[libvirt] [PATCH v2]virsh: track alias option and improve error message when option duplicates its alias

[Chen Hanxiao]

> -----Original Message-----
> From: Eric Blake [mailto:eblake at redhat.com]
> Sent: Wednesday, November 13, 2013 9:14 PM
> To: Chen Hanxiao; libvir-list at redhat.com
> Subject: Re: [libvirt] [PATCH v2]virsh: track alias option and improve error
> message when option duplicates its alias
> 
> In addition to Peter's review, it helps if you make your commit message
> smarter by showing before-and-after scenarios, to make it obvious how
> the error message improved.  My quick testing of the 4 possible 'before'
> scenarios:
> 
> $ args="-c test:///default attach-disk test /dev/null vda"
> $ tools/virsh $args --shareable --shareable
> error: option --mode already seen
> $ tools/virsh $args --shareable --mode=shareable
> error: option --mode already seen
> $ tools/virsh $args --mode=shareable --mode=shareable
> error: option --mode already seen
> $ tools/virsh $args --mode=shareable --shareable
> error: option --mode already seen

Thanks for your advice.

> 
> The existing message of "--mode already seen" is absolutely confusing
> for scenario 1, correct for scenario 3, and sort of confusing for
> scenarios 2 and 4.  Your proposed message of "'--shareable' duplicates
> its alias '--mode'" would be wrong for scenarios 1 and 3, but works for
> scenarios 2 and 4.  Are you improving the message for one scenario at
> the expense of a regression in quality of other scenarios?

I lacked of test cases about two same parameters.

> 
> Furthermore, since aliases are (mostly) undocumented, the ONLY people
> that should be using them are historical scripts that already had a
> working command line, and not new users trying to experiment with the
> various options; and working command lines don't have a problem with
> duplicate options.  I think you're trying to address a non-issue.  Since
> neither the '--help' text nor tab completion should be offering an alias
> as a preferred spelling in the first place, it's unlikely that a human
> user is going to be attempting a collision between its alias and the
> canonical spelling.

Thanks, I see.
If we can get rid of auto completion of alias, I think it will be fine enough.

> 
> I'm inclined to just say leave good enough alone, without trying to make
> any further "improvements", as we have reached the point of diminishing
> returns.
> 
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org