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From: | Dmitry Gutov |
Subject: | bug#13743: 24.2.93; Segmentation fault when trying to [s]teal a file opened elsewhere |
Date: | Mon, 25 Feb 2013 09:52:24 +0400 |
User-agent: | Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130215 Thunderbird/17.0.3 |
On 24.02.2013 19:50, Eli Zaretskii wrote:
Date: Sun, 24 Feb 2013 19:28:32 +0400 From: Dmitry Gutov <dgutov@yandex.ru> CC: Stefan Monnier <monnier@iro.umontreal.ca>, 13743@debbugs.gnu.orgHow 'bout moving the if (BUFFERP (object)) modify_region (object, start, end); earlier in the function. Something like the patch below.This will (falsely, AFAIU) tell us that the region is about to be modified when we return at the point marked below:I tried the patches, and both seem to work fine so far. If you could explain the practical implications of the drawback in Stefan's patch you're describing here, I'll try to test for that, too.You need to simulate the situation which causes us to return here:/* If this interval already has the properties, we can skip it. */ if (interval_has_all_properties (properties, i)) { ptrdiff_t got = (LENGTH (i) - (s - i->position)); if (got >= len) RETURN_UNGCPRO (Qnil); <<<<<<<<<<<<<<<<<<<<<<<<<<<This condition means that we find an interval which already has the property we are trying to add, and that interval's length is at least as large as the distance between START and END. The simplest thing to try reproducing this would be to call add-text-properties with the property that is already somewhere in the buffer and with START and END that belong to the buffer region with this property. I hope this will show you what happens.
Thanks.
The manifestation of the problem will be that modify_region will be called in this case, although we don't actually modify anything. You will probably see the "modified" indicator on the mode line, something that shouldn't have happened.
That is indeed what happens. OTOH, the existing behavior in this area is rather messy anyway:a) If START equals to the beginning of the region with the same property, the buffer is marked modified anyway (even though nothing changes from the observer's point of view).
So, the trivial example of repeating an `add-text-properties' call with the same arguments in a previously unpropertized buffer will mark it as modified every time.
b) This probably has something to do with internal representation, but even having the same property span before START is not a safe bet:
1. Create a new file with a line of text in it, preferably without spaces, to see face changes easily
2. Save it, disable font-lock-mode. 3. Evaluate: (add-text-properties 1 6 '(face font-lock-constant-face)) => modified save (add-text-properties 2 6 '(face font-lock-constant-face)) => unmodified (add-text-properties 2 7 '(face font-lock-constant-face)) => modified save (add-text-properties 2 6 '(face font-lock-constant-face)) => unmodified - optional step (add-text-properties 2 7 '(face font-lock-constant-face)) => modified(!) - even though 1 still has the same face - you can save and repeat this step indefinitely
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