bug#17824: 24.4.50; Cursor interferes with underline and bold of overlapping overlays.

[Keith David Bershatsky]

When the cursor touches two (2) overlapping overlays, an incorrect display 
occurs under the following example:

* Both overlays contain the same priority, or no assigned priority.

* First overlay: . . . 'face '(:foreground "red" :weight bold)

* Second overlay . . . 'face '(:underline "yellow" :weight normal)

[The same result also happens if the bolded foreground face is a glpyh in the 
`buffer-display-table`, and where only one (1) overlay contains a *normal* 
weight underline.  So, this issue does not appear to be exclusive to only the 
presence of overlapping overlays.]

The desired result is a bold foreground for the text, and a normal weight 
underline.  That result can be achieved if the cursor does not touch the 
overlapping overlays.  Once the cursor has touched the overlapping overlays, 
however, the underline takes on a *bold* visual attribute.  This improper 
*bold* attribute may extend for the entire length of the overlay, depending 
upon which direction the cursor is moving and other overlays that may be 
present.

I was not able to correct this situation by setting priorities.  In my various 
tests, setting priorities only served to choose one overlay over the other -- 
i.e., setting priorities do not permit the overlays to co-exist in harmony.

The thread that I opened on Stackoverflow contains some screen shots and a 
recipe to reproduce the error.  It is not necessary to use flyspell or 
hl-line-mode to reproduce the error, that was simply the example I chose 
because it is the one where I always see the error.  Perhaps the reason why the 
initial test by @Drew may not have yielded the same result is that his cursor 
was not touching "mal-normal" -- had his cursor touched that section of the 
buffer, the same result as I experienced may have occurred.  I also use OSX, 
but it may not be an OS specific issue.

http://stackoverflow.com/questions/24313953/overlays-how-to-prevent-bold-faces-from-trumping-non-bold-faces

Here is the recipe -- just adjust the path to the `ispell-program-name`:

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;; GNU Emacs 24.4.50.1 (x86_64-apple-darwin10.8.0,
;; NS appkit-1038.36 Version 10.6.8 (Build 10K549)) of 2014-06-01 on MP.local

(set-face-attribute 'default nil
  :background "black" :foreground "white" :font "Courier" :height 180)

(tool-bar-mode -1)

(require 'ispell)

(require 'flyspell)

(setq-default ispell-program-name
    "/Users/HOME/.0.data/.0.emacs/elpa/bin/aspell")

(custom-set-faces
  '(flyspell-incorrect ((t (:foreground "yellow" :weight bold ))))
  '(highlight ((t (:underline "red" :weight normal)))))

(defun zoom ()
(interactive)
  (setq buffer-face-mode-face `(:height 575))
  (buffer-face-mode 1))

(defun test-number-one ()
(interactive)
  (switch-to-buffer (get-buffer-create "test-number-ONE"))
  (zoom)
  (turn-on-flyspell)
  (setq flyspell-mark-duplications-flag nil)
  (setq flyspell-duplicate-distance 0)
  (hl-line-mode 1)
  (insert
    "This is `test-number-one`."
    "\n"
    "\n"
    "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ"
    "\n"
    "\n"
    "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ"))

(defun test-number-two ()
(interactive)
  (switch-to-buffer (get-buffer-create "test-number-TWO"))
  (zoom)
  (hl-line-mode 1)
  (insert
    "This is `test-number-two`."
    "\n"
    "\n"
    "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ"
    "\n"
    "\n"
    "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ"))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Thanks,

Keith

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In GNU Emacs 24.4.50.1 (x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 
10.6.8 (Build 10K549))
 of 2014-06-01 on MP.local
Repository revision: 117215 lekktu@gmail.com-20140601162519-4dacx2w0ak528z2r
Windowing system distributor `Apple', version 10.3.1038
Configured using:
 `configure --with-ns'

Configured features:
ACL LIBXML2 ZLIB

Important settings:
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Major mode: Fundamental

Minor modes in effect:
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Recent input:
<escape> x r e p o r t - e m a c s - b u g <return>

Recent messages:
[k]ill or [s]ave draft?
Loading msgdb for 
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Saving file /Users/HOME/.0.data/.0.emacs/.scratch...
Wrote /Users/HOME/.0.data/.0.emacs/.scratch
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