Revert mark-paragraph change and add tests

* lisp/textmodes/paragraphs.el (mark-paragraph): Revert
eb090f65ceb0ae8a90829e911694348583135ba5 (bug#45318).  This restores
the behaviour from Emacs 27 -- further work is needed on this patch.

1 files changed, 23 insertions, 40 deletions

diff --git a/lisp/textmodes/paragraphs.el b/lisp/textmodes/paragraphs.el
index 217ae10fe4d..96edfd6de36 100644
--- a/lisp/textmodes/paragraphs.el
+++ b/lisp/textmodes/paragraphs.el
@@ -371,50 +371,33 @@ See `forward-paragraph' for more information."
 
 (defun mark-paragraph (&optional arg allow-extend)
   "Put point at beginning of this paragraph, mark at end.
-The paragraph marked is the one that contains point or follows
-point.
+The paragraph marked is the one that contains point or follows point.
 
-With argument ARG, puts mark at the end of this or a following
-paragraph, so that the number of paragraphs marked equals ARG.
+With argument ARG, puts mark at end of a following paragraph, so that
+the number of paragraphs marked equals ARG.
 
-If ARG is negative, point is put at the end of this paragraph,
-mark is put at the beginning of this or a previous paragraph.
+If ARG is negative, point is put at end of this paragraph, mark is put
+at beginning of this or a previous paragraph.
 
 Interactively (or if ALLOW-EXTEND is non-nil), if this command is
-repeated or (in Transient Mark mode) if the mark is active, it
-marks the next ARG paragraphs after the region already marked.
-This also means when activating the mark immediately before using
-this command, the current paragraph is only marked from point."
-  (interactive "P\np")
-  (let ((numeric-arg (prefix-numeric-value arg)))
-    (cond ((zerop numeric-arg))
-	  ((and allow-extend
-		(or (and (eq last-command this-command) mark-active)
-		    (region-active-p)))
-	   (if arg
-	       (setq arg numeric-arg)
-	     (if (< (mark) (point))
-		 (setq arg -1)
-	       (setq arg 1)))
-	   (set-mark
-	    (save-excursion
-	      (goto-char (mark))
-	      (forward-paragraph arg)
-	      (point))))
-	  ;; don't activate the mark when at eob
-	  ((and (eobp) (> numeric-arg 0)))
-	  (t
-	   (unless (save-excursion
-		     (forward-line 0)
-		     (looking-at  paragraph-start))
-	     (backward-paragraph (cond ((> numeric-arg 0) 1)
-                                       ((< numeric-arg 0) -1)
-                                       (t 0))))
-	   (push-mark
-	    (save-excursion
-	      (forward-paragraph numeric-arg)
-	      (point))
-            t t)))))
+repeated or (in Transient Mark mode) if the mark is active,
+it marks the next ARG paragraphs after the ones already marked."
+  (interactive "p\np")
+  (unless arg (setq arg 1))
+  (when (zerop arg)
+    (error "Cannot mark zero paragraphs"))
+  (cond ((and allow-extend
+	      (or (and (eq last-command this-command) (mark t))
+		  (and transient-mark-mode mark-active)))
+	 (set-mark
+	  (save-excursion
+	    (goto-char (mark))
+	    (forward-paragraph arg)
+	    (point))))
+	(t
+	 (forward-paragraph arg)
+	 (push-mark nil t t)
+	 (backward-paragraph arg))))
 
 (defun kill-paragraph (arg)
   "Kill forward to end of paragraph.