Recommended way for plugin to add an option to an existing command?

[Neil Martinsen-Burrell]

On Sat, Mar 19, 2011 at 11:32, Eric Siegerman <lists08-bzr at davor.org> wrote:
> I'm new to plugins and hooks, so forgive me if I'm stating either
> the obvious or sheer nonsense :-/
>
> On Sat, 2011-03-19 at 12:13 +0100, vila wrote:
>>>>>> Neil Martinsen-Burrell <nmb at wartburg.edu> writes:
>>     > What is the recommended way to add an option to an existing
> command
>>     > from a plugin? [...] I'm not sure what the current state of the
> art is.
>
> No idea about the best way to do it, but there's a Command hook
> "extend_command" that looks to give you *a* way.  It's documented
> as being:
>    Called after creating a command object to allow modifications
>    such as adding or removing options, docs etc. Called with the
>    new bzrlib.commands.Command object.

Thanks for the pointer to that.  I'll see if I can make that work.

>>     > What I would like to do is define a template LogFormatter.
> Ideally, I
>>     > would do "bzr log --log-format=template --template-str='{revno}
>>     > {author}'".
>
> As a usability enhancement, consider a syntax that does away with
> "--template-str" entirely, e.g. something like this (by loose
> analogy with revision-spec syntax):
>    bzr log '--log-format=template:{revno} {author}'
>
> As a bonus, this makes the problem of adding an option go away,
> but that's not the main point: the reason I'm requesting it is
> because I'm lazy and don't want to have to type (and remember the
> names of) two --long-option='s when one will do.

Aha, if I am going to be adding options and overriding behavior, then
I can in fact force this syntax "bzr log --template='{revno}
{author}'".  Thanks for the idea.

>> Well, in this case I would try to *avoid* adding an option to the
>> command but instead make the log formatter get the template from a
>> config option.
>
> Being able to specify a format on the command line would be, to
> my mind, the most useful thing about this plugin!  I often want
> to get info about my branch history in some ad-hoc format -- and
> because it's ad-hoc, storing the details in a config file would
> be both pointless and very inconvenient.

I can certainly see where having a configuration option to specify
arbitrary log formats makes sense, but I had in mind the same thing as
Eric, to allow ad-hoc formats from the command line.  Once #491196 is
addressed, these can be addressed by the same mechanism, but until
then, I think a plugin that adds "bzr log --template=..." is a
reasonable stop-gap.

-Neil