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

[Chet Ramey]

On 2/12/22 4:11 AM, Mihai Moldovan wrote:
> 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.

Hmmmm. So what you're proposing is that `shopt -u compat43' if compat43 is
not set should not reset the compatibility level to the current version.
OK.

I think we could do this by interrogating $BASH_COMPAT after unsetting the
appropriate compat_NN option.

Or maybe leaving shell_compatibility_level alone if it's > 44 (the last
compat_NN option) and <= DEFAULT_COMPATIBILITY_LEVEL (the current version)
instead of unconditionally setting it to DEFAULT_COMPATIBILITY_LEVEL. But
then you'd be required to unset BASH_COMPAT to get back to the current
compatibility level, which is supported now but not required.

Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/