Re: anomalies of overlays and before-string and display properties

[Joe Wells]

Can anyone else reproduce these issues with the code I supplied?  I
haven't heard any reply.  Does that mean I'm the only one these things
happen to?

Joe

Joe Wells <jbw@macs.hw.ac.uk> writes:

> By the way, with one exception, these problems also occur with
> after-string properties.
>
> The exception is that the overlay's mouse-face property does correctly
> cover both the overlays display and after-string properties.  This is
> more evidence that not covering the before-string property is a bug.
>
> Strangely, the after-string also “inherits” face attributes from the
> character after the beginning of the overlay, not the character just
> before the _end_ of the overlay.  This is more evidence that this is a
> bug and not a feature.
>
> Joe
>
> Joe Wells <jbw@macs.hw.ac.uk> writes:
>
>> There are a number of strange anomalies (some clearly bugs) in the
>> behavior of overlays and before-string and display properties.
>>
>> 1. Faces on a display property on a before-string behave differently
>>    depending on where the display property is in the before-string.
>>    For a display property at the beginning of the before-string, its
>>    face is used and the before-string's face is ignored (I think this
>>    is correct).  For a display property not at the beginning of the
>>    before-string, its face is completely ignored, and the face of the
>>    before-string is used instead.  This is fairly clearly a bug.
>>
>> 2. When a substring of a before-string beginning at offset O has a
>>    display property which is a string S, the first O characters of S
>>    are not displayed.  If S is not at least O+1 characters long, then
>>    disastrous things start to happen.  This is clearly a bug.
>>
>> 3. The before-string somehow “inherits” face attributes from the face
>>    of the character that follows the start of the overlay.  (If the
>>    overlay is of length zero, this character is not even in the
>>    overlay.  See the recent discussion of how this problem is
>>    affecting linum.el.)  This means that in practice a before-string
>>    needs to use completely specified faces, which is obviously a real
>>    pain.
>>
>> 4. The display property of an overlay somehow “inherits” face
>>    attributes from the face of the character that follows the start of
>>    the overlay.  This has similar disadvantages to anomaly #3
>>    mentioned above.
>>
>> 5. The help-echo and mouse-face properties of an overlay with both a
>>    before-string and a display property only affect the material
>>    displayed by the overlay's display property.  One can work around
>>    the issue by copying these properties to the various display
>>    properties inside the before-string; however, this workaround is a
>>    pain and in the case of mouse-face it doesn't get the entire
>>    overlay highlighted at once but instead only the pieces are
>>    highlighted one at a time.  It would be nice to be able to set a
>>    single help-echo or a single mouse-face property that would affect
>>    the _entire_ overlay.
>>
>> You can reproduce all of these anomalies with this function:
>>
>>   (defun illustrate-anomalies ()
>>     (let ((s #1=#("\\abcd{VWXYZ}"
>>                   0 5 (face (:foreground "Purple" :background "yellow"))
>>                   5 12
>>                   (face
>>                    (:foreground
>>                     "DarkOliveGreen"
>>                     :weight bold :slant oblique :height 0.8))))
>>           (props
>>            '(help-echo
>>              #1#
>>              ;;face (:slant italic :foreground "red")
>>              display "]"
>>              before-string
>>              #("  "
>>                0 1
>>                (display
>>                 #("|["
>>                   0 2 (;; help-echo #1#
>>                        face #2=(:strike-through t :background "white")))
>>                 ;; help-echo #1#
>>                 face #3=(:underline t))
>>                1 2
>>                (display
>>                 #("||VWXYZ"
>>                   0 7 (;; help-echo #1#
>>                        ;; mouse-face (:background "darkseagreen2")
>>                        face #2#))
>>                 ;; help-echo #1#
>>                 face #3#))
>>              mouse-face (:background "darkseagreen2")))
>>           (buf (get-buffer-create "xyzzy")))
>>       (with-current-buffer buf
>>         (display-buffer buf)
>>         (erase-buffer)
>>         (dolist (o (overlays-in (point-min) (point-max)))
>>           (delete-overlay o))
>>         (insert s)
>>         (let ((o (make-overlay (point-min) (point-max))))
>>           (while props
>>             (overlay-put o (car props) (cadr props))
>>             (setq props (nthcdr 2 props)))))))
>>
>> This example is derived from some work where I was trying to get
>> AUCTeX's folding mode to show the fontified and latex-previewed
>> contents of macro arguments.
>>
>> I hope this problem report is useful.
>>
>> Joe
>>
>> ======================================================================
>> In GNU Emacs 22.1.1 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
>>  of 2007-06-27 on artemis
>> Windowing system distributor `The X.Org Foundation', version 11.0.70000000
>> configured using `configure  '--prefix=/home/jbw/local2' '--enable-debug' 
>> '--disable-nls' '--with-x-toolkit=gtk' 'CFLAGS=-O0 -g3 -ggdb''
>>
>> Important settings:
>>   value of $LC_ALL: nil
>>   value of $LC_COLLATE: nil
>>   value of $LC_CTYPE: en_US.UTF-8
>>   value of $LC_MESSAGES: nil
>>   value of $LC_MONETARY: nil
>>   value of $LC_NUMERIC: nil
>>   value of $LC_TIME: jbw
>>   value of $LANG: nil
>>   locale-coding-system: utf-8
>>   default-enable-multibyte-characters: t
>>
>> Minor modes in effect:
>>   outline-minor-mode: t
>>   desktop-save-mode: t
>>   url-handler-mode: t
>>   tooltip-mode: t
>>   mouse-wheel-mode: t
>>   file-name-shadow-mode: t
>>   global-font-lock-mode: t
>>   font-lock-mode: t
>>   blink-cursor-mode: t
>>   unify-8859-on-encoding-mode: t
>>   utf-translate-cjk-mode: t
>>   auto-compression-mode: t
>>   temp-buffer-resize-mode: t
>>   size-indication-mode: t
>>   line-number-mode: t
>>   transient-mark-mode: t