bug#68215: Bug in what-page

[Lars Brinkhoff <lars.brinkhoff@gmail.com>]

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Hello,

The Emacs manual says:
  "M-x what-page
   Display the page number of point, and the line number within that page."

I would argue that this is the intended function, since that is what
GNU Emacs did before 2010, and it is the same as "What Page" in the
original TECO Emacs.

Bug https://debbugs.gnu.org/cgi/bugreport.cgi?bug=6825 noted that the
line number was wrong if the cursor was not at the beginning of a
line.  There was a fix for this, but the fix only works for the first
page.  In subsequent pages, the line number is no longer relative to
the current page.

I'm attaching a patch which restores the original function and also
fixes the bug.  The updated test checks this.  I also updated the
what-page doc string to more clearly explain what line numbers are
reported.

[-- Attachment #2: what-line.patch --]
[-- Type: text/x-patch, Size: 2028 bytes --]

commit e678a23ee1b0864f76c2d91d4f354866dcd1199f
Author: Lars Brinkhoff <lars@nocrew.org>
Date:   Tue Jan 2 09:06:13 2024 +0100

    Fix what-page.

diff --git a/lisp/textmodes/page.el b/lisp/textmodes/page.el
index e8621ee0383..afbc614770e 100644
--- a/lisp/textmodes/page.el
+++ b/lisp/textmodes/page.el
@@ -159,21 +159,25 @@ count-lines-page
              total before after)))
 
 (defun page--what-page ()
-  "Return a list of the page and line number of point."
+  "Return a list of the page number of point, and the line number
+within that page."
   (save-restriction
     (widen)
     (save-excursion
       (let ((count 1)
-            (opoint (point)))
+            (opoint (point))
+            (oline (line-number-at-pos (point))))
         (goto-char (point-min))
         (while (re-search-forward page-delimiter opoint t)
           (when (= (match-beginning 0) (match-end 0))
             (forward-char))
           (setq count (1+ count)))
-        (list count (line-number-at-pos opoint))))))
+        (list count
+              (1+ (- oline (line-number-at-pos (point)))))))))
 
 (defun what-page ()
-  "Print page and line number of point."
+  "Display the page number of point, and the line number within
+that page."
   (interactive)
   (apply #'message (cons "Page %d, line %d" (page--what-page))))
 
diff --git a/test/lisp/textmodes/page-tests.el b/test/lisp/textmodes/page-tests.el
index f3a2c5fbe00..617b59a54fb 100644
--- a/test/lisp/textmodes/page-tests.el
+++ b/test/lisp/textmodes/page-tests.el
@@ -106,10 +106,14 @@ page-tests-what-page
     (insert "foo\n\f\nbar\n\f\nbaz")
     (goto-char (point-min))
     (should (equal (page--what-page) '(1 1)))
+    (forward-char)
+    (should (equal (page--what-page) '(1 1)))
     (forward-page)
+    (should (equal (page--what-page) '(2 1)))
+    (next-line)
     (should (equal (page--what-page) '(2 2)))
     (forward-page)
-    (should (equal (page--what-page) '(3 4)))))
+    (should (equal (page--what-page) '(3 1)))))
 
 
 ;;; page-tests.el ends here