Subject: bug#20153: 24.4.91; destructive add-face-text-property and string deep copying

From: Lars Ingebrigtsen <[email-masked]>
Date: Wed, 09 Oct 2019 19:45:54 +0200

Eli Zaretskii <[email-masked]> writes:

>> Instead I've now changed add_properties (and add_text_properties_1) to
>> take a bool parameter to say whether they're allowed to be destructive
>> or not, and make the add-face-text-property call that with false as the
>> parameter if the object is a string.  This fixes the test case for me
>> and should hopefully have no measurable performance impact.
>
> Isn't that a backward-incompatible change?

It is, but the previous behaviour was a bug.  If you have a copy of a
string and modify the copy, the original string shouldn't change.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no