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Date: Mon, 06 Feb 2006 06:34:36 -0700
From: Eric Blake <ebb9 AT byu DOT net>
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Subject: Re: Prompt issue within cygwin
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According to Eric Blake on 1/24/2006 7:12 AM:
> 
> Shoot - the bug is still not fixed upstream; I reproduced it with
> bash-3.1-1, readline-5.1-1, and rxvt-2.7.10-6.  One of these days, I hope
> to be able to sit down and figure out where readline is going wrong (it is
> either a readline bug, or a bug in the terminfo database), but it is
> painful to debug.
> 
> 
>>>There is a prompt bug in bash that causes it to miscount the number of
>>>displayed characters.  One workaround was to append '\[\]' to PS1.  Also,
>>>a good habit to get into is to use single quotes in the shell when some
>>>value contains backslashes.
> 
> 
> Unfortunately, appending \[\] to PS1 no longer works with readline-5.1,
> since upstream "fixed" readline to recognize that an empty non-printing
> sequence has no effect on the location of the last non-printing character.
>  However, I think I might be able to recussitate my readline-5.0 hack that
> forcefully treats a single-line prompt with non-printing characters as
> though it had a \[\] appended (and I hope I can make it work at a lower
> level then where empty \[\] is stripped from PS1).  It may be a while, but
> I plan on providing readline-5.1-2 that works around this nasty prompt bug
> as soon as I can.

Chet Ramey, the upstream readline maintainer, FINALLY admitted that his
routines have display bugs when readline is compiled with multi-byte
support, and when a single-line prompt contains invisible characters.  The
problem stems from the fact that there is no reliable way to determine
which column the cursor is currently in, so readline makes some
assumptions that the prompt always starts in column 0 (which is not always
valid):

http://lists.gnu.org/archive/html/bug-bash/2006-02/msg00018.html

Hopefully Chet holds true to his promise and makes readline 5.2 better at
this (although given the history of his past releases, it will be more
than a year away; and he doesn't post his development version control
system online, so the rest of the world is stuck waiting).

- --
Life is short - so eat dessert first!

Eric Blake             ebb9 AT byu DOT net
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