Re: make-overlay and endpoints
Hi Stephen
"Stephen J. Turnbull" <stephen(a)xemacs.org> writes:
Marcus Harnisch writes:
AFAIK, Emacs doesn't give you the choice of removing the overlay from
the buffer.
> In XEmacs 21.5.34 doing the same with an extent
> (start-closed/end-open) removes the extent from the buffer.
By default, and it doesn't delete the extent, it detaches it. (I
don't think Emacs implements detached overlays.) If you want the
extent to remain in the buffer, set the detachable property to nil.
If you're using the overlay library from fsf-compat, this might be a
bug in overlay emulation.
Regarding a potential issue in the overlay emulation I can look into
that. Thanks.
> “Deletion of a character on a side of a zero-length extent
whose
> corresponding endpoint is closed causes the extent to be detached if
> its `detachable' property is set; if the corresponding endpoint is
> open, the extent remains in the buffer, moving as necessary.”
>
> What exactly does “a character on a side” mean. I can only delete a
> character “at” the extent.
You may misunderstand the nature of character positions in Emacsen, I
suspect.
Not at all. I just found it very confusing that instead of using a
common "before pos"/"after pos", a rather more colloquial term was
used.
I don't understand what the practical problem you're
experiencing is,
so I doubt all this theoretical discussion is of much help (unless
maybe it will result in a bug report on fsf-compat). Sorry about
that, and feel free to follow up.
The practical problem is in the latest (ca 2012) version of psvn.el
which rightfully claims that #'svn-status-blame wouldn't work for
XEmacs. In contrast to the suspected (by its author) reason, it
happens that a zero-length extent is created at point (via
make-overlay), followed by #'delete-region starting at point. In
XEmacs the extent (and its begin-glyph) disappear. Presumably in Emacs
the corresponding overlay remains visible.
Swapping the two lines of code in psvn.el is trivial, but since the
existing code is meant to work in Emacs I figured this may point to a
compatibility issue.
Regards
Marcus
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