[PATCH] fix color.pager = false with "git diff"

[Jeff King <peff@peff.net>]

The color code makes a decision early on about whether to
use colors based on the config and whether we are using a
pager. For the most part, this works, because if we are
using a pager, we will start it more or less immediately.

In the case of diff, however, we delay starting the pager in
case --exit-code is being used. If this happens, then the
color code makes the wrong decision (because it doesn't
yet realize we are using a pager), and we need to correct
the decision after deciding whether to use a pager.

Signed-off-by: Jeff King <peff@peff.net>
---
Original discussion here:

  http://thread.gmane.org/gmane.comp.version-control.git/89599

I have mixed feelings on this one. It's kind of a hack. A more elegant
solution would be totally rewriting the color code to check for the
pager at first output.

In favor of this patch:

  1. It fixes a real bug.

  2. Perfect is the enemy of the good, and I don't care enough about
     this case to refactor the color code.

Against:

  1. It does nothing to fix other times when this ordering problem may
     arise (I don't think there are others, but I didn't check very
     thoroughly. And of course new ones may appear).

  2. The bug was reported over 2 years ago, and hasn't come up since,
     despite remaining unfixed.  Maybe nobody actually cares.

 builtin/diff.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/builtin/diff.c b/builtin/diff.c
index a43d326..cbe15c9 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -318,6 +318,21 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		setup_pager();
 
 	/*
+	 * Special case: we have already examined the config for
+	 * color, but we didn't know at that point whether we were
+	 * going to start a pager. The only case that we care about is
+	 * when we turned on color, but shouldn't have (we will never
+	 * "should have but didn't" because of the pager, since
+	 * a lack of a pager implies either the tty is stdout, in
+	 * which case we do turn on color, or it is not, in which
+	 * case we don't start a pager).
+	 */
+	if (DIFF_OPT_TST(&rev.diffopt, COLOR_DIFF) &&
+	    pager_in_use() &&
+	    !pager_use_color)
+		DIFF_OPT_CLR(&rev.diffopt, COLOR_DIFF);
+
+	/*
 	 * Do we have --cached and not have a pending object, then
 	 * default to HEAD by hand.  Eek.
 	 */
-- 
1.7.3.1.235.gdd6c0