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bug#8627: 24.0.50: cursor property behaves irregularly in before-strings
From: |
Alp Aker |
Subject: |
bug#8627: 24.0.50: cursor property behaves irregularly in before-strings |
Date: |
Fri, 06 May 2011 17:17:16 -0400 (EDT) |
But if the before-string contains a newline, the cursor property
appears to be ignored.
I will take a look at fixing this, but can you show a real-life use
case where this is needed?
I ran into the need while working on this package:
emacswiki.org/emacs/FillColumnIndicator
It shades the area past the fill column by putting overlays on newlines
(if you look at the screenshot it'll be obvious how it works). In a few
edge cases it would be useful to be able to display a newline that's not
part of the buffer content. For example, if the last line of the buffer
doesn't end in a newline, then no fill-column shading appears on that line
(since there's no newline to propertize). I'd like to put an overlay at
point-max with an after-string containing a propertized newline character,
so that the fill-column shading can appear on the last line of the buffer.
But I can't do so, because the newline in the after-string causes any
cursor property in it to be ignored, and so cursor motion at the end of
the buffer becomes deranged. (Display strings won't do here, because I
don't want to replace the display of any characters in the buffer.)
Does that qualify as a use case?
I might as well also mention, at least for the record, another (minor)
issue with cursor properties in before-strings that I came across: If the
position with the cursor property is out of sight because of horizontal
scrolling, then the property is ignored, even when auto-hscroll-mode is
enabled. Perhaps it would make more sense to respect the cursor property
when auto-hscroll-mode is non-nil, and adjust hscrolling to bring the
requested cursor position into view?
Here's a test case:
(progn
(setq auto-hscroll-mode t)
;; A line of text, moving to the end of which will trigger hscrolling.
(insert (make-string (+ hscroll-margin (window-width) 5) ?X))
(setq m (point-marker))
(insert "\n\n")
(setq o (make-overlay (1- (point)) (point)))
;; Request that cursor be at bol, but make the before-string long
;; enough that if the cursor property is ignored we won't return from
;; hscrolling.
(overlay-put o
'before-string
(concat
(propertize " " 'cursor 1)
(make-string (window-width) 32)))
(goto-char m)
(redisplay)
(forward-line 1))
After evaluation the cursor will be at the end of the before-string,
rather than at the requested position. (This happens with 22 and 23 as
well.)