Adding options to commands

[Russ Brown]

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Martin Pool wrote:
> On Thu, Jun 5, 2008 at 7:20 AM, Russ Brown <pickscrape at gmail.com> wrote:
>> I was just looking at getting the diffstat pluging to add a --stat
>> option to the diff command, and so needed to know how to add options to
>> an existing command.
>>
>> For an example I was pointed at the xml-output plugin, which adds
>> options to a number of builtin commands.
>>
>> Looking at the code, it seems the additional options are added by
>> subclassing the builtin command handler.
>>
>> This made me wonder what happens if more than one plugin wants to add
>> options to the same builtin command. Does this magically work, or is it
>> a limitation of the plugin system?
> 
> I don't think it will work if they both subclass the builtin command.
> It seems to me they'd be better off asking for the command currently
> registered under that name (through get_cmd_object) and wrapping that.
>  Then they'll wrap each other in whichever order they register.  (Of
> course it's possible you'll have some bad interactions if they want to
> do contradictory things but that's a separate issue...)
> 
> If this works for you maybe you could add a note on the wiki in
> http://bazaar-vcs.org/WritingPlugins
> 

I'm not actually in a situation where I'm finding extensions clashing: I
just thought about it as a potential problem.

I'll have a play and see if I can get it to break, then see if your
method fixes it. I'll update the wiki if it does. :)

- --

Russ.
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