shopt -u compat* (re)sets BASH_COMPAT to 51

[Mihai Moldovan]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: x86_64-pc-linux-gnu-gcc
Compilation CFLAGS: -march=native -mtune=native -Wall -pipe -g3 -ggdb3 -gdwarf-4
                    -O2 -fno-omit-frame-pointer
uname output: Linux apgunner 5.15.11 #1 SMP PREEMPT Thu Dec 23 09:06:30 CET 2021
              x86_64 Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz GenuineIntel
              GNU/Linux
Machine Type: x86_64-pc-linux-gnu

Bash Version: 5.1
Patch Level: 16
Release Status: release

Description:
        The only way to set a compat level of 50 is to use the BASH_COMPAT
        variable. However, unsetting any compatNN shopt value will (re)set
        BASH_COMPAT to 51 (with bash-5.1), which is not something users might
        expect.

        Technically, the result isn't wrong, since, i.e., shopt -u compat43 did
        what it was asked to - not setting the compat value to 43. It's
        counter-intuitive and the old value should be retained, though.

Repeat-By:
        BASH_COMPAT='5.0'
        declare -p 'BASH_COMPAT'
        eval "$(shopt -p)"
        # alternatively, a simple shopt -u compat44 would suffice
        declare -p 'BASH_COMPAT'

OpenPGP_signature
Description: OpenPGP digital signature