Re: [PATCH/RFC] Pro-Git thanks, Control-flow bug report

[Jeff King <peff@peff.net>]

On Mon, Jul 25, 2011 at 02:50:38PM +0200, Steffen Daode Nurpmeso wrote:

> So while exploring git(1) i recently tried out colours (it's oh
> so coloured for a two, since 2011 three colors vim(1) user -
> fascinating) and found a control flow bug:
> 
>   ?0%0[steffen@sherwood git.git]$ ./git --version
>   git version 1.7.6.233.gd79bc.dirty
>   ?0%0[steffen@sherwood git.git]$ ./git -c color.ui=auto -c color.pager=false diff 2> AU; cat AU
>   git_config_colorbool(color.ui,auto,-1)
>     [pager_in_use(): spawned:0, GIT_PAGER_IN_USE:0]
>     auto_color:1
>     color acc. 2 getenv(TERM)
>   git_default_config(color.pager,false): 0
> 
> So the pager is spawned after the color config setting has been
> queried (and the latter is never updated).

Hmm. What's old is new again, I guess. I posted a patch to fix this
almost exactly 3 years ago:

  http://article.gmane.org/gmane.comp.version-control.git/90427

The patch is kind of an ugly special-case, and nobody else brought it up
in the past 3 years, so it just got dropped. Maybe it's worth taking it
now.

> I'm not aware of the codebase, and so i can't offer a patch,
> unfortunately.  I tried the following change in color.c first,
> but that's not a solution for the real problem:
> 
>   jauto_color:
> 	if (pager_in_use())
> 		stdout_is_tty = pager_use_color;
> 	else if (stdout_is_tty < 0)
> 		stdout_is_tty = isatty(1);
> 	if (stdout_is_tty) {
> 		...

You can't fix it strictly through color.c. The problem is that diff asks
the color code about using colors, _then_ starts a pager. So the color
code doesn't have enough information at the time it is asked to make the
right decision.

A more elegant solution would be to push the query to color.c to happen
at the time of color use, instead of during the startup sequence.

-Peff