org-agenda: Refactor org-agenda-overriding-header code

* lisp/org-agenda.el (org-agenda--insert-overriding-header): Add macro.
(org-agenda-list)
(org-search-view)
(org-todo-list)
(org-tags-view): Use macro.
(org-agenda-overriding-header): Update docstring.

* etc/ORG-NEWS: Explain that header can be disabled with empty string.

Replace org-agenda-overriding-header tests in these four functions with
calls to a macro, eliminating the duplicate code.  Also, disable the
header when the variable is set to the empty string.

etc/ORG-NEWS

@@ -135,6 +135,10 @@ See docstring for details.
 =org-agenda-tags-column= can now be set to =auto=, which will
 automatically align tags to the right edge of the window.  This is now
 the default setting.
+**** Disable =org-agenda-overriding-header= by setting to empty string
+
+The =org-agenda-overriding-header= inserted into agenda views can now be
+disabled by setting it to an empty string.
 
 *** New value for ~org-publish-sitemap-sort-folders~
 

lisp/org-agenda.el

@@ -2064,6 +2064,22 @@ works you probably want to add it to `org-agenda-custom-commands' for good."
 	(setcdr ass (cdr entry))
       (push entry org-agenda-custom-commands))))
 
+(defmacro org-agenda--insert-overriding-header (default)
+  "Insert header into agenda view depending on value of `org-agenda-overriding-header'.
+If the empty string, don't insert a header.  If any other string,
+insert it as a header.  If nil, insert DEFAULT, which should
+evaluate to a string."
+  (declare (debug (form)) (indent defun))
+  `(pcase org-agenda-overriding-header
+     ("" nil)  ; Don't insert a header if set to empty string
+     ;; Insert user-specified string
+     ((pred stringp) (insert
+		      (org-add-props (copy-sequence org-agenda-overriding-header)
+			  nil 'face 'org-agenda-structure)
+		      "\n"))
+     ;; When nil, make string automatically and insert it
+     ((pred null) (insert ,default))))
+
 ;;; Define the org-agenda-mode
 
 (defvar org-agenda-mode-map (make-sparse-keymap)
@@ -4155,10 +4171,8 @@ items if they have an hour specification like [h]h:mm."
 	       (w1 (org-days-to-iso-week d1))
 	       (w2 (org-days-to-iso-week d2)))
 	  (setq s (point))
-	  (if org-agenda-overriding-header
+	  (org-agenda--insert-overriding-header
-	      (insert (org-add-props (copy-sequence org-agenda-overriding-header)
+	    (concat (org-agenda-span-name span)
-			  nil 'face 'org-agenda-structure) "\n")
-	    (insert (org-agenda-span-name span)
 		    "-agenda"
 		    (if (< (- d2 d1) 350)
 			(if (= w1 w2)
@@ -4576,9 +4590,8 @@ in `org-agenda-text-search-extra-files'."
 			(goto-char (1- end))))))))))
 	(setq rtn (nreverse ee))
 	(setq rtnall (append rtnall rtn)))
-      (if org-agenda-overriding-header
+      (org-agenda--insert-overriding-header
-	  (insert (org-add-props (copy-sequence org-agenda-overriding-header)
+	(with-temp-buffer
-		      nil 'face 'org-agenda-structure) "\n")
 	  (insert "Search words: ")
 	  (add-text-properties (point-min) (1- (point))
 			       (list 'face 'org-agenda-structure))
@@ -4594,7 +4607,8 @@ Press `\\[org-agenda-manipulate-query-add]', \
 `\\[org-agenda-manipulate-query-subtract-re]' to add/sub regexp, \
 `\\[universal-argument] \\[org-agenda-redo]' to edit\n"))
 	    (add-text-properties pos (1- (point))
-			       (list 'face 'org-agenda-structure))))
+				 (list 'face 'org-agenda-structure)))
+	  (buffer-string)))
       (org-agenda-mark-header-line (point-min))
       (when rtnall
 	(insert (org-agenda-finalize-entries rtnall 'search) "\n"))
@@ -4672,9 +4686,8 @@ for a keyword.  A numeric prefix directly selects the Nth keyword in
 	  (org-check-agenda-file file)
 	  (setq rtn (org-agenda-get-day-entries file date :todo))
 	  (setq rtnall (append rtnall rtn))))
-      (if org-agenda-overriding-header
+      (org-agenda--insert-overriding-header
-	  (insert (org-add-props (copy-sequence org-agenda-overriding-header)
+        (with-temp-buffer
-		      nil 'face 'org-agenda-structure) "\n")
 	  (insert "Global list of TODO items of type: ")
 	  (add-text-properties (point-min) (1- (point))
 			       (list 'face 'org-agenda-structure
@@ -4696,7 +4709,8 @@ for a keyword.  A numeric prefix directly selects the Nth keyword in
 		      (insert " " s))
 		    kwds))
 	    (insert "\n"))
-	(add-text-properties pos (1- (point)) (list 'face 'org-agenda-structure)))
+	  (add-text-properties pos (1- (point)) (list 'face 'org-agenda-structure))
+	  (buffer-string)))
       (org-agenda-mark-header-line (point-min))
       (when rtnall
 	(insert (org-agenda-finalize-entries rtnall 'todo) "\n"))
@@ -4774,9 +4788,8 @@ The prefix arg TODO-ONLY limits the search to TODO entries."
 					   matcher
 					   org--matcher-tags-todo-only))
 		  (setq rtnall (append rtnall rtn))))))))
-      (if org-agenda-overriding-header
+      (org-agenda--insert-overriding-header
-	  (insert (org-add-props (copy-sequence org-agenda-overriding-header)
+        (with-temp-buffer
-		      nil 'face 'org-agenda-structure) "\n")
 	  (insert "Headlines with TAGS match: ")
 	  (add-text-properties (point-min) (1- (point))
 			       (list 'face 'org-agenda-structure
@@ -4791,7 +4804,8 @@ The prefix arg TODO-ONLY limits the search to TODO entries."
 		     "Press `\\[universal-argument] \\[org-agenda-redo]' \
 to search again with new search string\n")))
 	  (add-text-properties pos (1- (point))
-			     (list 'face 'org-agenda-structure)))
+			       (list 'face 'org-agenda-structure))
+	  (buffer-string)))
       (org-agenda-mark-header-line (point-min))
       (when rtnall
 	(insert (org-agenda-finalize-entries rtnall 'tags) "\n"))
@@ -4815,8 +4829,11 @@ used by user-defined selections using `org-agenda-skip-function'.")
 
 (defvar org-agenda-overriding-header nil
   "When set during agenda, todo and tags searches it replaces the header.
-This variable should not be set directly, but custom commands can bind it
+If an empty string, no header will be inserted.  If any other
-in the options section.")
+string, it will be inserted as a header.  If nil, a header will
+be generated automatically according to the command.  This
+variable should not be set directly, but custom commands can bind
+it in the options section.")
 
 (defun org-agenda-skip-entry-if (&rest conditions)
   "Skip entry if any of CONDITIONS is true.