getopts doesn't update OPTIND when called from function

[Martijn Dekker <martijn@xxxxxxxx>]

I'm writing a shell function that extends the functionality of the
'getopts' builtin. For that to work, it is necessary to call the
'getopts' builtin from the shell function.

The POSIX standard specifies that OPTIND and OPTARG are global
variables, even if the positional parameters are local to the
function.[*] This makes it possible to call 'getopts' from a function by
simply passing the global positional parameters along by adding "$@".

My problem is that zsh does not update the global OPTIND variable when
getopts is called from a function, which defeats my function on zsh. (It
does update the global OPTARG variable, though.)

So, this is another bug report.

I made a little test program that demonstrates this; see below the
footnotes. It succeeds on bash, ksh93, pdksh, mksh, and yash, but not
zsh or (d)ash[*2].

Thanks,

- Martijn

[*] The POSIX standard specifies:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/getopts.html
"The shell variable specified by the name operand, OPTIND, and OPTARG
shall affect the current shell execution environment", which implies
that they are global variables.
    Confusingly, that same page also says: "The shell variables OPTIND
and OPTARG shall be local to the caller of getopts and shall not be
exported by default."
    But I believe that "caller" here means the program that calls
getopts, not the function; POSIX does not support function-local
variables. This interpretation is supported by the added phrase "... and
shall not be exported by default" and by the evidence that the majority
of popular shells pass my test script.
    (Of course it should be possible to explicitly make OPTIND and
OPTARG local using the non-standard 'local' or 'typeset' keyword, but I
believe they should be global by default.)

[*2] (d)ash has a hairier bug where, if getopts is called from a
function, it updates the global OPTIND for the first option but not for
subsequent options, so OPTIND gets stuck on 3. I shall be bothering
their developers separately.

#### begin test script ####

#! /bin/sh

expect() {
    if [ "X$2" = "X$3" ]; then
        printf '%s: OK, got "%s"\n' "$1" "$2"
    else
        printf '%s: BUG: expected "%s", got "%s"\n' "$1" "$2" "$3"
        return 1
    fi
}

callgetopts() {
    getopts 'D:ln:vhL' opt "$@"
}

testfn() {
    expect OPTIND 1 "$OPTIND"

    callgetopts "$@"
    expect opt D "$opt"
    expect OPTARG 'test' "$OPTARG"

    callgetopts "$@"
    expect opt h "$opt"
    expect OPTARG '' "$OPTARG"

    callgetopts "$@"
    expect OPTIND 5 "$OPTIND"
    expect opt n "$opt"
    expect OPTARG 1 "$OPTARG"

    callgetopts "$@"
    expect OPTIND 5 "$OPTIND"

    callgetopts "$@"
    expect OPTIND 5 "$OPTIND"
}

testfn -D test -hn 1 test arguments

#### end test script ####

Output on zsh 5.0.7-dev-4:

OPTIND: OK, got "1"
opt: OK, got "D"
OPTARG: OK, got "test"
opt: BUG: expected "h", got "D"
OPTARG: BUG: expected "", got "test"
OPTIND: BUG: expected "5", got "1"
opt: BUG: expected "n", got "D"
OPTARG: BUG: expected "1", got "test"
OPTIND: BUG: expected "5", got "1"
OPTIND: BUG: expected "5", got "1"

Expected output (on bash, *ksh*, yash):

OPTIND: OK, got "1"
opt: OK, got "D"
OPTARG: OK, got "test"
opt: OK, got "h"
OPTARG: OK, got ""
OPTIND: OK, got "5"
opt: OK, got "n"
OPTARG: OK, got "1"
OPTIND: OK, got "5"
OPTIND: OK, got "5"