org.el: New function org-delete-indentation

* org.el (org-delete-indentation): New function.
  (org-mode-map): Bind org-delete-indentation to M-^.
* test-org.el (test-org-delete-indentation): Test org-delete-indentation.
* ORG-NEWS: Add entry on org-delete-indentation.

etc/ORG-NEWS

@@ -376,6 +376,9 @@ for details.
 Calling ~org-edit-footnote-reference~ (C-c ') on a footnote reference
 allows to edit its definition, as long as it is not anonymous, in
 a dedicated buffer.  It works even if buffer is currently narrowed.
+*** New function ~org-delete-indentation~ bound to ~M-^~
+Work as ~delete-indentation~ unless at heading, in which case text is
+added to headline text.
 ** Miscellaneous
 *** Strip all meta data from ITEM special property
 ITEM special property does not contain TODO, priority or tags anymore.

lisp/org.el

@@ -19832,6 +19832,7 @@ boundaries."
 (org-defkey org-mode-map [remap comment-dwim] 'org-comment-dwim)
 (org-defkey org-mode-map [remap forward-paragraph] 'org-forward-paragraph)
 (org-defkey org-mode-map [remap backward-paragraph] 'org-backward-paragraph)
+(org-defkey org-mode-map "\M-^"     'org-delete-indentation)
 (org-defkey org-mode-map "\C-m"     'org-return)
 (org-defkey org-mode-map "\C-j"     'org-return-indent)
 (org-defkey org-mode-map "\C-c?"    'org-table-field-info)
@@ -21159,6 +21160,39 @@ This command does many different things, depending on context:
     (let ((org-note-abort t))
       (funcall org-finish-function))))
 
+(defun org-delete-indentation (&optional ARG)
+  "Join current line to previous and fix whitespace at join.
+
+If previous line is a headline add to headline title.  Otherwise
+the function calls `delete-indentation'.
+
+With argument, join this line to following line."
+  (interactive "*P")
+  (if (save-excursion
+	(if ARG (beginning-of-line)
+	  (forward-line -1))
+	(looking-at org-complex-heading-regexp))
+      ;; At headline.
+      (let ((tags-column (when (match-beginning 5)
+			   (save-excursion (goto-char (match-beginning 5))
+					   (current-column))))
+	    (string (concat " " (progn (when ARG (forward-line 1))
+				       (org-trim (delete-and-extract-region
+						  (line-beginning-position)
+						  (line-end-position)))))))
+	(unless (bobp) (delete-region (point) (1- (point))))
+	(goto-char (or (match-end 4)
+		       (match-beginning 5)
+		       (match-end 0)))
+	(skip-chars-backward " \t")
+	(save-excursion (insert string))
+	;; Adjust alignment of tags.
+	(when tags-column
+	  (org-align-tags-here (if org-auto-align-tags
+				   org-tags-column
+				 tags-column))))
+    (delete-indentation ARG)))
+
 (defun org-open-line (n)
   "Insert a new row in tables, call `open-line' elsewhere.
 If `org-special-ctrl-o' is nil, just call `open-line' everywhere."

testing/lisp/test-org.el

@@ -833,6 +833,36 @@
 
 ;;; Editing
 
+(ert-deftest test-org/delete-indentation ()
+  "Test `org-delete-indentation' specifications."
+  ;; Regular test.
+  (should (equal "foo bar"
+		(org-test-with-temp-text
+		    "foo \n bar<point>"
+		  (org-delete-indentation)
+		  (buffer-string))))
+  ;; With optional argument.
+  (should (equal "foo bar"
+		(org-test-with-temp-text
+		    "foo<point> \n bar"
+		  (org-delete-indentation t)
+		  (buffer-string))))
+  ;; At headline text should be appended to the headline text.
+  (should
+   (equal"* foo bar :tag:"
+	 (let (org-auto-align-tags)
+	   (org-test-with-temp-text
+	       "* foo :tag:\n bar<point>"
+	     (org-delete-indentation)
+	     (buffer-string)))))
+  (should
+   (equal "* foo bar :tag:"
+	  (let (org-auto-align-tags)
+	    (org-test-with-temp-text
+		"* foo <point>:tag:\n bar"
+	      (org-delete-indentation t)
+	      (buffer-string))))))
+
 (ert-deftest test-org/return ()
   "Test `org-return' specifications."
   ;; Regular test.