From 8538600c6a51f6b02d1db7f7171f05a9651a27e6 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sat, 17 Feb 2018 22:37:47 +0000
Subject: [PATCH] git-debrebase: bomb on totally ambiguous pseudomerges

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 git-debrebase | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/git-debrebase b/git-debrebase
index cc51f775..b69450ba 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -450,15 +450,23 @@ sub classify ($) {
 			   Contributor => $identical[0]);
     }
     if (@p == 2 && @identical == 2) {
-	my @bytime = nsort_by {
-	    my ($ph,$pm) = get_commit $_->{CommitId};
+	my $get_t = sub {
+	    my ($ph,$pm) = get_commit $_[0]{CommitId};
 	    $ph =~ m/^committer .* (\d+) [-+]\d+$/m or die "$_->{CommitId} ?";
 	    $1;
-	} @p;
+	};
+	my @bytime = @p;
+	my $order = $get_t->($bytime[0]) <=> $get_t->($bytime[1]);
+	if ($order > 0) { # newer first
+	} elsif ($order < 0) {
+	    @bytime = reverse @bytime;
+	} else {
+	    return $unknown->('merge of two identical same-age parents');
+	}
 	return $classify->(qw(Pseudomerge),
 			   SubType => qw(Ambiguous),
-			   Overwritten => [ $bytime[0] ],
-			   Contributor => $bytime[1]);
+			   Contributor => $bytime[0],
+			   Overwritten => [ $bytime[1] ]);
     }
     foreach my $p (@p) {
 	my ($p_h, $p_m) = get_commit $p->{CommitId};
-- 
2.30.2