bug#24073: 24.5; outline-on-heading-p sees any invisible text property as outline inviisble

[Paul Rankin]

When attempting to use `outline' to collapse a heading that begins with a 
character with any invisible text property, the heading is mistakenly treated 
as invisible, when only a heading with the `outline' invisible text property 
should be considered invisible (i.e. collapsed).

To reproduce:

1. emacs -Q
2. insert ";;; heading"
3. M-: (outline-on-heading-p)
    => t
4. C-a
5. M-: (put-text-property (point) (1+ (point)) 'invisible 'foo)
6. M-; (outline-on-heading-p)
    => nil

Expected results:

(outline-on-heading-p)
    => t

Actual results:

(outline-on-heading-p)
    => nil

Solution:

The function outline-on-heading-p checks bolp for an invisible property, but 
not specifically the `outline' invisible property:

    (defun outline-on-heading-p (&optional invisible-ok)
      "Return t if point is on a (visible) heading line.
    If INVISIBLE-OK is non-nil, an invisible heading line is ok too."
      (save-excursion
        (beginning-of-line)
        (and (bolp) (or invisible-ok (not (outline-invisible-p)))
               (looking-at outline-regexp))))

Instead, it should check for only the `outline' invisible text property:

    (defun outline-on-heading-p (&optional invisible-ok)
        "Return t if point is on a (visible) heading line.
    If INVISIBLE-OK is non-nil, an invisible heading line is ok too."
        (save-excursion
          (beginning-of-line)
          (and (bolp) (or invisible-ok (not (eq (outline-invisible-p) 
'outline)))
               (looking-at outline-regexp))))

-- 
Paul W. Rankin
www.paulwrankin.com