Re: [BUG] 'diff A...B' fails with multiple merge bases

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> I prepared a patch to reject such a request when there are more than one
> merge base (see below---it is against 1.6.4 maintenance track).  While I
> think giving _one_ possible explanation of what you did since you forked
> would be better than rejecting, which I'll try in a separate message, but
> at the same time it may be misleading to give such an output without
> telling the user that we chose one merge base at random to diff against
> it.

And this is the other one (not relative to the previous patch) that shows
diff since one randomly chosen merge base.

 builtin-diff.c |   26 +++++++++++++++++++++-----
 1 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/builtin-diff.c b/builtin-diff.c
index 2e51f40..1f44f5b 100644
--- a/builtin-diff.c
+++ b/builtin-diff.c
@@ -405,12 +405,28 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		result = builtin_diff_index(&rev, argc, argv);
 	else if (ents == 2)
 		result = builtin_diff_tree(&rev, argc, argv, ent);
-	else if ((ents == 3) && (ent[0].item->flags & UNINTERESTING)) {
-		/* diff A...B where there is one sane merge base between
-		 * A and B.  We have ent[0] == merge-base, ent[1] == A,
-		 * and ent[2] == B.  Show diff between the base and B.
+	else if (ent[0].item->flags & UNINTERESTING) {
+		/*
+		 * Perhaps the user gave us A...B, which expands
+		 * to a list of negative merge bases followed by
+		 * A (symmetric-left) and B?  Let's make sure...
 		 */
-		ent[1] = ent[2];
+		for (i = 1; i < ents; i++)
+			if (!(ent[i].item->flags & UNINTERESTING))
+				break;
+		if (ents != i + 2 ||
+		    (ent[i+1].item->flags & UNINTERESTING) ||
+		    (!ent[i].item->flags & SYMMETRIC_LEFT) ||
+		    (ent[i+1].item->flags & SYMMETRIC_LEFT))
+			die("what do you mean by that?");
+		/*
+		 * diff A...B where there is at least one merge base
+		 * between A and B.  We have ent[0] == merge-base,
+		 * ent[ents-2] == A, and ent[ents-1] == B.  Show diff
+		 * between the base and B.  Note that we pick one
+		 * merge base at random if there are more than one.
+		 */
+		ent[1] = ent[ents-1];
 		result = builtin_diff_tree(&rev, argc, argv, ent);
 	}
 	else