Re: [RFC PATCH 4/4] color.ui config: add "isatty" setting

From: Jeff King <peff@peff.net>
Date: May 31, 2018, 05:38 UTC
Message-ID: <20180531053810.GD17068@sigill.intra.peff.net>
In-Reply-To: <20180530210641.19771-5-avarab@gmail.com>

On Wed, May 30, 2018 at 09:06:41PM +0000, Ævar Arnfjörð Bjarmason wrote:

Show 10 quoted lines

> A co-worker of mine who was using UNIX systems when dinosaurs roamed
> the earth was lamenting that kids these days were using tools like
> "git" that thought they knew better than isatty(3) when deciding
> whether or not something was a terminal, and the state of the
> documentation fixed earlier in this series certainly didn't help.
> 
> So this setting is a small gift to all the UNIX graybeards out
> there. Now they can set color.ui=isatty and only emit fancy colors in
> situations when the gods of old intended, not whatever heuristic we've
> decided to set "auto" to.

I'm having trouble thinking of a case where anybody would actually care about the distinction between these two.

If you're not using "-p", then colors will kick in if isatty() is true. The whole "also check the pager" thing is only because we may check the color isatty() after starting the pager. If we didn't, then nobody would ever see color. If your pager doesn't understand color, then fine. Tell Git not to send it color with color.pager=false.

If you are using "-p", we might send color to your pager even though you weren't originally going to a terminal. But either your pager can handle colors, in which case this is fine, or it cannot, in which case you would already have needed to set color.pager as above to un-break all of the non-p cases.

Is there some case where a pager can only handle color if _it's_ output is going to a tty, and otherwise not? And you'd want color predicated on whether the original output was a tty or not, even if you said "-p"? That's the only case I can think of where the existing config is not sufficient, but I'm having a hard time envisioning a practical use.

Show 6 quoted lines

> As noted here this is *currently* the same as setting color.ui=auto &
> color.pager=false, but I think it's good to explicitly have this
> setting for any future changes. The reason, as now noted in the
> documentation is that the "auto" setting may become even smarter in
> the future and learn even deeper heuristics for when to turn itself on
> even if isatty(3) were returning true.

Are we actually thinking about teaching it deeper heuristics? I think the fact that it _is_ based on isatty() is meant to be understood by the user, and we wouldn't want to change that. True, there is the pager exception, but the point of that is to maintain the "are we going to a tty" model, even in the face of sticking a pager in the middle.

-Peff