[PATCH] org.el: Fix newline at eob in org-insert-heading

[Leo Vivier <zaephon@gmail.com>]

* lisp/org.el (org-insert-heading): Check if narrowed before inserting
newline at eob

When narrowed into an org-buffer (e.g. when capturing), adding a new
heading with C-<return> or M-<return> on the last line of a
buffer (i.e. that not without a newline at the end) would result in
the insertion of a newline at the bottom of the narrowed capture
buffer.

- C-<return>: `org-insert-heading-respect-content'
- M-<return>: `org-meta-return'

Both functions use `org-insert-heading' in their definitions.

The problem is due to `eobp' returning t when point is on the last
character of the narrowed buffer (as explained in its docstring).
Since those `eobp' predicates in `org-insert-heading' are probably
there to ensure a newline at the end of the *file*, checking whether
we are at the end of the *widened* buffer prior to inserting the
newline fixes the problem.

The patch I'd originally submitted failed to address narrowed buffer
whose `(max-pos)` was also that of the widened buffer.  Rather than
using `(buffer-narrowed-p)`, I opted for a `(widen)` followed by
`(eobp)`.

TINYCHANGE
---
I was able to replicate the problem with `emacs -q`, so the problem
doesn't seem to come from custom options in my own setup. 

The problematic lines were inserted in the following commit:
b16feed40c7f519ada0cd9315251dcc257be31d2 .  Their goal was to C-<RET>
more predictable, and I don't think I've modified that behaviour in a
any way.

Let me know if you'd rather have me squash the changes.

 lisp/org.el | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index 7e74c2199..fef13f818 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -7542,8 +7542,9 @@ unconditionally."
       (unless (and blank? (org-previous-line-empty-p))
 	(org-N-empty-lines-before-current (if blank? 1 0)))
       (insert stars " ")
-      (when (and (eobp)
-                 (not (buffer-narrowed-p)))
+      (when (save-restriction
+              (widen)
+              (eobp))
         (save-excursion (insert "\n")))
       ;; When INVISIBLE-OK is non-nil, ensure newly created headline
       ;; is visible.
@@ -7572,15 +7573,17 @@ unconditionally."
 	       (when blank? (insert "\n"))
 	       (insert "\n" stars " ")
 	       (when (org-string-nw-p split) (insert split))
-	       (when (and (eobp)
-                          (not (buffer-narrowed-p)))
+	       (when (save-restriction
+                       (widen)
+                       (eobp))
                  (save-excursion (insert "\n")))))
 	    (t
 	     (end-of-line)
 	     (when blank? (insert "\n"))
 	     (insert "\n" stars " ")
-	     (when (and (eobp)
-                        (not (buffer-narrowed-p)))
+	     (when (save-restriction
+                       (widen)
+                       (eobp))
                (save-excursion (insert "\n"))))))
      ;; On regular text, turn line into a headline or split, if
      ;; appropriate.
-- 
2.20.1