RFC: Coloured output in bazaar core

[Martin Pool]

On Sun, Aug 3, 2008 at 2:54 PM, Russ Brown <pickscrape at gmail.com> wrote:
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> I had a discussion with lifeless a few days back about colored output
> functionality in bazaar core.
>
> I have been working on adding colour to the diffstat plugin and wanted
> to make it work in a way that would be consistent with any future core
> support for it.
>
> The conclusion to the discussion was to start with a single
> configuration value in bazaar.conf which would enable or disable colour
> for all supporting commands, defaulting to off:
>
> [colour|color] = <Boolean>

It would be good to also support 'auto', to switch depending on the
terminal capabilities.

> I have just added support to the diffstat plugin to support this config
> entry, though there is a bit more code in there than there would be if
> support was in core (handling both spellings, parsing the boolean etc),
> but it does work.

I'm not so keen on supporting both spellings; it adds more code and
there is some potential for confusion.  (Are you going to allow both
spellings in all places?  Does one override the other?)  At any rate
for the initial merge I would just use the 'color' spelling
everywhere, which is the standard in technical use.

> What would it take to get support for this option added to bzr core?
> - From my limited experience of bzrlib, it looks to me like the following
> would be a good start:
>
>  * A get_colours_on() method (or similarly named) somewhere in
>   bzrlib.config which defaults to False. I'm not entirely sure which
>   class (or classes) this needs adding to.

I would look at making this part of the UIFactory.

> I think that would be all we would need to get started, but here are a
> few ideas of additional things that could be added that would enhance
> the feature further:
>
>  * New global options to bzr --no-colour and --no-color which the user
>   can use to disable colour output temporarily for a single execution
>   without having to mess with the config file

It might be clearer to put them just on the particular commands they
affect?  I suppose many of them could eventually use colored output.

>  * Some library that can be called upon to colour up a chunk of text.

That does seem pretty important :-)

Strictly speaking you probably want to use the terminfo library to get
the escape codes through the terminfo library.  In practice I think
almost every user will on a terminal that understands the standard
escape codes (including xterms and the linux and bsd console) and this
may be an unnecessary delay or complication.  Really you could start
with either one.

This is only for Unix; on Windows there is an api to change the text
color of course but I don't know how you would reach it from Python.
But probably someone else here would.

> Any comments or additional ideas? If someone gives me a hint on where to
> add the required code in bzrlib.config I'll submit a patch myself.

If I was writing this I would start by aiming for immediate
gratification by just adding the --color option to diff and making
that produce colored output, then think about how to permanently
configure it on.  And of course there is the colordiff plugin you can
look at.

-- 
Martin <http://launchpad.net/~mbp/>