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bug#18285: 24.3.92; A combination of `display' on text and `invisible' a

From: Dmitry Gutov
Subject: bug#18285: 24.3.92; A combination of `display' on text and `invisible' and `before/after-string' leads to the before/after string being displayed twice
Date: Thu, 21 Aug 2014 18:07:07 +0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0

On 08/18/2014 07:07 PM, Eli Zaretskii wrote:

Believe it or not, but this is how the code was written 14 years ago,
although perhaps this particular consequence wasn't intended.  But it
follows logically from how the display engine works.

I can believe it all right. I guess the question is, could there be a modification of the current logic that would preserve most of the current behavior, except for the weird situations like this one.

If not, that's all right by me. The workaround of replacing `before-string' + `invisible' with just `display' seems to function just fine so far. For some reason, Nikolaj opted to render the completion tooltip in Company with the former option, so I tried not to change it too much. Maybe that worked around some bugs in older Emacs, which we don't support anymore.

The fundamental issue here is that the 'invisible' property makes all
the character positions between the start and the end of the overlay
indistinguishable.  Therefore, the display engine considers the
'before-string' and 'after-string' of an overlay that spans invisible
text to be applicable to both the start and the end of the overlay,
something it wouldn't do if the 'invisible' property were not present.

Hmm. Maybe the fix could be to make the `invisible' property disable `display': as long as former is present, the latter won't work.

After all, that was the intention behind the code I encountered this bug in. And with the current logic, like you say, if `display' is set, `invisible' is redundant.

I think it's not worth to try to fix this (by complicating the heck
out of the display engine) on the account of this use case.

Maybe so, but see above.

My crystal ball says ...
... IOW, without the 'invisible' property getting in the way,
the 'before-string' is displayed before the display property, and
the 'after-string' is displayed after it.

Yes, sure. I just meant that the bug is the same with `invisible' on.

Btw, there was a discussion of a similar issue starting at


It was inconclusive.

Thanks. That looks very much like a bug as well, though maybe again, too expensive to fix. FWIW, for that issue, if myov2 has higher priority than myov1 (if only by virtue of being inside and shorter), I'd display just "STRING2" ("STRING1" would not be visible at all). But that's just going by logic; maybe there's a use case that would break.

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