difftool: fix dir-diff when file does not exist in working tree

Commit 02c5631 (difftool --dir-diff: symlink all files matching the
working tree, 2013-03-14) does not handle the case where a file that is
being compared does not exist in the working tree.  Fix this by checking
for existence explicitly before running git-hash-object.

Reported-by: Kevin Bracey <kevin@bracey.fi>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/git-difftool.perl b/git-difftool.perl
index 67802922cc..8a75205537 100755
--- a/git-difftool.perl
+++ b/git-difftool.perl
@@ -92,6 +92,12 @@ sub use_wt_file
 		return 0;
 	}
 
+	if (! -e "$workdir/$file") {
+		# If the file doesn't exist in the working tree, we cannot
+		# use it.
+		return (0, $null_sha1);
+	}
+
 	my $wt_sha1 = $repo->command_oneline('hash-object', "$workdir/$file");
 	my $use = ($sha1 eq $null_sha1) || ($sha1 eq $wt_sha1);
 	return ($use, $wt_sha1);