Re: functions can fully unset local vars in other scopes

[Kerin Millar]

Hi Emanuele,

On Fri, 29 Jul 2022 03:59:07 +0200
Emanuele Torre <torreemanuele6@gmail.com> wrote:

> Description:
>   `bash' does not let `unset' fully undeclare local variables. (so that
>   they can be used later as `local' variables without needing to
>   redeclare them I assume.)
> 
>       bash-5.1$ x=abc; declare -p x; unset -v x; declare -p x
>       declare -- x="abc"
>       bash: declare: x: not found
> 
>       bash-5.1$ a () { local x=abc; local -p x; unset -v x; local -p x ;}
>       bash-5.1$ a
>       declare -- x="abc"
>       declare -- x
> 
>   However, other functions are allowed to delete those variables:
> 
>       bash-5.1$ a () { local x=abc; b; local -p x ;}
>       bash-5.1$ b () { unset -v x ;}
>       bash-5.1$ a
>       bash: local: x: not found
> 
>   This enables defininng a "really_unset" function like so:
> 
>       really_unset () { unset "$@" ;}
> 
>   Which may be useful I guess.
> 
>   But I think allowing functions to unset local variables from other
>   functions defeats the whole purpose of having that `unset'
>   behaviour. This enables `local' variable to unexpectedly become global
>   after a function is called.

Though it only goes halfway towards addressing your concerns, 5.0 added a 
localvar_unset option that impedes the behaviour of 'popping' from the 
outermost scope.

$ bash -c 'x=foo; f1() { local x=bar; f2; x=baz; }; f2() { unset x; declare -p 
x; }; f1; declare -p x'
declare -- x="foo"
declare -- x="baz"

$ bash -O localvar_unset -c 'x=foo; f1() { local x=bar; f2; x=baz; }; f2() { 
unset x; declare -p x; }; f1; declare -p x'
declare -- x
declare -- x="foo"

> 
> Fix:
>   I think calling `unset -v x' (where `x' is a local variable not in the
>   current scope) should behave as if it was called in the scope of `x',
>   so `x' should remain declared in that scope with no attributes and no
>   value.
> 
>   It may be nice to also add a "force" option for `unset' that makes it
>   actually unset the variable if it is `local'. Since this could be
>   useful in some cases and it won't be possible after the behaviour is
>   changed.
> 

-- 
Kerin Millar