Re: 5.2.15(1)-release: RETURN trap not executed in cmd subst if last statement of fct is not builtin

[Emanuele Torre]

On Sat, Jul 06, 2024 at 01:41:01PM +0200, Jens Schmidt wrote:
> Today I came across this one:
> 
>   [copy-on-select-2]$ echo $BASH_VERSION
>   5.2.15(1)-release
>   [copy-on-select-2]$ foo() { trap 'echo foo' RETURN; /bin/echo bar; }
>   [copy-on-select-2]$ foo
>   bar
>   foo
>   [copy-on-select-2]$ baz=$( foo )
>   [copy-on-select-2]$ echo "<$baz>"
>   <bar>
> 
> I guess that Bash execve's the "/bin/echo" since it runs in a command
> substitution and the trap does not get executed, hence.
> 
> As a work-around, one can tweak function foo so that the last command
> is not an external one, like this:
> 
>   [copy-on-select-2]$ foo() { trap 'echo foo' RETURN; /bin/echo bar; return 
> $?; }
>   [copy-on-select-2]$ foo
>   bar
>   foo
>   [copy-on-select-2]$ baz=$( foo )
>   [copy-on-select-2]$ echo "<$baz>"
>   <bar
>   foo>
> 
> Would this be a bug?
> 
> Should I report it separately on bug-bash?
> 
> Thanks!
> 

This is also reproducible on 5.2.26 and the devel branch:

    bash-5.3$ foo() { trap 'echo foo' RETURN; /bin/echo bar; }
    bash-5.3$ baz=$( foo )
    bash-5.3$ declare -p baz
    declare -- baz="bar"

bash normally disables the exec optimisation if there are EXIT traps,
but apparently it does not do it if there are RETURN traps in a
function.

CC+=bug-bash@gnu.org since this is a bug report

o/
 emanuele6