bug#56685: OBOE in string-truncate-left?

[Stephen Berman <stephen.berman@gmx.net>]

On Fri, 22 Jul 2022 16:33:07 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: stefan@marxist.se,  56685@debbugs.gnu.org
>> Date: Fri, 22 Jul 2022 14:35:02 +0200
>>
>> Currently, the result of applying string-truncate-left to STRING can be
>> a string just as long as STRING but beginning with "..." instead of the
>> first three letters of STRING.  What is a valid use case for that?
>
> When STRING is part of a longer string.

I don't see why that is relevant, and one of the few uses of
string-truncate-left in the Emacs sources seems to confirm my doubt,
namely, in gnus-shorten-url, which results in displaying
e.g. "cvs.savannah.gnu.org...emacs.svg?view=log" instead of
"https://cvs.savannah.gnu.org/viewvc/emacs/emacs/etc/images/icons/hicolor/scalable/apps/emacs.svg?view=log".
But if the too-long string is
"https://cvs.savannah.gnu.org/viewv/emacs/emacs/1/", then with the
current string-truncate-left gnus-shorten-url "shortens" it to
"cvs.savannah.gnu.org...ewv/emacs/emacs/1/".  AFAICS replacing the three
characters "/vi" by "..." here just loses information.  Can you show a
specific case where such a length-preserving substitution is preferable?

Steve Berman