mapfile -t doesn't always remove the delimiter

[Greg Wooledge]

The mapfile builtin command doesn't correctly strip delimiters (when
requested with the -t option) in all cases.

unicorn:~$ echo "$BASH_VERSION"
5.1.4(1)-release

unicorn:~$ printf $'a\xffb\xffc\xff' | { mapfile -t -d $'\xff' array; declare 
-p array; }
declare -a array=([0]=$'a\377' [1]=$'b\377' [2]=$'c\377')

I expected the \377 delimiters to be removed by the -t option.

Other delimiters that I tried, which also fail (aren't removed by -t)
are $'\xfe', $'\xf0', $'\x81' and $'\x80'.

Delimiters which work (are removed by -t) include 'q', $'\x01' and $'\x7f'.

At this point, it looks like any byte with the most significant bit set
triggers the error.


Additional info:

unicorn:~$ locale
LANG=en_US.utf8
LANGUAGE=
LC_CTYPE="en_US.utf8"
LC_NUMERIC="en_US.utf8"
LC_TIME=C
LC_COLLATE="en_US.utf8"
LC_MONETARY="en_US.utf8"
LC_MESSAGES="en_US.utf8"
LC_PAPER="en_US.utf8"
LC_NAME="en_US.utf8"
LC_ADDRESS="en_US.utf8"
LC_TELEPHONE="en_US.utf8"
LC_MEASUREMENT="en_US.utf8"
LC_IDENTIFICATION="en_US.utf8"
LC_ALL=
unicorn:~$ uname -a
Linux unicorn 5.10.0-8-amd64 #1 SMP Debian 5.10.46-5 (2021-09-23) x86_64 
GNU/Linux
unicorn:~$ cat /etc/debian_version 
11.0
unicorn:~$ dpkg -l bash | tail -n1
ii  bash           5.1-2+b3     amd64        GNU Bourne Again SHell