ATTENTION: This patch depends on the following patches described here
<https://inbox.vuxu.org/zsh-workers/CAGdYchufLwUgpKVU6b5eOiF15p0njFr59H1q9XizypwNjzqKzw@mail.gmail.com/>
:
- patch-01-revert-mistaken-errexit-patches.txt
- patch-03-fix-negation-statement.txt

I have found another issue in execlist, which affects the behavior of
ERR_RETURN in convoluted cases that involve at least two &&/|| commands and
a function call. The following example exhibits the issue.

set -o err_return
> fn() { { false; echo fn1 } && echo fn2 }
> fn; echo done
> fn && echo done


The execution of "fn; echo done" prints "fn1", "fn2", and "done". The
execution of "fn && echo done" should print the same but currently prints
nothing.

The problem is that this test
<https://github.com/zsh-users/zsh/blob/291940bae6cc0471c35c73498e873bc58dae9a95/Src/exec.c#L1429>
in "execlist" is too conservative. Inside "fn", "oldnoerrexit" is equal to
"NOERREXIT_EXIT". Indeed the "&&" in "fn && echo done"  first sets
"noerrexit" to  "NOERREXIT_EXIT | NOERREXIT_RETURN". The call to "fn" then
removes "NOERREXIT_RETURN". Thus, at the beginning of "execlist" in the
call to "fn", "noerrexit" is equal to "NOERREXIT_EXIT" and "oldnoerrexit"
is initialized to the same value. Since "oldnoerrexit" is non-zero, the test
<https://github.com/zsh-users/zsh/blob/291940bae6cc0471c35c73498e873bc58dae9a95/Src/exec.c#L1429>
fails
to readd "NOERREXIT_RETURN" for the evaluation of "{ false; echo fn1 }".
Therefore the evaluation of "false" triggers an early return of "fn" wîth
exit status 1, which in turn triggers an early return of the toplevel and
thus nothing is printed.

The solution is to unconditionally set "noerrexit" to "NOERREXIT_EXIT |
NOERREXIT_RETURN" for any command on the left of "&&" and "||" (and for any
command on the right of "!"). The patch does exactly that (and adds a
regression test).

Philippe