnum_pixel_width);
+	}
       return OK_PIXELS (XFLOATINT (prop) * base_unit);
     }
 
@@ -30579,8 +30585,15 @@ calc_pixel_width_or_height (double *res, struct it *it, Lisp_Object prop,
       if (NUMBERP (car))
 	{
 	  double fact;
-	  int offset =
-	    width_p && align_to && *align_to < 0 ? lnum_pixel_width : 0;
+	  int offset = 0;
+	  /* See the NUMBERP case above: the default text-area base
+	     should apply once to the whole pixel expression, not once
+	     for each numeric subexpression.  */
+	  if (width_p && align_to && *align_to == -1)
+	    {
+	      offset = lnum_pixel_width;
+	      *align_to = -2;
+	    }
 	  pixels = XFLOATINT (car);
 	  if (NILP (cdr))
 	    return OK_PIXELS (pixels + offset);
diff --git a/test/lisp/visual-wrap-tests.el b/test/lisp/visual-wrap-tests.el
index a1f286cf96a..6817e82bc8b 100644
--- a/test/lisp/visual-wrap-tests.el
+++ b/test/lisp/visual-wrap-tests.el
@@ -178,4 +178,37 @@ property is installed on line 1.  See bug#81039."
                       (ensure-list
                        (get-text-property (point-min) 'display))))))
 
+(ert-deftest visual-wrap-tests/line-numbers-align-to-wrap-prefix ()
+  "With line numbers, `wrap-prefix' `:align-to' aligns from text start."
+  (skip-unless (display-graphic-p))
+  (let ((buffer (generate-new-buffer " *visual-wrap-test*")))
+    (unwind-protect
+        (let ((window (display-buffer buffer)))
+          (with-selected-window window
+            (setq-local display-line-numbers t)
+            (visual-line-mode 1)
+            (let* ((columns (window-width))
+                   ;; Make the first word fit on visual line 1, but leave
+                   ;; too little room for the second word so word wrapping
+                   ;; moves it to visual line 2.
+                   (first-word-width (max 10 (- columns 20))))
+              (insert "- "
+                      (make-string first-word-width ?n)
+                      " "
+                      (make-string 20 ?n)))
+            (visual-wrap-prefix-function (point-min) (point-max))
+            (redisplay t)
+            (let* ((bol-x (car (posn-x-y (posn-at-point (point-min)))))
+                   (prefix-width (string-pixel-width "- " (current-buffer)))
+                   (second-word-pos
+                    (save-excursion
+                      (goto-char (point-min))
+                      (search-forward " " nil t 2)
+                      (point)))
+                   (second-word-x
+                    (car (posn-x-y (posn-at-point second-word-pos)))))
+              (should (= second-word-x (+ bol-x prefix-width))))))
+      (when (buffer-live-p buffer)
+        (kill-buffer buffer)))))
+
 ;; visual-wrap-tests.el ends here