[Bug argparse/28081] New: getopt_long doesn't return error on ambigouos option

[Bug argparse/28081] New: getopt_long doesn't return error on ambigouos option

[mlichvar at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

            Bug ID: 28081
           Summary: getopt_long doesn't return error on ambigouos option
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: argparse
          Assignee: unassigned at sourceware dot org
          Reporter: mlichvar at redhat dot com
  Target Milestone: ---

An option which partially matches multiple getopt long options doesn't produce
an error.

Reproducer:
#include <stdio.h>
#include <getopt.h>

int main(void) {
        const char *argv[] = {"a", "--f", "b", NULL };
        int index, c;

        static struct option long_options[] = {
                {"foobar", required_argument, 0, 0},
                {"foobaz", required_argument, 0, 0},
                {0, 0, 0, 0}
        };

        c = getopt_long(3, (char **)argv, "", long_options, &index);

        printf("c=%d index=%d\n", c, index);
}

Actual result:
c=0 index=0

Expected result:
option '--f' is ambiguous; possibilities: '--foobar' '--foobaz'
c=63 index=0

More information:
It seems this doesn't happen when the two options are different in the
required_argument vs no_argument setting.

Observed on Fedora 34 using glibc-2.33-16.fc34.x86_64.

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[mlichvar at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

Miroslav Lichvar <mlichvar at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|getopt_long doesn't return  |getopt_long doesn't return
                   |error on ambigouos option   |error on ambiguous option
            Version|unspecified                 |2.33
           Severity|normal                      |minor

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |NOTABUG
             Status|NEW                         |RESOLVED

--- Comment #1 from Andreas Schwab <schwab@linux-m68k.org> ---
That's not a bug.  The two options are exactly equivalent, so there is no
ambiguity.

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[mlichvar at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

Miroslav Lichvar <mlichvar at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
         Resolution|NOTABUG                     |---

--- Comment #2 from Miroslav Lichvar <mlichvar at redhat dot com> ---
They are not equivalent. They have a different index, which is how the
application where I came across this issue recognizes them.

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[schwab@linux-m68k.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

Andreas Schwab <schwab@linux-m68k.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |NOTABUG
             Status|REOPENED                    |RESOLVED

--- Comment #3 from Andreas Schwab <schwab@linux-m68k.org> ---
You need to use a different val.

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[mlichvar at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

--- Comment #4 from Miroslav Lichvar <mlichvar at redhat dot com> ---
Ok, if you don't plan to fix this issue, it would be good to have it described
in the getopt_long() man page, or at least fix the example it contains to not
use the same val for different options, so new projects are less likely to fall
into this trap. I'll see if I can submit a patch for the man pages.

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[Bug argparse/28081] getopt_long doesn't return error on ambiguous option

[mlichvar at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28081

--- Comment #5 from Miroslav Lichvar <mlichvar at redhat dot com> ---
FWIW, the getopt code checks also for a different flag, not just val and
has_arg. A minimal workaround, at least when the struct config is not
reallocated, is to point the flag to the val itself, e.g.

opts[i].flag = &opts[i].val;

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