[bug?] Invalid file descriptor ignored

[Martijn Dekker <martijn@inlv.org>]

There is some strange and inconsistent behaviour when trying to write to
a non-open file descriptor. I think the following three test cases
should at least return a non-zero status, but only the third one does:

% echo hi 1>&-; echo $?
0
% { echo hi; } 1>&-; echo $?
zsh: write error: bad file descriptor
0
% echo hi 2>&- 1>&2; echo $?
zsh: 2: bad file descriptor
1

Other shells behaviour, FWIW: All other shells return a non-zero status
for all three cases. (d)ash, bash, yash produce an error message for the
first two cases but not the third. ksh88, ksh93 and {pd,m}ksh are silent
on all three.

Thanks,

- M.