xtrace output sets ERRNO to 9 (EBADF)

[Stephane Chazelas <stephane@chazelas.org>]

$ ./Src/zsh -c 'set -o xtrace; ERRNO=0; :; echo "$ERRNO"'
+zsh:1> ERRNO=0
+zsh:1> :
+zsh:1> echo 9
9

Seems to be caused by a double-close. From strace:

dup(2)                                  = 3
fcntl(3, F_DUPFD, 10)                   = 12
close(3)                                = 0
fcntl(12, F_GETFL)                      = 0x1 (flags O_WRONLY)
newfstatat(12, "", {st_mode=S_IFIFO|0600, st_size=0, ...}, AT_EMPTY_PATH) = 0
brk(0x557861189000)                     = 0x557861189000
write(12, "+zsh:1> :\n", 10+zsh:1> :
)            = 10
close(12)                               = 0
brk(0x557861188000)                     = 0x557861188000
close(12)                               = -1 EBADF (Bad file descriptor)

(on Debian GNU/Linux amd64 with 5.9 or git HEAD).

-- 
Stephane