Re: Man pages have colors? A deep dive into groff

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: May 18, 2021, 13:21 UTC
Message-ID: <60a3bf5624cbc_15198720876@natae.notmuch>
In-Reply-To: <YKNptH9DL6pe18Dk@coredump.intra.peff.net>

Jeff King wrote:

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> On Mon, May 17, 2021 at 11:27:23PM -0500, Felipe Contreras wrote:
> 
> > > So in short, the color.pager is about "is the pager capable of
> > > colors?"
> > 
> > That's not the case.
> > 
> > Even the documentation says so:
> > 
> >   color.pager::
> >     A boolean to enable/disable colored output when the pager is in
> >     use (default is true).
> 
> I think that documentation misses the reason you'd want to use it.
> Likewise, the commit message introducing it (aa086eb813d) sucks,

Well, it was 2006. Many of the best practices of today were not followed back then.

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> but the
> motivation (from [0]) was:
> 
>   When I use a pager that escapes the escape character or highlights the
>   content itself the output of git diff without the pager should have
>   colors but not with the pager.  For example using git diff with a
>   pathspec is quite short most of the time.  For git diff I have to
>   enable paging manually and run git diff | $PAGER usually but git log
>   uses the pager automatically and should not use colors with it.

This is aligned with what I said: the uswer wants to disable colors when using a pager.

Yes, in this instance it's because the pager doesn't support colors, but that's not always necessarily so. A person with sight problems may use less (perfectly capable of colors), but yet not want to exercise that capability.

It's still a preference.

> For a more concrete example, my pager _does_ understand colors, and I
> would not want to set pager.color to "false" (because then "git log",
> etc, would not show me any colors). But I don't like the man colors you
> are suggesting.

You can change them in your environment.

> I want to be able to turn them off by setting "color.man" or similar
> to false, not by disabling color for everything that is paged.

Sure, for that particular case it does make sense. I'll add that.

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> So color.pager being true is _necessary_ for showing colors in paged
> outputs, but by itself is not sufficient. We have other per-context
> color options (color.diff, color.branch, and so on).
> 
> And so likewise, we would want to avoid turning on colors if the user
> has set color.pager=false. Usually this is done automatically because
> want_color() checks, which knows if we are using the pager or not. But
> if we are going to call out to "man" which will invoke another pager,
> that caller would have to check pager_use_color themselves (it's yet
> another question of whether "the pager can handle color" applies equally
> to the pager that Git will run versus the one that man will run).

Yes, but we still need to check pager_use_color.

Except... Maybe a user has GIT_PAGER set to a colorless pager, and MANPAGER to something fancier, in which case color.pager should be ignored. But that's probably a corner-case nobody is ever going to hit.

Anyway, I've sent an update version with color.man.

-- 
Felipe Contreras