Reintroduce support for `adaptive-fill-regexp' in paragraphs and comments

* lisp/org.el (org-adaptive-fill-function, org-fill-paragraph): Add
  support for `adaptive-fill-regexp' in paragraphs and comments.
* testing/lisp/test-org.el: Add tests.

lisp/org.el

@@ -22113,7 +22113,8 @@ hierarchy of headlines by UP levels before marking the subtree."
 (defun org-adaptive-fill-function ()
   "Compute a fill prefix for the current line.
 Return fill prefix, as a string, or nil if current line isn't
-meant to be filled."
+meant to be filled.  For convenience, if `adaptive-fill-regexp'
+matches in paragraphs or comments, use it."
   (let (prefix)
     (catch 'exit
       (when (derived-mode-p 'message-mode)
@@ -22137,7 +22138,15 @@ meant to be filled."
 	      (post-affiliated (org-element-property :post-affiliated element)))
 	 (unless (and post-affiliated (< p post-affiliated))
 	   (case type
-	     (comment (looking-at "[ \t]*# ?") (match-string 0))
+	     (comment
+	      (save-excursion
+		(beginning-of-line)
+		(looking-at "[ \t]*#")
+		(goto-char (match-end 0))
+		(let ((comment-prefix (match-string 0)))
+		  (if (looking-at adaptive-fill-regexp)
+		      (concat comment-prefix (match-string 0))
+		    comment-prefix))))
 	     (footnote-definition "")
 	     ((item plain-list)
 	      (make-string (org-list-item-body-column
@@ -22146,15 +22155,17 @@ meant to be filled."
 			   ? ))
 	     (paragraph
 	      ;; Fill prefix is usually the same as the current line,
-	      ;; except if the paragraph is at the beginning of an item.
+	      ;; unless the paragraph is at the beginning of an item.
 	      (let ((parent (org-element-property :parent element)))
-		(cond ((eq (org-element-type parent) 'item)
-		       (make-string (org-list-item-body-column
-				     (org-element-property :begin parent))
-				    ? ))
-		      ((save-excursion (beginning-of-line) (looking-at "[ \t]+"))
-		       (match-string 0))
-		      (t  ""))))
+		(save-excursion
+		  (beginning-of-line)
+		  (cond ((eq (org-element-type parent) 'item)
+			 (make-string (org-list-item-body-column
+				       (org-element-property :begin parent))
+				      ? ))
+			((looking-at adaptive-fill-regexp) (match-string 0))
+			((looking-at "[ \t]+") (match-string 0))
+			(t  "")))))
 	     (comment-block
 	      ;; Only fill contents if P is within block boundaries.
 	      (let* ((cbeg (save-excursion (goto-char post-affiliated)
@@ -22297,13 +22308,17 @@ a footnote definition, try to fill the first paragraph within."
 				(1- (line-beginning-position))
 			      (skip-chars-backward " \r\t\n")
 			      (line-end-position)))))
-		 ;; Do not fill comments when at a blank line or at
-		 ;; affiliated keywords.
-		 (let ((fill-prefix (save-excursion
-				      (beginning-of-line)
-				      (looking-at "[ \t]*#")
-				      (concat (match-string 0) " "))))
-		   (when (> end begin)
+		 ;; Do not fill comments when at a blank line.
+		 (when (> end begin)
+		   (let ((fill-prefix
+			  (save-excursion
+			    (beginning-of-line)
+			    (looking-at "[ \t]*#")
+			    (let ((comment-prefix (match-string 0)))
+			      (goto-char (match-end 0))
+			      (if (looking-at adaptive-fill-regexp)
+				  (concat comment-prefix (match-string 0))
+				(concat comment-prefix " "))))))
 		     (save-excursion
 		       (fill-region-as-paragraph begin end justify))))))
 	     t))

testing/lisp/test-org.el

@@ -176,6 +176,14 @@
 	      (narrow-to-region 1 8)
 	      (org-fill-paragraph)
 	      (buffer-string)))))
+  ;; Handle `adaptive-fill-regexp' in paragraphs.
+  (should
+   (equal "> a b"
+	  (org-test-with-temp-text "> a\n> b"
+	    (let ((fill-column 5)
+		  (adaptive-fill-regexp "[ \t]*>+[ \t]*"))
+	      (org-fill-paragraph)
+	      (buffer-string)))))
   ;; Special case: Fill first paragraph when point is at an item or
   ;; a plain-list or a footnote reference.
   (should
@@ -225,6 +233,14 @@
 	    (let ((fill-column 20))
 	      (org-fill-paragraph)
 	      (buffer-string)))))
+  ;; Handle `adaptive-fill-regexp' in comments.
+  (should
+   (equal "# > a b"
+	  (org-test-with-temp-text "# > a\n# > b"
+	    (let ((fill-column 20)
+		  (adaptive-fill-regexp "[ \t]*>+[ \t]*"))
+	      (org-fill-paragraph)
+	      (buffer-string)))))
   ;; Do nothing at affiliated keywords.
   (org-test-with-temp-text "#+NAME: para\nSome\ntext."
     (let ((fill-column 20))
@@ -255,6 +271,15 @@
 	      (end-of-line)
 	      (org-auto-fill-function)
 	      (buffer-string)))))
+  ;; Auto fill paragraph when `adaptive-fill-regexp' matches.
+  (should
+   (equal "> 12345\n> 7890"
+	  (org-test-with-temp-text "> 12345 7890"
+	    (let ((fill-column 5)
+		  (adaptive-fill-regexp "[ \t]*>+[ \t]*"))
+	      (end-of-line)
+	      (org-auto-fill-function)
+	      (buffer-string)))))
   ;; Auto fill comments.
   (should
    (equal "  # 12345\n  # 7890"
@@ -263,6 +288,15 @@
 	      (end-of-line)
 	      (org-auto-fill-function)
 	      (buffer-string)))))
+  ;; Auto fill comments when `adaptive-fill-regexp' matches.
+  (should
+   (equal "  # > 12345\n  # > 7890"
+	  (org-test-with-temp-text "  # > 12345 7890"
+	    (let ((fill-column 10)
+		  (adaptive-fill-regexp "[ \t]*>+[ \t]*"))
+	      (end-of-line)
+	      (org-auto-fill-function)
+	      (buffer-string)))))
   ;; A hash within a line isn't a comment.
   (should-not
    (equal "12345 # 7890\n# 1"