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

From: Felipe Contreras <felipe.contreras@gmail.com>
Date: May 18, 2021, 04:27 UTC
Message-ID: <60a3422b9556c_14d1bc2082f@natae.notmuch>
In-Reply-To: <xmqqim3g4ys5.fsf@gitster.g>

Junio C Hamano wrote:

> Felipe Contreras <felipe.contreras@gmail.com> writes:

Show 14 quoted lines

> > Why not use color.pager?
> 
> I dug a bit to refresh my memory and it turns out that the reason we
> should not do so is because it means something totally different.
> 
> color.[ch] defines want_color() that applications like "diff" and
> "log" can use to see if the application is configured to paint its
> output in colors.
> 
> When that layer says for that particular application it should be
> decided automatically, then we call into color.c::check_auto_color()
> which is the only user of pager_use_color (which is set from the
> color.pager configuration variable).  The purpose of that call is to
> ask if the pager is capable of colors.

That is not true. check_auto_color() returns 1 when the fd is a tty.

For example advice() would indirectly call check_auto_color() and no pager is involved.

Inside the help built-in want_color(GIT_COLOR_UNKNOWN) will always return 1 (unless you do something like `git help git > file`).

pager_use_color is completely ignored in this case.

It's used only when 1) the fd is not a tty, 2) it's stdout, 3) git is using a pager... Only _then_ it checks for pager_use_color (color.pager).

So no; the first purpose of check_auto_color() is to find out if the fd is capable of showing colors, secondary, if we are using a pager, then check the user configuration.

In the case we are using a pager it's not check if the pager is capable of colors, the pager could be capable of colors and yet the user would disable them: it's the check for the user preference.

> 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).

> and the color.ui (and color.<cmd>) is about "does the user
> wants output from <cmd> in color?"

> Tying it directly to "color.pager" is wrong.

Why? color.pager is to enable/disable colored output when a pager is in use.

The fact that it's man executing the pager and not git makes no difference to the user.

Cheers.

-- 
Felipe Contreras