[Bug argparse/28317] New: Argp multiple parsers (child parsers) does not work as expected if any two parsers define options that have a common prefix

[Bug argparse/28317] New: Argp multiple parsers (child parsers) does not work as expected if any two parsers define options that have a common prefix

[jivan.pal at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28317

            Bug ID: 28317
           Summary: Argp multiple parsers (child parsers) does not work as
                    expected if any two parsers define options that have a
                    common prefix
           Product: glibc
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: argparse
          Assignee: unassigned at sourceware dot org
          Reporter: jivan.pal at gmail dot com
  Target Milestone: ---

An Argp parser determines whether the user has passed a particular long option
by matching its *shortest unique prefix*, rather than the *whole string*. IMO,
this is undesirable behaviour in and of itself, but it also leads to a nasty
bug
when using child parsers: My command `drat` that I'm developing cannot have an
option called "block" in the main/parent parser whilst also having an argument
called "block-size" in a child parser, because each parser will match the
shortest prefix (i.e. `--b`, `--bl`, `--blo` etc. all suffice for each parser)
and the child parser gets priority, meaning that when I do

`drat read --container /dev/disk0s2 --block 0x123`,

it performs the equivalent of

`drat read --container /dev/disk0s2 --block-size 0x123`,

which is of course not what I want...

This bug is present because Argp relies on the behaviour of `getopt_long()`,
which is defined as follows (from documentation of `_getopt_internal_r()`,
emphasis mine):

> Long-named options begin with '--' instead of '-'. ***Their names may be
> abbreviated as long as the abbreviation is unique or is an exact match for
> some defined option.***  If they have an argument, it follows the option name
> in the same ARGV-element, separated from the option name by a '=', or else the
> in next ARGV-element. When 'getopt' finds a long-named option, it returns 0 if
> that option's 'flag' field is nonzero, the value of the option's 'val' field
> if the 'flag' field is zero.

The emphasised behaviour is implemented in `process_long_option()`, in the
first
`if (pfound == NULL)` block, which can be found in glibc git commit `2738480a`
(latest commit on `master` at time of writing), file `posix/getopt.c`, lines
221-307.

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[Bug argparse/28317] Argp multiple parsers (child parsers) does not work as expected if any two parsers define options that have a common prefix

[jivan.pal at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28317

Jivan Pal <jivan.pal at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |WORKSFORME

--- Comment #1 from Jivan Pal <jivan.pal at gmail dot com> ---
Turns out there was a bug in my code, and Argp handles this situation properly
to avoid such conflicts.

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